~sRadiance Digest, v2n2
Dear Radiance Users,

Here is the latest backlogged collection of electronic mail exchanges on
various topics of hopeful interest.  As always, you can search for the
subjects you want.

	STRANGE_VIEWS		Methods for generating odd images
	SMLFLT_OPTION		Problems with SMLFLT compile switch in 2.0
	ANTIMATTER		How to use antimatter type
	DAYLIGHT_SIMULATION	Understanding daylight simulation options
	LUMINOUS_EFFICACY	Change in luminous efficacy between 1.4 and 2.0
	RPICT_PARAMETERS	What are the useful ranges of rpict parameters?
	GENSURF			New gensurf capabilities and making teapots
	ALIASING		Aliasing and image representation
	SHARED_PICTURES		Sharing picture files
	AMIGA_PORT		New port available for Amiga
	DECSTATION		Problems running on DECstations
	INFRARED		Using Radiance in infrared spectrum
	SPECULARITY_BUG		Bug in specular highlights of 2.0
	VIEW_INFO		Getting view information from files
	BACKGROUND_COLOR	Changing the background color
	UPFRONT_TRANSLATOR	Translator now available for Alias UpFront!
	SCENE_FLATTENING	Flatting Radiance scene descriptions

I intend to release version 2.1 shortly, and will make an announcement
at the appropriate time.

-Greg

==========================================================================
STRANGE_VIEWS

Date: Wed, 15 Jan 92 16:25:30 -0500
From: David Jones  <djones@lightning.McRCIM.McGill.EDU>
To: Greg Ward <greg@hobbes.lbl.gov>
Subject: Radiance question

Hi Greg,

I would like to generate an image which, instead of pixels indexed
by X and Y on an image PLANE, would have pixels indexed by angles
of azimuth and elevation.  I know I could work out some
transformation to take a rendered image and "warp" it, but it would be
much more efficient to do it directly.

Any suggestions?

thanks,
  Dave

Date: Wed, 15 Jan 92 16:06:30 PST
From: greg (Gregory J. Ward)
To: djones@lightning.McRCIM.McGill.EDU
Subject: Re:  Radiance question

Hi Dave,

Nice to hear from you again.  How have you been getting on in your new
position?

I assume by your question that the -vta fisheye view type is not satisfactory
for your purposes.  This option does produce an image with similar properties
to those you are asking for, but the center of the image corresponds to a
polar angle of 0 and surrounding pixels correspond to a polar angle that is
proportional to the distance from the image center.  Azimuth angle can be
measured as distance (in radians) about a circle whose center is the center
of the image.  I can give you the equations for theta and phi as a function
of pixel location for this type of image if you like.

To produce an image whose upper left corner is (theta,phi)=(0,0) (theta is
the polar angle and phi is the azimuth), and whose upper right corner is
(theta,phi) = (0,2pi), and whose lower left corner is (pi/2,0), use the
following command (setting the -e values to suit):

	% cnt 256 512 | rcalc -e 'xres:512;yres:256' \
		-e 'vpx:0;vpy:0;vpz:0' \
		-e 'vdx:1;vdy:0;vdz:0' \
		-e 'vux:0;vuy:0;vuz:1' -f polar.cal \
		| rtrace [options] -faf octree \
		| pvalue -r -df -y 256 +x 512 > polar.pic

Here is the file polar.cal:

{
	Compute polar directions for a given
	view point, direction and up vector
}
	{ compute right and top vectors }
rux : vdy*vuz - vdz*vuy;
ruy : vdz*vux - vdx*vuz;
ruz : vdx*vuy - vdy*vux;
lru : sqrt(rux*rux+ruy*ruy+ruz*ruz);
rx : rux/lru; ry : ruy/lru; rz : ruz/lru;
lvd : sqrt(vdx*vdx+vdy*vdy+vdz*vdz);
dx : vdx/lvd; dy : vdy/lvd; dz : vdz/lvd;
tx : ry*dz - rz*dy;
ty : rz*dx - rx*dz;
tz : rx*dy - ry*dx;

	{ get input pixel values }
x = $2; y = $1;

	{ comute theta, phi directions }
theta = PI/2 * (y+.5)/yres;
phi = 2*PI * (x+.5)/xres;
ct = cos(theta); st = sin(theta);
cp = cos(phi); sp = sin(phi);

	{ output view point }
$1 = vpx; $2 = vpy; $3 = vpz;

	{ output view direction }
$4 = dx*ct + rx*cp*st + tx*sp*st;
$5 = dy*ct + ry*cp*st + ty*sp*st;
$6 = dz*ct + rz*cp*st + tz*sp*st;

----------------------------------
I gave the above a try and it seems to work for my simple example.  I hope
that changes of view and output resolution are clear, and I think
you can figure out how to modify it for different ranges of theta and phi.

If you don't have version 2.0 of Radiance, this is not going to work
without some modifications.  Let me know how it turns out!

-Greg

===================================================================
SMLFLT_OPTION

Date: Thu, 16 Jan 92 18:22:19 -0500
From: David Jones  <djones@lightning.McRCIM.McGill.EDU>
To: Greg Ward <greg@hobbes.lbl.gov>
Subject: trouble with lighting

I know I've enountered this problem before, but I forget the solution.
Some of my surfaces look speckled.  I have deposited a file
in hobbes:/pub/xfer/speckle.pic.Z.
I dumped this out of rview.  Do you have any sugestions?

dj

Date: Thu, 16 Jan 92 15:47:17 PST
From: greg (Gregory J. Ward)
To: djones@lightning.McRCIM.McGill.EDU
Subject: Re:  trouble with lighting

Hi David,

Actually, I don't think you've run into this exact problem before.  There
are other instances where using the -dj option can cause black spots, but
I don't think that's the case here.  The problem (my guess) is that you
said you wanted to use huge models during the Q&A session before building
the 2.0 distribution.  Answering yes to this particular question can (as
you were warned) result in some artifacts.  This is the price of using
single rather than double precision numbers for the geometry calculations.
I don't recommend it unless memory is really at a premium, for obvious
reasons.

To rebuild the distribution using double precision arithmatic throughout,
do a makeall clean followed by a makeall install.  Say "yes" to the question
about modifying the rmake command, and remove the -DSMLFLT option therein.

If -DSMLFLT is not in your rmake file, then I'm wrong and I'll have to
think a little harder to figure out what's going on.

-Greg

Date: Thu, 16 Jan 92 19:43:56 -0500
From: David Jones  <djones@lightning.McRCIM.McGill.EDU>
To: greg@hobbes.lbl.gov
Subject: Re:  trouble with lighting

and have you done away with "x11dev" ?
I can't tell whether I botched the install or
whether an script I use explicitly refers to x11dev when it is no
longer needed.  I the old x11dev from before and it seems to work.
I seem to have trouble changing the viewpoint.  For example,
I would change it to 100 100 50 and then it would
be 3.399, 3.399, 1.777 (or something else way off).  If this persists
after the SMLFLT change, I'll let you know.  Otherwise don't worry about it
unless it sounds familiar.

dj

Date: Fri, 17 Jan 92 09:33:21 PST
From: greg (Gregory J. Ward)
To: djones@lightning.McRCIM.McGill.EDU
Subject: Re:  trouble with lighting

Hi Dave,

Thanks for pointing out the problem with viewpoint changes.  It's a bug
associated with the SMLFLT option that I hadn't caught.  It will be fixed
in the next distribution.  I don't think enough people are using this
compile switch to make it worth sending out a patch.

The X11 driver is now built in as the default in rview, so you can either
specify no -o option or use -o x11 if you want to be explicit.  The old
x11dev separate program driver will still work, but it's less efficient.

-Greg

============================================================
ANTIMATTER

Date: Fri, 17 Jan 92 13:34:09 -0500
From: David Jones  <djones@lightning.McRCIM.McGill.EDU>
To: greg@hobbes.lbl.gov
Subject: Re:  I may be right ...

Sorry for all the questions today, but ...

I want to construct a shape and I think antimatter is appropriate, though
I have never been able to get antimatter to work.  I don't think I
understand the instructions in ray.1

I want to start with a cylinder CYL1 made of material MAT1
and then take another cylinder CYL2 which intersects CYL1 and cut out
the intersection.  I don't want CYL2 visible, but when a ray passes
from the invisible CYL2 into the volume of CYL1 I want a surface to 
be visible and made of MAT2.

Can I do this with antimatter?

dj

Date: Fri, 17 Jan 92 13:54:48 -0500
From: David Jones  <djones@lightning.McRCIM.McGill.EDU>
To: Greg Ward <greg@hobbes.lbl.gov>
Subject: last one for today I hope

Greg,

So now I have a complicated scene with lots of Radiance description files.
I get the following error message:

oconv room2.r > room2.oct
xform: (standard input): unknown object type "xform"
xform: (standard input): unknown object type "xform"


I know this will be easy to fix but where the heck in all the files
oconv has looked does this error occur?  Would it be easy
to add a "-v" option to "oconv" that printed all the file names
as things were opened and closed?  This will pinpoint where this
xform error message is coming from.

dj

Date: Fri, 17 Jan 92 11:18:32 PST
From: greg (Gregory J. Ward)
To: djones@lightning.McRCIM.McGill.EDU
Subject: Re:  I may be right ...

MAT1 cylinder CYL1
0 0 7 ...

void antimatter AMAT2
1 MAT2
0 0

AMAT2 cylinder CYL2
0 0 7 ...

AMAT2 ring CYL2.cap1
0 0 8 ...

AMAT2 ring CYL2.cap2
0 0 8 ...

The above should work as you describe.  The rings at each end are necessary
to make CYL2 an enclosed solid.  Remember that the materials MAT1 and MAT2
cannot be of type trans or glass, and that the viewpoint must be outside of
all volumes involved.

The second problem is more difficult.  I suppose a verbose option could
be added that would mention every opening of a file or starting of a
command in oconv and xform, but the output would be voluminous to say the
least.  I recommend instead that you use the following command to try to
localize the error:

	% xform -e room2.r |& more

The error message will appear shortly before the correspoding point in
the expanded file.

-Greg

Date: Sun, 19 Jan 92 16:26:00 -0500
From: David Jones  <djones@Olympus.McRCIM.McGill.EDU>
To: Greg Ward <greg@hobbes.lbl.gov>
Subject: "popen" woes

So I can't tell whether this is the fault of my radiance description
files (though I really doubt it) or a bug in Radiance or
some problem with our SPARCs.

I am still getting difficulties with "oconv file.r" when "file.r"
contains a lot of recursive "! cat otherfile.r | xform ...".

The new twist is that I am printing out debugging messages
to trace your popen() and pclose() calls.

The symptom is that "oconv" just hangs midway through its job, but
only sometimes.  If I kill the process, delete the ".oct" file and
restart it, then it might work the next time.

How would oconv react if the system ran out of process-table entries
or max # of open files, or something like that.  Would it silently hang?

dj

Date: Sun, 19 Jan 92 15:33:35 PST
From: greg (Gregory J. Ward)
To: djones@Olympus.McRCIM.McGill.EDU
Subject: Re:  "popen" woes

Hi Dave,

You shouldn't even be using "cat file | xform [args]" -- "xform [args] file"
is much more efficient and involves fewer processes.  You should also include
"-e" as the first optiont to xform to reduce the number of open processes.
I don't know what happens when the system runs out of process table entries
under SunOS.  If you run out of open file entries (although a depth up to
32 is safe on most machines), then oconv will report an error message.

The most common reason for oconv to hang is if you forgot to give xform or
some other command an input file and it is trying therefore to read from the
standard input.  This has unpredictable results, which is consistent with the
behavior you are reporting.  Look out for commands such as "cat | xform .."
or "xform [args]" without a file name.

I hope this helps.
-Greg

=================================================================
DAYLIGHT_SIMULATION


Date: Fri, 17 Jan 92 09:42:41 PST
From: kovach@ise.fhg.de
Subject: Radiance
To: GJward@lbl.gov

Hi Greg, 

I just left LBL and already I have more questions.  I just
talked to Peter Ap. about radiance and I have a few questions about
it.  I think it would be a great tool to use to get an idea on
the irradiation distribution on a outer building surface and where
the best place would be for PV modules.  

I have two questions to that point:

1. I need the values of incident irradiation and are these available
as an output of the program?  (Or could an extension to the program
be written to obtain a output data file (for example) with the incident
irradiations in it??)  How much work would it entail?  Would the 
person have to be very familiar with the code of the entire program
or just a part of it?

2. How long would it take to simulate the exterior of a building
with a few overhangs, neighboring buildings , ambient conditions
(eg. reflection from white surfaces) and with a resolution of
6 " in real space??  How about the same conditions with a 
resolution of 12 " in real space?

A rough estimate to these questions would be helpful!  (P.S. Peter
Jaegle and I tried the 'talk' command but were unable to make
a connection!)

Thanks ,   Anne Kovach

From: greg (Gregory J. Ward)
To: kovach@ise.fhg.de
Subject: Re:  Radiance

Hi Anne,

I think that it wouldn't be too difficult to use Radiance for the purpose
you describe.  With version 2.0, it is possible to get either individual
irradiance values or irradiance pictures using rtrace and rpict, respectively.
It is not necessary to do any programming.  I will be happy to help you with
the right commands at the appropriate time.

In reference to your second question, the time required for geometric
modeling depends on whether or not you use a CAD program to do it and
how familiar you are with this type of work.  Assuming that you are just
a beginner and have no CAD program or modeling experience (but keeping
in mind that you are a bright woman), I would guess that it will take
you between a few days and a week to get the exterior model shaped up
using a text editor and working directly with Radiance.  I don't think
the resolution will make that much difference in the modeling time.

-Greg

From: sick@ise.fhg.de
Subject: falsecolor units
To: greg@hobbes.lbl.gov (gregory ward)
Date: Tue, 21 Jan 92 11:03:43 MEZ

Hello,

I started working with Radiance a few weeks ago. Peter Apian-Bennewitz
was a great help in getting started.

I used the new falsecolor program which might be very helpful for me since
I often need quantities (numbers) rather than qualities (nice realistic
pictures). Now here is my problem:

I do not know the "old luminance unit" (dictionary) nit. How does it
convert to lm/m*m-sr ?  I am also confused with the options "s" and
"m": Is the value of s a multiplier of 1000 or replaces it 1000?
Should it be set to the highest expected value of , well, luminance,
illuminance radiance or irradiance?  If I change the multiplier for a
unit conversion, I assume that s is not affected. Correct?  Finally, to
make me get both a quick correct result and an example to follow the
conversions, could you tell me how to produce a falsecolor picture with
values of irradiance in W/m*m?

I really appreciate your efforts. The work I am currently doing will be part
of a presentation at an IEA SHCP Task 16 meeting in Madrid at the beginning
of February. Depending on the outcome of the discussion, Radiance might become
a major tool for the group. So much as an incentive for you ...

Sincerely,

		Fred Sick

Date: Tue, 21 Jan 92 08:51:46 PST
From: greg (Gregory J. Ward)
To: sick@ise.fhg.de
Subject: Re:  falsecolor units

Hello Friedrich,

The "scale" value of falsecolor as set by the -s option determines only the
maximum charted value in the image.  This is as you supposed unaffected by
the -m "multiplier" option which determines the units being charted.

The luminance unit of 1 nit is in fact 1 lumen/steradian/m^2, so it is already
in SI units.  A multiplier of -m 1 produces values in the native unit of
Radiance, which is watts/steradian/m^2.

The only way to correctly produce illuminance or irradiance values is by
rendering the image with the -i option of rpict.  Then, simply apply
falsecolor as you would have to produce luminance or radiance values.

If any of this is still not clear to you, please do not hesitate to ask
me further questions.

-Greg

Date: Mon, 27 Jan 1992 18:38:06 EST
From: MICHAEL DONN <donnmr@matai.vuw.ac.nz>
To: greg@hobbes.lbl.gov
Subject: Daylighting models in RADIANCE 2.0

We are trying to model the "real" sky using radiance and wish to test a
couple of simple buildings against our artificial sky (a mirror box) which
we have evaluated against real measurements in a real building we analysed
for the architects last year. Our difficulty is knowing exactly what gensky is
modelling. As we are using an artificial sky, there are all the usual problems
of defining what is typical overcast cloudy sky luminance, and what its
distribution is. 

Some of our problem is in knowing exactly what the -av parameter does in Rpict;
it is also in knowing what parameters to input to skyfunc in order to 
properly model the sky clearness etc; and, it is also to model the sun's
luminance allowing for local conditions as precisely as we can.

In summary, in order to calibrate RADIANCE, we are modelling a simple grey box
with one window, and comparing the daylight factors, and the actual light
levels predicted against each other, and need to know as much about the 
assumptions behind the RADIANCE values as we do about the other mirror box 
values.

From greg Mon Jan 27 09:02:00 1992
Return-Path: <greg>
Date: Mon, 27 Jan 92 09:01:53 PST
From: greg (Gregory J. Ward)
To: donnmr@matai.vuw.ac.nz
Subject: Re:  Daylighting models in RADIANCE 2.0
Status: RO

The gensky program in Radiance uses the standard CIE distributions for
clear and overcast skies.  The precise formulas used are in the source
file ray/src/gen/gensky.c and ray/src/gen/sun.c and the function file
ray/lib/skybright.cal.  This function file is where the actual distribution
is calculated, using the zenith luminance and ground luminance values
plus the sun direction given by gensky.

Zenith brightness is calculated from the solar altitude and atmospheric
turbidity using a formula developed from data gathered in San Francisco,
which may not be very accurate for other places on the globe.  For better
control, it is preferable to measure or assume a certain zenith brightness
and give it directly to gensky using the -b option.

It is not too difficult to develop your own function file to specify
whatever sky distribution you like.  Gensky is provided only as a basic
skylight approximation.

-Greg

Date: Mon, 16 Mar 92 18:46:08 PST
From: greg (Gregory J. Ward)
To: edu@leicester-poly.ac.uk
Subject: Re:  daylighting

Hi John,

Thanks for your recent letter.  I will attempt to answer your questions:

> a)  Having used mkillum for the windows, will one or more ambient bounces for
> the interior space only re-distribute light in the space (necessary if
> light-shelves etc. are present) or will the mkiwindow description allow more
> light from the outside to enter the space messing up the calculation?
> Perhaps a note could be added to the Tutorial about this.

The illum created by mkillum will block all "ambient" rays during the
calculation, maintaining the correct energy balance.  You can set the
-ab parameter to whatever value you like, as it will only be used to
compute interreflection within the space.  (That is, assuming you don't
have any cracks or other places where light might leak through.)  I will
try and add an appropriate note to the tutorial, as you suggest.

> b)  I would appreciate some guidance about appropriate values of av to use in a
> simulation and how they are determined.

I wish I had a definitive answer to this question.  Unfortunately, there is
no general way to set the ambient value that works for every scene.  My best
recommendation is to use rview in the following manner.  Start the program
with the -ab parameter set to 1.  Run it for a short while at an appropriate
viewpoint, then set ab to zero using the command "set ab 0".  Immediately
afterwards, try setting the av parameter to different values until the
new pixels being computed seem to match fairly well to the original ones
computed when the interreflection calculation was on.  (If you're clever,
you can figure out a ballpark starting value but I think I'd have to 
show you how.)  I suggest that you set a grey ambient value for the most
natural color rendering (eg. av .5 .5 .5).

Alternatively, it is possible to compute an approximate value for the
-av parameter based on room reflectances and light source intensities,
but this does not work very well in daylight situations.

> c)  The dayfact script.  I have been looking at ways of speeding this up, using
> a coarser grid and larger radius for filtering is a possibility (I suspect i'm
> not using the most efficient a* settings either).  On the practical side I
> have modified it produce 10 contour levels up to a maximum of DF = 10, 20 or
> 40, depending on the users expectation.  Also, it's worth keeping the pic file
> in the event of a poorly chosen range of levels.  Since, i'd prefer lines,
> and since these appear mid-way between markers, i'll try to find a way to set
> the marker to match the contour level directly above.   Do you want me to send
> you the end product?  Also, the conversion factor to Lux is 470, should it
> be 179?

Didn't I send you my repaired version of dayfact?  I thought I had fixed the
incorrect value of 470 and also made it keep the pic files around.  I can
send the latest for you to work on if you like.  I would like to see your
finished product, but it would be better if you started with the most current
version!

> d)  Am I right in thinking that I can use the indirect calculation as long as
> I don't have any reflecting surfaces exterior to the building?  Or do I just
> have to get rid of the ground plane.

You should always be able to use the indirect calculation, it just so happens
that it doesn't work very well when you have a large ground plane due to the
adaptive sampling algorithm used in 2.0.  (Thank you, by the way, for showing
me just how bad it can be!)  You are better off getting rid of the groundplane
and just using a light source or illum for the window with the skyfunc
distribution, which already accounts for reflection from a groundplane.
If you have external reflecting surfaces, then you must either use mkillum
(recommended) or an interreflection calculation.  If you use an interreflection
calculation with 2.0, then you had better make the ground plane small or get
rid of it altogether.  If you want to have other external surfaces, that
should still work.  (I apologize for this rather convoluted answer.
I hope you managed to untangle my meaning.)

-Greg

From: Environmental Design Unit <edu@leicester-poly.ac.uk>
Date: Mon, 30 Mar 92 14:03:03 BST
To: greg@hobbes.lbl.gov
Subject: Daylighting Calculations

Hello Greg,

A hue-sat color wheel would be nice addition, especially for colour matching
paint samples.  In the meantime, a cut-down list of colours from rgb.txt
does fine.

Just for a change, i'd like to ask you some questions about daylighting
calculations.


a)  Sky models and conversions factors.

The zenith radiance is evaluated in "gensky.c" as 

              if (cloudy) {
                      zenithbr = 8.6*sundir[2] + .123;
                      zenithbr *= 1000.0/SKYEFFICACY;
              } else {

and ground radiance as

      if (cloudy) {
              groundbr = zenithbr*0.777778;
              printf("# Ground ambient level: %f\n", groundbr);
      } else {


and horizontal illuminance in lux is simply

ground ambient level * PI * luminous efficacy.

O.K. so far, but the luminous efficacy definitions in "color.h"
have me confused -

				/* luminous efficacies over visible spectrum */
#define  MAXEFFICACY		683.		/* defined maximum at 550 nm */
#define  WHTEFFICACY		179.		/* uniform white light */
#define  D65EFFICACY		203.		/* standard illuminant D65 */
#define  INCEFFICACY		160.		/* illuminant A (incand.) */
#define  SUNEFFICACY		208.		/* illuminant B (solar dir.) */
#define  SKYEFFICACY		D65EFFICACY	/* skylight */
#define  DAYEFFICACY		D65EFFICACY	/* combined sky and solar */

It looks as if the zenithbr for a cloudy sky is defined in terms of
lum eff = 203 lum/W, whilst the multiplier in "dayfact" is 179 lum/W.
Am I missing the point somewhere?  I have tried, without much success, to
locate papers/texts on sky models and luminous efficacy values for my own
notes.  I would appreciate some recommendations if you have them to hand.

b)  Dayfact output.

The "dayfact" pictures showing daylight factors and lux levels for our
new engineering building (floor plan 25m by 7m, 56 windows and light
shelves) was not terribly satisfactory - bands (and lines) were broken
and it was difficult to determine the areas they enclosed.  However,
gaussian filtering of the saved illuminance picture improved matters
greatly.  Single pass filtering with r=3 proved enough for bands - pictures
with lines were even better.  Do you want me to mail you results as a
uuencoded tar.Z file? [size < 1Mb]

I wanted to compare the effects of filtering at different radii in one
picture by using "pcompos" to put four illuminance pictures in columns to
make one illuminance picture file for "dayfact".  This strategy would be
useful for comparing the consequences of the different a options
for "rtrace".  To my surprise, "dayfact" determined lux values for the
combined pictures approx 1/4 what they were for individual pics!  So,
stroke monolith, toss bone in air... four pics, 1/4 the lux values, something
to do with the area or num of pics?  Looked closely at "falsecolor"
and "dayfact" scripts, but couldn't find where picture area was significant.

c)  Changes to dayfact.

For my own use i've set ten bands/lines for df and lux
pics and default maximum values for both.  Lines do show up better than bands,
especially after r=3 filtering, but the problem remains about the values appearing
midway.  Could you suggest a fix for this.  For a linear scale, adding the smallest
value to each of the values in the list would cure it, as long as we remember
that the number refers to the line above.  The scales would come out better also e.g
0.5, 1.0, 1.5... instead of 0.25, 0.75, 1.25... ( for -s 10 -n 10 ).  I would
like to use "dayfact" on multiple illuminance pictures of the same scene, if you
confirm that it simply scales with the number of pics in the composite I will
add a multiplier option also.  Not forgetting, large radius filtering to smooth
the illuminance picture.

I think this is everything .... for the moment.

As always, thanks for the continued support.

-John Mardaljevic    edu@leicp.ac.uk

Date: Mon, 6 Apr 92 17:55:27 PDT
From: greg (Gregory J. Ward)
To: edu@leicester-poly.ac.uk
Subject: Re:  Daylighting Calculations

Hello John,

Sorry for the delay in my response.  I was away at a meeting.

a) Sky models and conversion factors

The efficacy values listed in color.h are over the visible spectrum only,
so may disagree with some other values you have seen.  You are correct
in pointing out the discrepancy between the value used in gensky.c vs.
the value used in the dayfact script.  To reproduce the original photmetric
values, these two factors should be identical if a grey sky were used.  Since
the sky is not white, we should be using a different value to account for
the relative efficiency of the sky's spectrum, coupled with an appropriate
RGB multiplier on the source in the scene file.  Unfortunately, I did not
have a good spectral curve for the sky, so I used the CIE standard for the
combined sun and sky, D65.  Now that you raised the topic for reexamination,
though, I see that the choice of D65EFFICACY was not a good one because
the efficacy of the sky should be lower than white light due to its
bluish tint, not higher.

The correct sky efficacy should be something like 162, which when combined
with an RGB color of .8 .9 1.3 would yeild approximately the correct result.
Since I don't know what it really should be, you can adjust your RGB color
to 1 1.126 1.626 and you should get the right luminances, anyway.

I should change this stuff.  I only wish I had some decent references myself.

b) Dayfact output

I do not know where the factor of 1/4 could be coming from.  Please send
me a more detailed description of this problem, using "getinfo" to send
me the headers of the resulting renegade pictures.

c) Changes to dayfact

I have modified the script px/falsecolor.csh to put the contour lines
on the values rather than between.  I should have done it this way to
begin with.  You only need to change the following line from:

	boundary(a,b) : neq(floor(ndivs*a),floor(ndivs*b));

to:

	boundary(a,b) : neq(floor(ndivs*a+.5),floor(ndivs*b+.5));

Then copy the file to falsecolor in your executable directory.

-Greg

=================================================================
LUMINOUS_EFFICACY

Date: Wed, 29 Jan 92 07:42:35 EST
From: spencer@cgrg.ohio-state.edu (Stephen N. Spencer)
To: gjward@lbl.gov
Subject: Differences in Radiance v2.0?

Greg, we've been testing Radiance v2.0 (the scanline-fixed version) and have
come up with some differences in how images look.  In specific, light sources
seem to be brighter in version 2.0 than in version 1.4.

I can upload a pair of images, both calculated with the same script, one under
1.4 and one under 2.0, if you'd like to look at them, to get a better idea of
what I mean.  

I honestly don't know if it is an enhancement (read: the 1.4 method wasn't 
correct) or if it is a bug (read: the 2.0 method isn't correct) so I'd like to
understand why these images are different.

Stephen N. Spencer  		     |                      Ride Bike!  ,__o
ACCAD - The Ohio State University    |                                _-\_<,
1224 Kinnear Road Columbus OH 43212  | Indigo Girls Mailing List:    (*)/'(*)
spencer@cgrg.ohio-state.edu	     | indigo-girls-request@cgrg.ohio-state.edu
       "Usenet is like Tetris for people who still remember how to read."

Date: Wed, 29 Jan 92 09:11:40 PST
From: greg (Gregory J. Ward)
To: spencer@cgrg.ohio-state.edu
Subject: Re:  Differences in Radiance v2.0?

Hi Steve,

Before you upload your images and scripts, let me suggest a possible cause
and you can decide if this is what's happening.

Between version 1.4 and 2.0, I corrected the value for the luminous efficacy
of white light from 470 lumens/watt down to 179 lumens/watt.  This value
is used at two points in a normal calculation.  First, to convert light
fixture lumens to watts in ies2rad or a manual conversion process.  Second,
to convert watts back to lumens in ximage or similar programs that display
luminance values.  Since the conversion value is used in a reciprical
fashion in these two steps, the overall effect is null as long as the
same value is used each time.

However, if you are judging by picture "brightness", ie. exposure value
and screen brightness, using the same initial IES file as version 1.4 of
Radiance, you will see a difference because version 2.0 uses a smaller
value for luminous efficacy and thus produces brighter images.  The new
version is more correct.

You can read about this change a bit more in the ReleaseNotes file in the
ray/doc/notes subdirectory of the distribution.

-Greg

===================================================================
RPICT_PARAMETERS

Date: Thu, 30 Jan 92 11:41:57 PST
From: greg (Gregory J. Ward)
FAXnumber: 01149866933541
FAXfrom: "Greg Ward, Lighting Research, LBL, (510) 486-4757, fax 4089"
FAXto: "Martin Mock, ABT ASIV43/LIZ"

Hi Martin,

Here goes with my best shot at explaining the rpict parameters.  The
"min" value gives the fastest, crudest rendering.  It is not
necessarily the smallest value numerically.  The "fast" value gives
a reasonably fast rendering.  The "accur" value gives a reasonably
accurate rendering.  The "max" value gives the ultimate in accuracy.

Param	Description		Min	Fast	Accur	Max	Notes
=====	====================	=====	=====	=====	=====	=====
-sp	pixel sampling rate	16	8	4	1
-st	sampling threshold	1	.15	.05	0
-sj	anti-aliasing jitter	0	.6	.9	1	A
-dj	source jitter		0	0	.7	1	B
-ds	source substructuring	0	.5	.15	.02
-dt	direct thresholding	1	.5	.05	0
-dc	direct certainty	0	.25	.5	1

NOTES:
	A) This option does not affect the rendering time
	B) This option adversely affects image sampling (ie. use -sp 1)

In the next version of Radiance (2.1), the options -sp, -sj and -st will
be renamed -ps, -pj and -pt, respectively.  This is to avoid conflict
with some new options that will be added for sampling semi-specular
reflections.

In general, jittering is a way to reduce image artifacts by
introducing Monte Carlo sampling into the rendering process.  This
technique was introduced by Rob Cook in his landmark paper on
"Distributed Ray Tracing" in the 1984 Siggraph proceedings.

If you want more information on the sampling techniques used in the
direct lighting calculation, you should read the paper I wrote for
the 1991 Eurographics Rendering Workshop.  I have sent you a copy.

Hope this helps explain things a little.
-Greg

========================================================================
GENSURF

To: greg@hobbes.lbl.gov
Date: Fri, 31 Jan 92 8:38:23 CST
From: scoggins@mc1.wes.army.mil

Hi Greg:

I would be interested in trying out you new gensurf.  Jerry Ballard and
I are working on rendering outside scenes using measured terrain elevation
data.  We have been using Radiance and some code Jerry wrote to create
triangular and rectangular polygons.  However the code is not as flexable
as you new gensurf, I'm sure. While your on the line, I would like to ask
you a couple of questions.

I am using Radiance to make images of painted surfaces; panels, cylinders,
etc.  These are included in backgrounds of terrain and trees and used to
get an idea about how well camouflage paints work.  One of the primary
interest is in what are termed gloss levels of the paints.  I think this is
the degree of specularity.  Anyway, the people who make the measurements
record the 'glossyness' as a number from 1 to 1000 using a reflectometer
with fixed angles.  They use black glass as a standard which is defined as
a gloss level of 1000.  Do you have any thoughts on how to relate
specularity and roughness to gloss level, or any literature references that
might be helpful ?  I have been doing the work using extremes of
specularity and roughness to simulate paints at different ends of the gloss
level spectrum.


Another application of Radiance.  I'm also working to try and simulate
surface temperatures of outdoor stuff, landscapes, trees, etc., using
models for conduction and surface energy flux.  One of the biggest
components of the surface energy flux is solar radiation, both direct and
ambient.  I would like to do this for 3-D surface descriptions of the
objects.  I plan to use Radiance to calculate the irradiance at sample
points on the surface of the ground and trees and other things.  I have
made a small modification to rtrace so that I can call it from a C program
with location and surface orientation as arguments and total irradiance as
returned value.  I guess this is not so much of a question as a statement,
but I thought you might have some comments on this.

Thanks for the note on gensurf.  Jerry may have already sent you a request
and if so I can just get a copy from him.  Your software has really been a
boost to our work around here and you sure can't beat the price.  Look
forward to your new releases.   Bye for now.

One last thing, in the off-the-wall category, do you know of any ftp sources
for L-systems software ?



					Randy Scoggins
					US Army Engineer
					Waterways Experiment Station

					scoggins@mc1.wes.army.mil
					

Date: Fri, 31 Jan 92 09:47:17 PST
From: greg (Gregory J. Ward)
To: scoggins@mc1.wes.army.mil
Subject: gensurf and misc.

Hi Randy,

I sent Jerrell a copy of the new gensurf program.  I actually thought of
you folks right away as possible testers, but wasn't sure if you had the
time.

I have only one reference on gloss and how it is measured, and I'm not
sure how to relate it to any physical surface parameters.  The measurement
technique is strictly relative, and doesn't really correlate to anything
but itself.  The fact that it combines overall specular reflectance with
polish is a real problem.  In effect, you have a single measurement where
two are required at the very least.  If you can make some assumptions about
the index of refraction of the material involved, then you may be able to
back this out since specular reflectance can be calculated from Fresnel's law.
What you will discover is that non-metals never have a specularity greater
than .05 or so.

Calling rtrace from a program is quite useful, and I do it in several of my
programs.  You can check out the module ray/src/util/glareval.c and
also ray/src/gen/mkillum2.c.  I use the communication routines in
ray/src/common/process.c to connect to rtrace via dual pipes, so I don't
have to have a separate compiled version of the program.

As for L-systems, I only know of the Mac program made available by Paul
Bourke of New Zealand.  You can pick it up from the pub/mac directory
on hobbes.lbl.gov (128.3.12.38) via anonymous ftp.  I don't know about
source code, but you might try contacting Paul directly.  His e-mail
is  pdbourke@ccu1.aukuni.ac.nz.

Let me know if you have any success with gensurf!

-Greg

Date: Tue, 4 Feb 92 13:59:49 PST
From: Chris Toshok <toshok901@snake.cs.uidaho.edu>
To: greg@hobbes.lbl.gov


  Hi Greg.

   I am working on tracing Newell's teapot using radiance (it would make a 
 very interesting object) but am have trouble understanding how to implement
 bezier patches using gensurf.  I have all the controls points for the patches,
 and they are cubic, which is what gensurf uses (i hope), but I can't figure
 out what the five values gensurf wants for each bezier curve.  I have mapped
 out all the control points onto 4x4 grids which I was going to use, but not
 all the coordinates have the same x,y, or z values.  How can I generate a 
 patch with gensurf when only 5 values can be given for each function x,y and
 z.  Is gensurf capable of producing representations of three dimensional 
 cubic bezier patches? If not, I'll have to write one, and although I am up to
 the task, I would much rather use gensurf.
						Help....
					           Chris 
 

Date: Tue, 4 Feb 92 20:40:03 PST
From: greg (Gregory J. Ward)
To: toshok901@snake.cs.uidaho.edu
Subject: The Teapot

Hi Chris,

The bezier function defined by gensurf is merely the 1-dimensional Bezier
polynomial.  It is up to you, the user, to make it into a 2-dimensional
patch and give it the control points.  This is not too difficult to do,
provided that you know something about the language that gensurf (and
many other programs in Radiance) use.  Unfortunately, I haven't documented
the language very well, so here are some pointers.

Start with the following file to define a 3-dimensional bicubic Bezier
surface in terms of the 1-dimensional Bezier polynomial:
::::::::::
bezier.cal
::::::::::
{
	Bicubic Bezier Patch

	02Mar90

	Define Px(i,j), Py(i,j), Pz(i,j)
}

x(s,t) = bezier(P2x(s,1), P2x(s,2), P2x(s,3), P2x(s,4), t);
y(s,t) = bezier(P2y(s,1), P2y(s,2), P2y(s,3), P2y(s,4), t);
z(s,t) = bezier(P2z(s,1), P2z(s,2), P2z(s,3), P2z(s,4), t);

P2x(s,j) = bezier(Px(1,j), Px(2,j), Px(3,j), Px(4,j), s);
P2y(s,j) = bezier(Py(1,j), Py(2,j), Py(3,j), Py(4,j), s);
P2z(s,j) = bezier(Pz(1,j), Pz(2,j), Pz(3,j), Pz(4,j), s);

{ I have commented out the definition of the Bezier polynomial below, since it
	is defined internally by gensurf and executes a little faster there. }
{
bezier(p1, p2, p3, p4, t) = 	p1 * (1+t*(-3+t*(3-t))) +
				p2 * 3*t*(1+t*(-2+t)) +
				p3 * 3*t*t*(1-t) +
				p4 * t*t*t ;
}
_EOF_

Then, you must create a separate file for each bicubic patch on the teapot,
using the following format:
::::::::::
patchN.cal
::::::::::
{
	Bicubic Bezier patch number N
}
Px(i,j) = select((i-1)*4+j,		{ first index major, second minor }
	3.51, 89.218, 15.38, 17.38,
	5.81, 83.11, 19.635, 14.91,
	6.38, 75.83, 25.183, 18.18,
	7.91, 70.31, 22.83, 19.83
	);
Py(i,j) = select((i-1)*4+j,
	{ 16 more Bezier points }
	);
Py(i,j) = select((i-1)*4+j,
	{ and another 16 }
	);
_EOF_

You'll notice that it is necessary to manipulate the data in order to get
the points in a form that can be easily digested by gensurf.  A short
C program should do the trick.

Once you have all your patch files together, you can create the actual
Radiance input file for the teapot, which will look something like this:
::::::::::
teapot.rad
::::::::::
#
# The (in)famous Utah Teapot
#

void metal copper
0
0
5 .8 .5 .02 .9 0

!gensurf copper patch1 'x(s,t)' 'y(s,t)' 'z(s,t)' 8 8 -s \
		-f bezier.cal -f patch1.cal

!gensurf copper patch2 'x(s,t)' 'y(s,t)' 'z(s,t)' 8 8 -s \
		-f bezier.cal -f patch2.cal

!gensurf copper patch3 'x(s,t)' 'y(s,t)' 'z(s,t)' 8 8 -s \
		-f bezier.cal -f patch3.cal

# and so on...
_EOF_

The -s option to gensurf will create smoother-looking patches by using
Phong surface normal interpolation.  You may also want to create this
file using a C program.

Let me know if I can be of any further assistance.
-Greg

==================================================================
ALIASING

From: Nick (Nikolaos) C. Fotis <nfotis@theseas.ntua.gr>
Subject: Various
To: gjward@lbl.gov (Greg Ward)
Date: Mon, 10 Feb 92 3:56:26 EET

Dear Mr. Ward,

as I finished the last exam for the semester, I anxiously proceeded
to our beloved (except that awful keyboard!) Snake to test your code.

I tried the H-P oriented malloc(). It seems to work fine!
Don't know about speed, though. It's faster than the old way?
I hope to test the same malloc.c with the DECstations we have here.

(And the new gensurf has compiled ok, but I still don't know how to use it!
 ie. How I supply the height field data to this module??)

a. I had  a small problem:

nfotis@kentayros
10:43pm  114   /usr/tmp/nfotis/ray/obj/office > make 
        oconv model.b90 desk misc > modelb.oct
xform: (cornerdesk.norm): bad brightfunc "ygrain"
oconv: fatal - (!xform -e -s 4 -ry 90 -t -28 15.5 28 cornerdesk.norm): bad arguments for brightfunc "ygrain"
*** Error code 1

----

I had to change the relative line in cornerdesk.norm, from
2 ygrain woodpat.cal -s .05
to
4 ygrain woodpat.cal -s .05

---
and everything seemed to work OK here (I suppose)
(your wood texture seems better than the previous - I may be wrong of course!)

b. I feel uneasy about the texture example. In particular, the text is not
very clean, and I feel that it has to do with the way your code samples
intensities across surfaces (I don't really know, since I just use the
system). Also the orange ball seems rather strange.
Perhaps I should send you a UUencoded image??

c. About oversampling and then postfiltering the results:
The idea is rather sound, but some hard spots remain, like venetian
blinds. Perhaps the ray-tracer could get a jittered  sampling option?
(These blinds tend to show some VERY annoying staircase-like patterns,
 even if I use pfilt with -r 0.7 and slash by 3 the resolution of the
 original image :-( )

Another trouble spot seems to be the text rendering in general. Maybe
I'll try to transfer to PAL video tape the filtered images (or at least
to see them on a 24-bit device!)

d. I'm constructing a Frequently Asked Questions message for the
comp.graphics USENET newsgroup, and I would like to include a 1-2
paragraph description of the system. Here's the present description:

RADIANCE 2.0:
------------
In a short sentence, It's a ray-tracer with radiosity effects.
I'm using it on a HP 9000/720, and it's different from the rest
(If you've seen radiosity-generated images, you know what I mean)

Clearly, this doesn't do justice to your program! ;-)

e. I would like for a copy of your theoretic works (from the tail of the
   ray.1 manual):

Ward, G.,  ``Adaptive  Shadow  Testing  for  Ray  Tracing,''
Second Annual Eurographics Workshop on Rendering, to be pub-
lished by Springer-Verlag, May 1991.

Ward, G., ``Visualization,'' Lighting  Design  and  Applica-
tion, Vol. 20, No. 6, June 1990.

Ward, G., F. Rubinstein, R. Clear, ``A Ray Tracing  Solution
for  Diffuse  Interreflection,'' Computer Graphics, Vol. 22,
No. 4, August 1988.

Ward, G., F. Rubinstein,  ``A  New  Technique  for  Computer
Simulation   of   Illuminated   Spaces,''   Journal  of  the
Illuminating Engineering Society, Vol.  17,  No.  1,  Winter
1988.

I would be grateful if you could send me a copy.

Greetings,
Nick.


-- 
Nikolaos Fotis			National Technical Univ. of Athens, Greece
16 Esperidon St.,		UUCP:	mcsun!ariadne!theseas!nfotis
Halandri, GR - 152 32		or InterNet : nfotis@theseas.ntua.gr
Athens, GREECE			FAX: (+30 1) 77 84 578

Date: Mon, 10 Feb 92 09:43:08 PST
From: greg (Gregory J. Ward)
To: nfotis@theseas.ntua.gr
Subject: Re:  Various

Hi Nick,

The new version of malloc should be as fast or faster than anyone else's
implementation, with more efficient memory use for my programs.

Try following the example at the end of the new gensurf man page to
generate a height field.  If it is still confusing to you, I would be
happy to answer specific questions.

a.  Yes, this problem was the result of a careless change I made when
going over to the new woodgrain.  You fixed it correctly, and the fix
has been included in the pub/patch directory on hobbes.

b.  The orange ball in the texture example is meant to appear as an orange.
There is a 1 Mbyte image of what the finished scene should look like called
pub/pics/textures.pic.  The orange is an orange, so it has texture and maybe
that's what looks strange to you.  The text needs to be rendered at a high
resolution to come out right, and you may have to set the pixel sampling
rate (-sp) to 1.

c.  The default pixel jittering (-sj) is .67.  You may increase it if you
like as high as 1 (full pixel jittering).  A setting of -sj 0 would mean
no pixel jittering.  As for the staircases you see on venetian blinds,
this may be a result of the floating point color images more than anything
else.  Most software clips the high end of an image as its written out,
before anti-aliasing is performed.  Because Radiance endeavors to represent
the real values involved, where there is extreme contrast the anti-aliasing
is less effective.  Imagine you have the following boundary in a 3x3 pixel
section of your image, representing pixels brightnesses (rather than colors)
as floating point values:

	.361	.365	.380
	.353	.358	1082.
	.345	1085.	1090.

In a standard approach, these values would be clipped before the filtering
takes place, ie:

	.361	.365	.380
	.353	.358	1.00
	.345	1.00	1.00

The pixels would then be averaged together (assuming 3x3 box filtering) to
a single pixel value, namely .574.  In Radiance, however, no such clipping
takes place, and the correct average of 362 is computed.  To display this
value, we must necessarily clip, but at least we clip to one instead of
the erroneous value of .574.  Also, the resulting filtered image can be
scaled in brightness and the result will still be correct -- not true in
the clipped-then-averaged case.

However, there is a drawback to using correct math in our calculations.
Look at the above pattern of pixels.  What if the pixel sample in the upper
right had landed on the brighter surface rather than the darker surface?
This is quite possible when using jittered sampling.  Our value may then
have been around 1000 rather than .380, and our correct average would
jump from being 362 to 473.  Imagine another case where just one pixel
in our 3x3 grid is that bright -- this amounts to a huge source of
uncertainty in the final value.  With the incorrect clip-then-average
scheme, such large pixel values are never a problem because the result
is always clipped to a value less than one.

In short, if a smooth image is more important to you than a correct one,
you can take the original high-resolution image out of rpict, convert it
to some 24-bit image type (like TIFF or TARGA), and read it into another
program such as Adobe's Photoshop to perform the anti-aliasing on the
clipped image.  If you don't have Photoshop, then I can show you how to
do it with pcomb, but it's much slower.

As for text rendering, the problem is probably that you need to increase
the pixel sampling rate as mentioned before in order to correctly resolve
the text.  Set -sp to 1 and see if that doesn't solve your problem.  By
the way, text looks better without pixel jittering (-sj 0)!

d.  Yes, that description does seem a bit terse.  Please send me your
description before sending it out, and thanks!

e.  The papers are on the way.

Regarding the animation, it is only camera motion and I picked the
keyframes with rview.

-Greg

From: Nick (Nikolaos) C. Fotis <nfotis@theseas.ntua.gr>
Subject: Re:  Various
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Date: Wed, 12 Feb 92 5:18:01 EET

> Hi Nick,
> 
> Try following the example at the end of the new gensurf man page to
> generate a height field.  If it is still confusing to you, I would be
> happy to answer specific questions.

(blush) I had deleted the previous gensurf you sent after the announcement
of the erroneous part you sent(I had not the time to try it).
Did you include a manual for gensurf in you first post??
Please send it to me again...

> b.  The orange ball in the texture example is meant to appear as an orange.
> There is a 1 Mbyte image of what the finished scene should look like called
> pub/pics/textures.pic.  The orange is an orange, so it has texture and maybe
> that's what looks strange to you.  The text needs to be rendered at a high
> resolution to come out right, and you may have to set the pixel sampling
> rate (-sp) to 1.

It would be nice to have compressed these files, because we're on the Internet
via a Trailbazer+ modem at 9600 (or 19200?) bps.
It could make my life much easier....

In any case, when I tried to display the image, I got an

ximage: fseek error

Do your picture files are byte order indepedent? I fear the answer is no :-(
In any case, I re-rendered the scene with the parameters that you had inside
the image's header (the new rpict didn't like the -dp .9 parameter, so I
just left it out..)

The high-resolution pic was great, so I got assured that there was not
some flaw to the system (It would't be good for you, no?? ;-) )

The trouble spot (or artifact, if you prefer) was the extremely high contrast
of the base surface (white?) with the orange surface that gave to the
orange ball a rather odd appearance.

Perhaps you should use something like Sun's XDR??
I heard that many Unix boxes include these libraries, but I would prefer
something like the free BRL-CAD's library for network file order and
reading/writing these data. You could include it on the Radiance distribution,
making it more immune from changes to its environment.

> c.  The default pixel jittering (-sj) is .67.  You may increase it if you
> like as high as 1 (full pixel jittering).  A setting of -sj 0 would mean

Ahh, I should have RTFMed before I ask such a question!!

> no pixel jittering.  As for the staircases you see on venetian blinds,
> this may be a result of the floating point color images more than anything
> else.  Most software clips the high end of an image as its written out,
> before anti-aliasing is performed.  Because Radiance endeavors to represent
> the real values involved, where there is extreme contrast the anti-aliasing
> is less effective.  Imagine you have the following boundary in a 3x3 pixel
> section of your image, representing pixels brightnesses (rather than colors)
> as floating point values:

Hmmmm... I know that the human eye is not linearly sensitive to the various
brightness levels you present to it. You could do (perhaps) a logarithmic
hack to scale the values to the range 0..255??
But given the VERY wide range possible with FP numbers, I feel it's at best
a challenge...

[etc]
> However, there is a drawback to using correct math in our calculations.
> Look at the above pattern of pixels.  What if the pixel sample in the upper
> right had landed on the brighter surface rather than the darker surface?
> This is quite possible when using jittered sampling.  Our value may then
> have been around 1000 rather than .380, and our correct average would
> jump from being 362 to 473.  Imagine another case where just one pixel
> in our 3x3 grid is that bright -- this amounts to a huge source of
> uncertainty in the final value.  With the incorrect clip-then-average

And I thought that a 3-fold increase in dimensions plus gaussian filtering
would take good care of all these problems... Going to 4-fold sizes is a VERY
expensive proposition (and again, it may be not enough)

> scheme, such large pixel values are never a problem because the result
> is always clipped to a value less than one.
> 
> In short, if a smooth image is more important to you than a correct one,

At this time, I'm interested in artistically "correct" images.
When I take the Photometry course, of course my interests will be the other
way around...
(Your programs made me thinking about it. Seriously!)

> you can take the original high-resolution image out of rpict, convert it
> to some 24-bit image type (like TIFF or TARGA), and read it into another
> program such as Adobe's Photoshop to perform the anti-aliasing on the
> clipped image.  If you don't have Photoshop, then I can show you how to
> do it with pcomb, but it's much slower.

Since we don't have Macintoshes lying around here, I'm forced to the UNIX
route (not that I feel bad about it! ;-) ). And the file transfer to a Mac
is not that fast (ie.sneakernet).

What's your recipe about pcomb??

> As for text rendering, the problem is probably that you need to increase
> the pixel sampling rate as mentioned before in order to correctly resolve
> the text.  Set -sp to 1 and see if that doesn't solve your problem.  By
> the way, text looks better without pixel jittering (-sj 0)!

I had done a 512x512 rendering, and it didn't seem enough. I'll try it later
(when your test anim finishes!
For the anim, I changed the parameters, so I hope to get
PAL-sized images. I filter down to 760x578, the overscan PAL resolution -
If I remember correctly the numbers. I put a horizontal field of view of
50 degrees. Does the vertical fov changes accordingly??? or I have to set
this also?)

> d.  Yes, that description does seem a bit terse.  Please send me your
> description before sending it out, and thanks!

See above. I think there's no problem...
> 
> e.  The papers are on the way.

Many thanks!!

> Regarding the animation, it is only camera motion and I picked the
> keyframes with rview.

OH! And you got the inbetween numbers with rpict. Correct??
(I had not seen this potential inside the manuals. Perhaps you should
 emphasize it in another section? In the other side, I usually play with
 Radiance somewhat strange hours of the day... And so I'm less than
 bright when I look at the manuals)

Greetings,
Nick.

Date: Wed, 12 Feb 92 10:50:35 PST
From: greg (Gregory J. Ward)
To: nfotis@theseas.ntua.gr
Subject: Re:  Various

Hi Nick,

Did you remember to set binary mode before ftp'ing the image?  The Radiance
picture format is byte-order independent, and should read correctly when
transferred between machines.  I'm sorry that I didn't compress the image
beforehand.  All of those images should be kept compressed.  I will do
that now.

The correct scaling of images for viewing is an open research topic.
A recent paper by Tumblin and Rushmeier suggested the following brightness
mapping:

{
	Mapping of Luminance to Brightness for CRT display.
	Hand this file to pcomb(1) with the -f option.
	The picture file should have been run previously through
	the automatic exposure procedure of pfilt(1), and
	pcomb should also be given -o option.  Like so:

	pfilt input.pic | pcomb -f tumblin.cal -o - > output.pic

	If you are using pcomb from Radiance 1.4, you will have
	run without pfilt and set the AL constant manually.  If
	you are using a pcomb version before 1.4, you will have
	to do this plus change all the colons ':' to equals '='
	and wait a lot longer for your results.

	Formulas adapted from Stevens by Tumblin and Rushmeier.

	28 August 1991
}
PI : 3.14159265358979323846;	{ Hmm, looks familiar... }
LAMBERTS : 1e4/PI/179;		{ Number of watts/sr/m2 in a Lambert }
DL : .027;			{ Maximum display luminance (Lamberts) }
AL : .5/le(1)*10^.84/LAMBERTS;	{ Adaptation luminance (from exposure) }

sq(x) : x*x;
aa(v) : .4*log10(v) + 2.92;
bb(v) : -.4*sq(log10(v)) + -2.584*log10(v) + 2.0208;

mult = li(1)^(aa(AL)/aa(DL)-1) * ( 10^((bb(AL)-bb(DL))/aa(DL)) / DL );

ro = mult*ri(1);
go = mult*gi(1);
bo = mult*bi(1);
--------------------------------
You can apply this directly with pcomb as shown in the example.  If you
want to clip the images prior to anti-aliasing reduction with pfilt, just
apply a function such as 'clip(x)=if(x-1,1,x)' using pcomb, ie:

	% pcomb -e 'ro=clip(ri(1));go=clip(gi(1));bo=clip(bi(1))' \
		-e 'clip(x)=if(x-1,1,x)' adjusted.pic \
		| pfilt -x /3 -y /3 -1 -r .67 > final.pic

Note that "adjusted.pic" must already be set to the desired exposure level
with a previous run of pfilt.  Alternatively, if you know the correct
exposure scaling, you can set it with a "-s expval" option to pcomb 
immediately before the original picture.

Regarding your changes to and problems with the animation script, perhaps
you could send it to me.  The vertical field of view is not altered by
the horizontal setting.  Rather, the image height or width is adjusted
down to insure that the specified pixel aspect ratio (if non-zero) is met.
If the aspect ratio (-p option) is set to zero, then you will get exactly
what you ask for in terms of x and y image resolution.

The inbetween frame position are actually calculated by rcalc using the
Catmull-Rolm spline algorithm in spline.cal.  None of this is well-
documented as I have never gotten around to making a nice walkthrough
animation executor.  I believe Paul Bourke and the folks in New Zealand
may be working on one.  (pdbourke@ccu1.aukuni.ac.nz)

-Greg

=============================================================
SHARED_PICTURES

From: Alexander Keith Barber <barber@ravl.rice.edu>
Subject: Rice U Renderings
To: greg@hobbes.lbl.gov
Date: Tue, 11 Feb 92 17:20:07 CST

Greg - 

I just uploaded 3 pictures along with a README in a tar.Z file to the xfer
directory of hobbes.  I hope people will pull them down and view them; I would
like people to see what sort of large scale renderings are possible with
Radiance.  Perhaps you could tell people on the mailing list about these
pictures?  Despite the fact that the .rad file used for these .pics is several
megs, as is the octree, the longest rendering time was one and a half hours.
The shortest time was a quarter hour for a 512x512 version of the large aerial
view included here.  I just love the processing speed of a Unix platform.  I
hate to think how long these would take in Autocad...  I've seen _hidden line_
drawings alone take hours...

Alex Barber
barber@comet.rice.edu


Date: Tue, 11 Feb 92 17:38:45 PST
From: greg (Gregory J. Ward)
To: barber@ravl.rice.edu
Subject: Re:  Rice U Renderings

Hi Alex,

Thanks for your contributions.  I would like to encourage more such
contributions from others, but I'm not sure I have enough disk space to
hold them.  

Generally, I only ask people who want to share to share the .rad files
in compressed format, since these usually take up less space.  In your
case, though, I'm not so sure!

I'm curious why you didn't use the rendering capabilities built into AES?
I was wondering also if you and Dwayne might be willing to share your
file converter with the rest of the world?

I am eager to take a look at your pictures myself.  Unfortunately, I'm
at home now and output on a dot matrix printer just doesn't cut it.

I'm glad that you have had such success with Radiance.  It's true of any
good ray tracing program that it will be faster with large models than
any object rendering technique such as z-buffer or hidden line algorithms.
You should get ahold of version 2.0, though.  It really is much better
than previous releases in a number of ways.  Version 2.1 will even be
able to render models twice as large in the same amount of memory (with
some loss in geometric accuracy).

-Greg

From: Alexander Keith Barber <barber@ravl.rice.edu>
Subject: Re:  Rice U Renderings
To: greg@hobbes.lbl.gov (Gregory J. Ward)
Date: Wed, 12 Feb 92 9:48:39 CST

Greg -

In reply to:

>I'm curious why you didn't use the rendering capabilities built into AES?
>I was wondering also if you and Dwayne might be willing to share your
>file converter with the rest of the world?

I must say that while we have had no problems making hidden line and hidden
surface pictures, using surface definitions of our own in AES, as well as a
light source for a sun, there are still a few problems creating raytraced
output with AES.  In other words, I have no output that makes any sense.  No
matter what I try, I end up with a light source too bright, too dark, too
focused like a spotlight... Despite following the tutorial and manual to the
letter, I have nothing but a a couple meg of various small pictures that are
rather fun for the mood they create (a spotlight against a building in the
dark, creating purple shadows) but that have nothing to do with realism.  Hence
our use of Radiance to do renderings...


>You should get ahold of version 2.0, though.  

That is what we have been using since you released it.  We still have some 
problems with Radiance and surface defs, tho'.  I'll send you a few pictures - 
small ones - that illustrate our difficulties.  I'll render a building I've
created, using just gensky for light (no ground glow since I have a large plane
I use as grass or concrete or whatever).  The resultant picture is very nice,
but I'll get a blue color thrown on the building from the sky, along with the
green of the ground...  I'll send you details later this week.

Alex Barber
barber@comet.rice.edu

Date: Wed, 12 Feb 92 10:21:42 PST
From: greg (Gregory J. Ward)
To: barber@ravl.rice.edu
Subject: Re:  Rice U Renderings

Hi Alex,

I finally got a look at your images.  Very nice.  I have shrunk the first
one to 512x512 using pfilt and put it in the pub/pics directory for sharing
along with your README file.

I misread the header on your images and concluded (wrongly) that you were
still using an earlier version.  Sorry.  Your sky does look a little too
blue to me, and that may be why you get more color bleeding than you would
like on your renderings.  If you upload them, I will be able to say for sure.

You may still want to create a ground source for your scene, so that the
horizon does not appear black.

-Greg

====================================================================
AMIGA_PORT

Date: Thu, 13 Feb 92 17:12:41 +0100
From: bojsen@id.dth.dk (Per Bojsen)
To: greg@hobbes.lbl.gov
Subject: Amiga port of Radiance 2.0, beta version

Hi Greg,

I've uploaded a beta version of the Amiga port of Radiance in the
/pub/ports/amiga directory.  The archive is in the `lharc' format.
`Lharc' is a popular archiving/compressing utility, which is available
for the IBM PC, Amiga, and UNIX.  Is it OK, that I use this format?

The archive contains binaries, the library files, the example
objects/models, and documentation.  No source.  When I release the
final version of the port I'll upload a diff of the sources as I
believe you requested.

-- 
Per Bojsen         The Design Automation Group     Email: bojsen@ithil.id.dth.dk
MoDAG            Technical University of Denmark          pb@id.dth.dk


Date: Thu, 13 Feb 92 08:33:59 PST
From: greg (Gregory J. Ward)
To: bojsen@id.dth.dk
Subject: Re:  Amiga port of Radiance 2.0, beta version

Hi Per,

Thank you for uploading the port.  Does this lharc utility come standard
with the Amiga?  If not, can you legally upload a program to unarchive the
files?  If not, than it might be better to use the archiving utility I
wrote, which can be freely distributed.  I suspect that it has close to
the same utility as lharc, though I know nothing of this program.

I have ported my file archiving/compression programs (pkg and unpkg) to
UNIX, MS-DOS and C/PM.  I do not have a version for the MacIntosh or the
Amiga, though I suspect porting it to the Amiga would be a snap.  I'll
be happy to provide you with the source code if you need it.

Thanks again!
-Greg

===================================================================
DECSTATION

Date: Thu, 13 Feb 1992 13:15 EDT
From: RCBI110@MARSHALL.MU.WVNET.EDU
Subject: Re:  Radiance install question
To: greg@hobbes.lbl.gov

Greg,

 Somehow I magically got all the programs, and I don't know how I did it...:^)

Today's question: error message:

rview: Cannot open command line window

I get a nice blank black window for about 2 seconds then it stops with this
error message...
If it matters, it's on a brand new DECsystem 5000/200. Fresh out of the box,
almost :^)

Any suggestions??

Alan

Date: Thu, 13 Feb 92 10:23:59 PST
From: greg (Gregory J. Ward)
To: RCBI110@MARSHALL.MU.WVNET.EDU
Subject: Re:  Radiance install question

Yes, I think that other DECstation users have had similar problems, because
DEC for some reason does not see fit to distributing the standard X11 fonts
with its system.  You must reset the COMFN macro in ray/src/rt/x11.c to
a font that is supported on your system.  I don't know what that would
be, but there's got to be something.  Also, you will have to change COMCW
and COMCH while you are at it.

Likewise, you should make a similar change to the FONTNAME macro in
ray/src/px/x11image.c and ray/src/util/xglaresrc.c.

I hope this solves your problem!
-Greg

Date: 20 Feb 92 15:00:00 PST
From: "Jack Hsiung" <cvetp035@CSUPomona.Edu>
Subject: Re:  Problem making obj/office with Radiance 2.0
To: "greg" <greg@hobbes.lbl.gov>

I followed your advice and changed the 8x13 font in src/rt/x11.c and
src/px/x11image.c to fixed (works for other X windows programs on
this DECstation). Now rview and ximage are able to display the images.
However, it seems that images displayed by ximage have their red and
blue channels switched. For example, the reddish looking wood looks blue.

rview displays the colors fine. Any idea what can be causing this?

Jack

Date: Thu, 20 Feb 92 15:04:23 PST
From: greg (Gregory J. Ward)
To: cvetp035@CSUPomona.Edu
Subject: Re:  Problem making obj/office with Radiance 2.0

Hi Jack,

Do you have a 24-bit X11 server?  There doesn't seem to be much of agreement
on how these beasties are supposed to work.  I don't have one myself, so
it is difficult for me to debug from here.

If your X11 server is only 8-bit, then we're in a heap of trouble!

Couldn't you find some way to get it to find the more standard font?

-Greg

Date: 20 Feb 92 15:21:00 PST
From: "Jack Hsiung" <cvetp035@CSUPomona.Edu>
Subject: Re:  Problem making obj/office with Radiance 2.0
To: "greg" <greg@hobbes.lbl.gov>

I know the display is 24-bit and the server is DEC's own, which I think
is 24-bit (The colors in the demo animation blends very smoothly).

Is it possible to go into the code and switch the red and blue when
ximage reads an image?

I'll try to figure out how to get the 8x13 font to work.

Jack

Date: Thu, 20 Feb 92 15:37:17 PST
From: greg (Gregory J. Ward)
To: cvetp035@CSUPomona.Edu
Subject: Re:  Problem making obj/office with Radiance 2.0

Go to line 733 of x11image.c.  There, you can reverse the ordering of
those three statements and that should turn the trick.  It's a bad hack,
though, since the server should be doing this job in XImage().

==============================================================
INFRARED

Date: Thu, 20 Feb 92 15:58:12 +0100
From: manolesc@cethil.univ-lyon1.fr
Subject: Infrared radiance
To: greg@hobbes.lbl.gov

   Hi, Greg !

   Here I am again bothering you with questions about infrared radiance.
   I am not sure to make a good connection of the radiance curve with the rgb va
lues. So :

   1 In wich file do you fix the 3 representative wavelengths rgb emploied by
     RADIANCE ?
   
   2 The units of mesure for the rgb radiance values of the "light" material
     are Watts/rad2/m2 or Watts/sr/m2 ? 
     If Watts/rad2/m2 how do you calculate "rgb" knowing the 3 wavelengths fixed     on the 1st point ?

   3 The "l" comand in XIMAGE displays the luminance value in the area of 
     interest. In what unit of mesure is it displayed ?

   Thanks a lot for everything, Mircea.

Mircea Manolescu
INSA Lyon- Batiment 307
21, Av. Albert Einstein
69126 Villeurbanne
E-mail: manolesc@cethil

Date: Thu, 20 Feb 92 08:53:34 PST
From: greg (Gregory J. Ward)
To: manolesc@cethil.univ-lyon1.fr
Subject: Re:  Infrared radiance

Hello Mircea,

I will try to answer your questions as best I can.

   1 In wich file do you fix the 3 representative wavelengths rgb emploied by
     RADIANCE ?

As I think I said before, there are no specific wavelengths employed by
Radiance for red, green and blue.  Those three channels can mean whatever
you want them to mean, and they are treated identically throughout the
calculation.  The only time any assumption is made about them is by
ies2rad to compute a lamp color or ximage to compute luminance.  In most
applications, these primaries are chosen to correspond to a standard
computer monitor, but this may be totally inappropriate in your application.

   2 The units of mesure for the rgb radiance values of the "light" material
     are Watts/rad2/m2 or Watts/sr/m2 ?
     If Watts/rad2/m2 how do you calculate "rgb" knowing the 3 wavelengths fixed
     on the 1st point ?

I am afraid I don't know what you mean by "rad2" or how this differs from
steradians.  The units for light sources are Watts/sr/m2/spectrum, where
"spectrum" is the totality of wavelengths in which you are interested.
In other words, the value for a particular channel for a light source is
given as the total Watts/sr/m2 that source would have over the spectrum
if it emitted uniform white light at that level.  The reason for giving
such values rather than the more usual Watts/sr/m2/channel is so the
values are independent of the wavebands selected for the channels.  A
value of "1 1 1" will always mean uniform white light over the desired
spectrum with a total radiance of 1 Watt/sr/m2.

   3 The "l" comand in XIMAGE displays the luminance value in the area of
     interest. In what unit of mesure is it displayed ?

The unit of luminance used is candelas/m2 (lumens/sr/m2), and the conversion
factor from Watts/sr/m2 is 179, which is the luminous efficacy of white
light over the visible spectrum (380nm to 780nm).  This is the default
efficacy used by Radiance, although again you may find it to be inappropriate
for your needs.

I hope this helps.  Please don't hesitate to ask any further questions you
might have.

-Greg

===========================================================
SPECULARITY_BUG

Date: Thu, 16 Apr 92 08:12:50 EDT
From: spencer@cgrg.ohio-state.edu (Stephen Spencer)
To: greg@hobbes.lbl.gov
Subject: Can you help?

One of our users has a well-documented case of version 1.4 producing far
better results when compared to version 2.0 of the RADIANCE software.
I've uploaded a file, "forWard.tar.Z", into the pub/xfer area of your 
machine -- can you look at it for me/him?

If you could, send the replies to 

	spencer@cgrg.ohio-state.edu

and to

	ksimon@cgrg.ohio-state.edu

as he (Kevin) is the user in question.

Thanks very much!

steve 

Date: Thu, 16 Apr 92 12:28:59 PDT
From: greg (Gregory J. Ward)
To: ksimon@cgrg.ohio-state.edu, spencer@cgrg.ohio-state.edu
Subject: Re:  Can you help?

Dear Steve and Kevin,

I have looked at your images and your files and what you are seeing is
the difference in the way Radiance 2.0 handles specular surfaces.  Simply
put, version 1.4 was not fully able to compute reflection from specular
surfaces.  Radiance 2.0 does a much better job.  However, most of the
surfaces in your room should be completely diffuse, yet the input file
defines these materials as having a specularity between 1% and 10%.
In my current model of specular surfaces, the degree of specularity
increases near grazing angles.  Thus, even a specularity of a few
percent will increase close to 1 near grazing.  That is what is
causing the unusual bright areas at the base of your furniture, in
the corners of the room, etc.  It is also causing a "sheen" in your
sofas that is quite unnatural.

This gives me reason to reconsider my calculation of the specular
component near grazing, to be sure.  The lesson for your work is
not to specify a specular component unless you really mean it!
Most fabrics and wall coverings and paints are diffuse.  Enamel
paint, formica, and other plastic-like finishes may have some
specularity, but never more than a few percent.  Only metals have
a significant specular component.

Hope this helps.  Thanks very much for bringing this to my attention!

-Greg

Date: Mon, 20 Apr 92 09:33:27 PDT
From: greg (Gregory J. Ward)
To: spencer@cgrg.ohio-state.edu
Subject: Re:  Can you help?
Cc: ksimon@cgrg.ohio-state.edu

Dear Steve (and Kevin),

Actually, the problem you noticed in 2.0 was a rather serious bug in the
normalization of the specular reflection from light sources.  I am
eternally grateful that you brought this to my attention, as I was just
about to send in a Siggraph paper with the wrong formula!!  Thanks to
you, I won't have to publish a retraction and go around hanging my
head low the rest of my days!

I can send you the repaired files if you like, or you can wait for this
and other bug fixes in version 2.1, due out soon.

Thanks again!
-Greg

Date: Mon, 20 Apr 92 12:52:14 EDT
From: spencer@cgrg.ohio-state.edu (Stephen Spencer)
To: greg@hobbes.lbl.gov
Cc: ksimon@cgrg.ohio-state.edu
Subject:  Can you help?

Glad to hear that we've helped.

How soon is "due out soon"?  I think we can probably just wait... (Kevin, I'm
not trying to speak for you here.)

steve

=============================================================
VIEW_INFO

Date: Tue, 21 Apr 92 16:33:04 +0100
From: andre@borneo.inet.dkfz-heidelberg.de (Andre Schroeter)
To: gjward@Csa1.lbl.gov
Subject: radiance

hallo,
i just compiled radiance v2.0 on ISC2.2.
all works fine exept xshowtrace and the *glare* programs.
these programms only show an errormessage that they can't get the view from
the pic. ximage beeps if i try to get information with the 't'command.
maybe you know what's going wrong ???

thanks andre

e-mail: andre@borneo.inet.dkfz-heidelberg.de
        81239@rz.novell1.fht-mannheim.de

Date: Tue, 21 Apr 92 09:09:32 PDT
From: greg (Gregory J. Ward)
To: andre@borneo.inet.dkfz-heidelberg.de
Subject: Re:  radiance

The problem must be with your picture file.  Run getinfo on it and send
me the output.  (Xshowtrace and glare only work with rpict and pfilt output.)

-Greg

To: greg@hobbes.lbl.gov
From: "Andre Schroeter"  <81239@novell1.rz.fht-mannheim.de>
Date:     28 Apr 92 07:48:45 GMT+0100
Subject:  RE: problem with view in picfile

hallo,
here is the output of getinfo. this picture is the fisheye view from the
example in the tutorial manpage.


fish.pic:
	/usr/andre/radiance/oconv sky.rad outside.rad mkiwindow.rad room.rad 
	/usr/andre/radiance/rpict -vta -vp 1.5 .8 1 -vd 0 1 0 -vh 240 -vv 180 -av .5 .5 .5 
	SOFTWARE= RADIANCE 2.0 lastmod Thu Apr 16 21:43:22 MES 1992 by andre on andre
	FORMAT=32-bit_rle_rgbe

thanks, andre

e-mail: andre@borneo.inet.dkfz-heidelberg.de
        81239@rz.novell1.fht-mannheim.de
	

Date: Mon, 27 Apr 92 23:16:03 PDT
From: greg (Gregory J. Ward)
To: 81239@novell1.rz.fht-mannheim.de
Subject: RE: problem with view in picfile

Hi Andre,

The problem is that you are using an explicit path to rpict (starting with
a '/'), which ximage and xshowtrace do not know how to read.  This is a
bug that I really ought to fix...  I will attempt to do so and send you
a patch a little later.

-Greg

Date: Tue, 28 Apr 92 11:17:20 PDT
From: greg (Gregory J. Ward)
To: 81239@novell1.rz.fht-mannheim.de
Subject: RE: problem with view in picfile
Status: R

I have made the changes, but it is probably better to wait for release 2.1
since I had to change several files.  I will release 2.1 next month sometime.

-Greg

=======================================================
BACKGROUND_COLOR

Date: Mon, 27 Apr 92 12:17:57 -0400
From: David Jones  <djones@lightning.McRCIM.McGill.EDU>
To: greg@hobbes.lbl.gov
Subject: background color instead of black??


Hi Greg, I'm trying to generate some RADIANCE pics really quickly.
I'd like to render an incomplete scene, and color any ray that does not
hit an object as GREY instead of BLACK as rpict does by default.
Is there any easy way to do this, or to massage the output of rpict?

dj

Date: Mon, 27 Apr 92 09:28:02 PDT
From: greg (Gregory J. Ward)
To: djones@lightning.McRCIM.McGill.EDU
Subject: Re:  background color instead of black??

Hi Dave,

Just make a glow source with the desired color, like so:

void glow background_color
0
0
4 .2 .3 .4 0

background_color source background
0
0
4 0 0 1 360

-Greg

Date: Mon, 27 Apr 92 09:30:14 PDT
From: greg (Gregory J. Ward)
To: djones@lightning.McRCIM.McGill.EDU
Subject: Re:  background color instead of black??

You can also massage the output picture using pcompos:

	pcompos -b .2 .3 .4 -t 1e-4 input.pic 0 0 > output.pic

Note that any pixel values less than 1e-4 will be replaced by the
background color, so this is no good if you actually have black objects
in your scene.

===============================================================
UPFRONT_TRANSLATOR

Date: Fri, 1 May 92 17:42:59 NZT
From: pdbourke@ccu1.aukuni.ac.nz
Subject: For your information
To: GJWard@lbl.gov

I have just written a model translator from Alias Upfront on the Macintosh
to Radiance. It seems to work really well. Layers are colours are converted
into materials. If anyone is interested then you can pass my address on
otherwise I will eventually install a copy on your site. At the monent you
only get 3 or 4 point facets (upfront limitation) but I intend to do cleaver
tests and convert appropriate things into genbox and genprism calls. 
------------------------------
Paul D. Bourke                             School of Architecture
pdbourke@ccu1.aukuni.ac.nz                 Auckland University
         (130.216.1.5)                     Private Bag
Ph:  +64 -9 373 7999 x7367                 Auckland
Fax: +64 -9 373 7410                       New Zealand

============================================================
SCENE_FLATTENING

Date: Mon, 4 May 92 10:01:52 NZT
From: pdbourke@ccu1.aukuni.ac.nz
Subject: Radiance extraction
To: GJWard@lbl.gov

Is there a way to extract a decomposed description of a Radiance scene
description, that is,  a file containing just primitives such as polygons,
spheres etc (no generators) I have tried various methods but have not found
a way that doesn't require a possibly high user input.
------------------------------
Paul D. Bourke                             School of Architecture
pdbourke@ccu1.aukuni.ac.nz                 Auckland University
         (130.216.1.5)                     Private Bag
Ph:  +64 -9 373 7999 x7367                 Auckland
Fax: +64 -9 373 7410                       New Zealand


Date: Sun, 3 May 92 21:17:46 PDT
From: greg (Gregory J. Ward)
To: pdbourke@ccu1.aukuni.ac.nz
Subject: Re:  Radiance extraction

Hi Paul,

That's great news about the UpFront! translator!.  I wish I had this program,
so I could use the translator.

Regarding expanded Radiance descriptions, you can use xform with the -e
option to take out all inline commands, like so:

	% xform -e input.rad > expanded.rad

I have considered from time to time writing a program to completely polygonize
a scene description, replacing all spheres and cones and even bringing in
instances and converting everything to polygons, but I have never had a
real need to do it so have just left it as an idea for a rainy day.

-Greg