1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!--Converted with LaTeX2HTML 2002-2-1 (1.71)
original version by: Nikos Drakos, CBLU, University of Leeds
* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
* with significant contributions from:
Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
<HTML>
<HEAD>
<TITLE>Stars and Catalogs</TITLE>
<META NAME="description" CONTENT="Stars and Catalogs">
<META NAME="keywords" CONTENT="gcx">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<META NAME="Generator" CONTENT="LaTeX2HTML v2002-2-1">
<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">
<LINK REL="STYLESHEET" HREF="gcx.css">
<LINK REL="next" HREF="node6.html">
<LINK REL="previous" HREF="node4.html">
<LINK REL="up" HREF="gcx.html">
<LINK REL="next" HREF="node6.html">
</HEAD>
<BODY >
<DIV CLASS="navigation"><!--Navigation Panel-->
<A NAME="tex2html548"
HREF="node6.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
SRC="/usr/share/latex2html/icons/next.png"></A>
<A NAME="tex2html544"
HREF="gcx.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
SRC="/usr/share/latex2html/icons/up.png"></A>
<A NAME="tex2html538"
HREF="node4.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
SRC="/usr/share/latex2html/icons/prev.png"></A>
<A NAME="tex2html546"
HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
SRC="/usr/share/latex2html/icons/contents.png"></A>
<BR>
<B> Next:</B> <A NAME="tex2html549"
HREF="node6.html">World Coordinates</A>
<B> Up:</B> <A NAME="tex2html545"
HREF="gcx.html">GCX User's Manual</A>
<B> Previous:</B> <A NAME="tex2html539"
HREF="node4.html">Image Files</A>
<B> <A NAME="tex2html547"
HREF="node1.html">Contents</A></B>
<BR>
<BR></DIV>
<!--End of Navigation Panel-->
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
<UL CLASS="ChildLinks">
<LI><A NAME="tex2html550"
HREF="node5.html#SECTION00510000000000000000">Star Detection</A>
<LI><A NAME="tex2html551"
HREF="node5.html#SECTION00520000000000000000">Loading Catalog Stars</A>
<UL>
<LI><A NAME="tex2html552"
HREF="node5.html#SECTION00521000000000000000">Object Catalogs</A>
<LI><A NAME="tex2html553"
HREF="node5.html#SECTION00522000000000000000">Field Star Catalogs</A>
</UL>
<BR>
<LI><A NAME="tex2html554"
HREF="node5.html#SECTION00530000000000000000">Star Files</A>
<UL>
<LI><A NAME="tex2html555"
HREF="node5.html#SECTION00530010000000000000">GSC-2 files</A>
<LI><A NAME="tex2html556"
HREF="node5.html#SECTION00530020000000000000">Native format files</A>
<LI><A NAME="tex2html557"
HREF="node5.html#SECTION00530030000000000000">Other star files</A>
</UL>
<BR>
<LI><A NAME="tex2html558"
HREF="node5.html#SECTION00540000000000000000">Setting up Catalogs</A>
<UL>
<LI><A NAME="tex2html559"
HREF="node5.html#SECTION00541000000000000000">Setting up GSC</A>
<LI><A NAME="tex2html560"
HREF="node5.html#SECTION00542000000000000000">Setting up Tycho2</A>
<LI><A NAME="tex2html561"
HREF="node5.html#SECTION00543000000000000000">Setting up Object Catalog Files</A>
</UL></UL>
<!--End of Table of Child-Links-->
<HR>
<H1><A NAME="SECTION00500000000000000000"></A><A NAME="ch:stars"></A>
<BR>
Stars and Catalogs
</H1>
<P>
In addition to images, <SMALL>GCX </SMALL>handles lists of astronomical objects generally referred to as
<EM>stars</EM>. There are several types of stars, and the various types have different kinds of
information attached. They can be grouped in two classes:
<OL>
<LI><EM>Frame stars</EM> only have positions within a frame (pixel coordinates). They come
into existence by detection, either automatic, or user-directed. There are three
sub-types of frame stars:
<UL>
<LI>detected stars;
</LI>
<LI>user stars;
</LI>
<LI>aligment stars.
</LI>
</UL>
</LI>
<LI><EM>Catalog stars</EM> have world coordinates (right ascension and declination) attached to them,
and can also hold photometric information. Catalog stars are either read from a catalog or recipe
file, or created interactively by editing another star. There are four sub-types of catalog stars:
<UL>
<LI>fields stars;
</LI>
<LI>catalog objects;
</LI>
<LI>standard stars;
</LI>
<LI>photometry targets (AP targets).
</LI>
</UL>
</LI>
</OL>
Stars are drawn on top of the displayed images. The apearance of the
various types of stars can be changed using the options under <EM>Star
Display Options</EM>.
<P>
<H1><A NAME="SECTION00510000000000000000"></A><A NAME="sec:stardet"></A>
<BR>
Star Detection
</H1>
<P>
A relatively straight-forward star detection algorithm is implemented in <SMALL>GCX.</SMALL>
It will search for
local intensity peaks that satisfy the following conditions:
<OL>
<LI>The peak is higher than the local background plus a specified number of standard deviations
(usually 6-9). The number of standard deviations is specified in the <EM>Star Detection SNR</EM>
option;
</LI>
<LI>There are at least 4 pixels adjacent to the peak which are above the threshold;
</LI>
<LI>The peak is not too close to another, higher peak;
</LI>
<LI>The star radius (are in which the star is above the background) isn't too large;
</LI>
</OL>
The <EM>Maximum Detected Stars</EM> parameter limits the number of stars that are detected.
The whole frame is searched and the bightest stars are kept.
<P>
The star detection routine is called by selecting <EM>Stars/Detect Sources</EM>, or
automatically by other operations (WCS fitting and frame
alignment). The detection routine will produce <EM>detected stars</EM>,
except when called on an alignment reference frame, in which case it
will produce <EM>alignment stars</EM>.
<P>
Another way of creating frame stars is to control-click on or near an
otherwise unmarked star image. This will initiate a spiral star search in a
region around the the cursor, with the SNR parameter set to a low
value (3.0). In this way, even very faint stars that are located near
the cursor can be marked. This procedure creates <EM>user stars</EM>.
<P>
<H1><A NAME="SECTION00520000000000000000">
Loading Catalog Stars</A>
</H1>
<P>
As their name implies, catalog stars are generally loaded from catalog
files. <SMALL>GCX </SMALL>supports three kinds of catalogs: object catalogs, from
which the stars are loaded by name (like GCVS, NGC, Messier, IC);
field star catalogs, from which the stars are loaded by region of
interest; and star files (including recipe files), which are loaded in
their entirety, as they presumably contain stars in a region of
interest.
<P>
As catalog stars are located by world coordinates, the program cannot
display any of them if it doesn't have at least an approximate idea
of what the image's coordinates are in the real world. The frame must
have at least an <EM>initial WCS</EM>.<A NAME="tex2html10"
HREF="footnode.html#foot252"><SUP><SPAN CLASS="arabic">4</SPAN>.<SPAN CLASS="arabic">1</SPAN></SUP></A>
<P>
If the frame WCS is unset, the program will refuse to load field
stars; it will set the initial WCS so that the loaded object is at
the center of the frame if a single object is loaded from an object
catalog; and it will refuse to load a star file, unless the star file is
a recipe that contains target coordinates, in which case the initial
WCS will be set from those coordinates.
<P>
<H2><A NAME="SECTION00521000000000000000">
Object Catalogs</A>
</H2>
Two formats for object catalogs are currently supported: the <TT>.edb</TT> format, also used by XEphem, and the <TT>.gcx</TT> format. The two
are treated differently: <TT>.gcx</TT> files can be loaded in memory and
the whole set searched by name; <TT>.edb</TT> files are searched
directly (without loading). The particular edb file to search is
selected depending on the object name.
<P>
There are two ways of loading stars from object catalogs: Selecting
<EM>Stars/Add From Catalog</EM> will prompt for an object name and load
it. If the frame has the <TT>OBJECT</TT> FITS field set, selecting
<EM>Stars/Show Target</EM> will try to load the object specified in that
field. Stars loaded from object catalogs are of the <EM>catalog
object</EM> type.
<P>
<H2><A NAME="SECTION00522000000000000000">
Field Star Catalogs</A>
</H2>
<P>
Currently, the program supports two field star catalogs directly: GSC
(and GSC-ACT) and TYCHO2. It can also load GSC2 objects in the form of
star files (see below).
<P>
To load stars from GSC or Tycho, the frame has to have at least an
initial WCS; then select <EM>File/Load Field Stars/From GSC Catalog</EM>
or <EM>File/Load Field Stars/From Tycho2 Catalog</EM>.
<P>
Options under <EM>Star Detection and Search Options</EM> control the
maximum number of stars loaded and the limiting magnitude. When more
stars than the specified limit are found in the catalog, only the brightest
ones are loaded. The region searched is slightly larger than the
frame's size in world coordinates.
<P>
<H1><A NAME="SECTION00530000000000000000">
Star Files</A>
</H1>
<P>
<H4><A NAME="SECTION00530010000000000000">
GSC-2 files</A>
</H4> A file
containing GSC2 stars in a specified region can be obtained from
<BLOCKQUOTE>
<TT>http://www-gsss.stsci.edu/support/data_access.html</TT>
</BLOCKQUOTE>
It can be loaded into <SMALL>GCX </SMALL>by selecting <EM>File/Load Field
Stars/From GSC-2 file</EM>. Stars loaded this way are marked as
<EM>field stars</EM>.
<P>
<H4><A NAME="SECTION00530020000000000000">
Native format files</A>
</H4> <SMALL>GCX </SMALL>defines a native format for star
files. It is used for
object catalogs, photometry recipe and report files, among other
things. Stars from any of these files can be read by selecting
<EM>File/Load Recipe</EM>. The native format contains star type
information, which is maintained on loads.
<P>
<H4><A NAME="SECTION00530030000000000000">
Other star files</A>
</H4> Many star files are available from
various sources, usually in some form of tabular format. <SMALL>GCX </SMALL>has a
command-line only import function to convert these to recipe files
(see <TT>gcx -help</TT> for more details). While it can read a limited
range of formats, it is relativey easy to either convert a given file
to a supported format, or modify an existing conversion
routine.<A NAME="tex2html11"
HREF="footnode.html#foot1217"><SUP><SPAN CLASS="arabic">4</SPAN>.<SPAN CLASS="arabic">2</SPAN></SUP></A>
<P>
<H1><A NAME="SECTION00540000000000000000">
Setting up Catalogs</A>
</H1>
<P>
The program expects the various catalogs to be set up in a certain
way. Here are the requirements for the various catalogs.
<P>
<H2><A NAME="SECTION00541000000000000000">
Setting up GSC</A>
</H2>
<P>
The program reads the GSC or GSC-ACT<A NAME="tex2html12"
HREF="footnode.html#foot279"><SUP><SPAN CLASS="arabic">4</SPAN>.<SPAN CLASS="arabic">3</SPAN></SUP></A> catalogs in the compact (binary)
form. It can be downloaded in this format from:
<BLOCKQUOTE>
<TT>ftp://cdsarc.u-strasbg.fr/pub/cats/I/255/GSC_ACT/</TT>
</BLOCKQUOTE>
Place the downloaded files in a directory (for instance <TT> /usr/share/gcx/gsc-act</TT>) and set <EM>File and Device Options/GSC
Location</EM> to point to that directory. Make sure all the directory and
file names under the gsc dir use all lower case letters.
<P>
<H2><A NAME="SECTION00542000000000000000">
Setting up Tycho2</A>
</H2>
<P>
The Tycho2 catalog can be downloaded from
<BLOCKQUOTE>
<TT>ftp://cdsarc.u-strasbg.fr/pub/cats/I/259/</TT>
</BLOCKQUOTE>
We need to download all the <TT>tyc2.dat.nn.gz</TT> files, unzip
them and concatenate together to create one (big) tycho2.dat
file, perhaps like this:
<BLOCKQUOTE>
<TT>zcat tyc2.dat.??.gz >tycho2.dat</TT>
</BLOCKQUOTE>
After that, set <EM>File and Device Options/Tycho2 location</EM> to
the full path of the file, like for instance:
<BLOCKQUOTE>
<TT>/usr/share/gcx/tycho2/tycho2.dat</TT>
</BLOCKQUOTE>
<SMALL>GCX </SMALL>must have write permissions to the
directory where the <TT>tycho2.dat</TT> file is located, as it needs
to create some indexes when the catalog is first accessed.
<P>
<H2><A NAME="SECTION00543000000000000000">
Setting up Object Catalog Files</A>
</H2>
<P>
To tell the program what native format catalog files to load, set the
<EM>File and Device Options/Catalog files</EM> option to a comma-delimited
list of files. The list can contain wildcards and is
tilde-expanded. An example entry would be:
<BLOCKQUOTE>
<TT>/usr/share/gcx/catalogs/*.gcx:~/catalogs/gcvs.gcx</TT>
</BLOCKQUOTE>
<P>
All <TT>.edb</TT> files that are searched must be located in the same
directory, specified in <EM>File and Device Options/EDB
files</EM>. Depending on the searched object's name, <SMALL>GCX </SMALL>will look in a
specific file:<A NAME="tex2html13"
HREF="footnode.html#foot295"><SUP><SPAN CLASS="arabic">4</SPAN>.<SPAN CLASS="arabic">4</SPAN></SUP></A>
<P>
<P>
<BR>
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT">Objects with names starting in ``M''&<TT>Messier.edb</TT></TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">Objects with names starting in ``NGC''&<TT>NGC.edb</TT></TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">Objects with names starting in ``UGC'' or ``UGCA''&<TT>UGC.edb</TT></TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">Objects with names starting in ``IC''&<TT>IC.edb</TT></TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">Objects with names starting in ``SAO''&<TT>sao.edb</TT></TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">Objects with ending in a constellation name</TD>
<TD ALIGN="LEFT"><TT>gcvs.edb</TT></TD>
</TR>
<TR><TD ALIGN="LEFT">Other objects</TD>
<TD ALIGN="LEFT"><TT>YBS.edb</TT></TD>
</TR>
</TABLE>
<P>
<DIV CLASS="navigation"><HR>
<!--Navigation Panel-->
<A NAME="tex2html548"
HREF="node6.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
SRC="/usr/share/latex2html/icons/next.png"></A>
<A NAME="tex2html544"
HREF="gcx.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
SRC="/usr/share/latex2html/icons/up.png"></A>
<A NAME="tex2html538"
HREF="node4.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
SRC="/usr/share/latex2html/icons/prev.png"></A>
<A NAME="tex2html546"
HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
SRC="/usr/share/latex2html/icons/contents.png"></A>
<BR>
<B> Next:</B> <A NAME="tex2html549"
HREF="node6.html">World Coordinates</A>
<B> Up:</B> <A NAME="tex2html545"
HREF="gcx.html">GCX User's Manual</A>
<B> Previous:</B> <A NAME="tex2html539"
HREF="node4.html">Image Files</A>
<B> <A NAME="tex2html547"
HREF="node1.html">Contents</A></B> </DIV>
<!--End of Navigation Panel-->
<ADDRESS>
root
2005-11-27
</ADDRESS>
</BODY>
</HTML>
|
