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<!DOCTYPE HTML PUBLIC "-//W4C//DTD HTML 4.0 Transitional//EN">
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<TITLE>Survex 3d Format Specification</TITLE>
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<H1>Survex 3d Format Specification</H1>
<P>If you're writing in C or C++ it's <b>strongly</b> recommended
that you use the img routine provided with Survex to read and write
3d files. Doing so means that you can take advantage of any revisions
to the 3d format by simply rebuilding your software with the updated
img routines, rather than having to update your own code. It also
allows you to read other processed survey data formats (those from
Larry Fish's Compass and from Bob Thrun's CMAP), and allows reading
a sub-set of the data in a file, restricted by survey prefix.</P>
<P>This document only describes the most recent revision of the 3d format
(version 8) which is produced by versions from 1.2.7. A <a
href="3dformat-old.htm">separate document</a> describes older versions.
</P>
<P>If you try to use this specification and find details which aren't
spelled out clearly enough (or at all!) or any errors, please let us know.
At least two people have successfully written code to read 3d files
using this document, but that doesn't mean it can't be improved.
</P>
<H2>File Header</H2>
<P>This consists of:</P>
<ul>
<li> File ID: the string "Survex 3D Image File" followed by a linefeed
(decimal 10, hex 0a). [Note: v0.01 files can have a carriage return
before this and other linefeeds - this is a file format error in any
other format version].
<li> File format version: "v8" followed by a linefeed.
Any future versions will be "v9", "v10", "v11", etc.
<li> Assorted string metadata - the sublist below lists these, and they
must appear in the order given, separated by zero bytes, with the end of
the metadata marked by a linefeed. More items may be added, so ignore any
additional ones which are present. Any trailing items with empty values
can be omitted along with the separating zero byte before them.
<ul>
<li>Survey title: Human readable description of the data in the file.
There's no length limit on this string.
<li>Coordinate system: string describing the coordinate system in use
which can be passed to PROJ. For a coordinate system with an EPSG code
<code>EPSG:</code> followed by the code number can be used (we recommend
using this if an EPSG code exists). Similarly, an ESRI code can be specified
with <code>ESRI:</code> followed by the code number.
<li>Survey hierarchy separator character. Survey station names form a
hierarchy, and this character separates levels in the hierarchy. E.g.
<code>161.entrance.6</code>. Defaults to <code>.</code> if this item is not
specified, which is also the recommended character to use unless <code>.</code>
is used in survey or station names (especially as older software will not see
this metadata and will use <code>.</code> unconditionally).
</ul>
<li> Timestamp: A string consisting of an '@' followed by a count of
seconds since the start of 1970 in UTC ("Unix time_t") as a string
(for example: "@1371300355"), followed by a linefeed. This is intended to be
the time the file was generated, rather than the time the survey data was
collected.
<li> File-wide flags: a single byte. If bit 7 is set, this is an extended
elevation. All other bits are reserved - set them to 0 when writing, and
ignore them when reading.
</ul>
<H2>Items</H2>
<P>Following the header are a number of items. The last item must be a 0x00
byte when the current label is empty, which marks the end of the data. The
first byte of an item is a code identifying what the item is:</P>
<table border="1" cellpadding="1" cellspacing="0" width="100%">
<tr>
<th class="code">Code</th>
<th class="code">Type</th>
<th class="data">Data</th>
<th class="desc" colspan="2">Meaning</th>
<th class="version">Version</th>
</tr>
<tr>
<td class="code">0x00</td>
<td class="type">STYLE_NORMAL / STOP</td>
<td class="data"> </td>
<td colspan="2">
Set style for following legs to tape, compass and clino.
<p>
If the style is already set to STYLE_NORMAL, this code signifies the
end of the data in the 3d file.</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x01</td>
<td class="type">STYLE_DIVING</td>
<td class="data"> </td>
<td colspan="2">
Set style for following legs to diving data</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x02</td>
<td class="type">STYLE_CARTESIAN</td>
<td class="data"> </td>
<td colspan="2">
Set style for following legs to cartesian data</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x03</td>
<td class="type">STYLE_CYLPOLAR</td>
<td class="data"> </td>
<td colspan="2">
Set style for following legs to cylindrical polar data</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x04</td>
<td class="type">STYLE_NOSURVEY</td>
<td class="data"> </td>
<td colspan="2">
Set style for following legs to unsurveyed</td>
<td class="version">≥8</td>
</tr>
<tr class="reserved">
<td class="code">0x05 - 0x0e</td>
<td class="type"> </td>
<td class="data"> </td>
<td class="desc" colspan="3">Reserved</td>
</tr>
<tr>
<td class="code">0x0f</td>
<td class="type">MOVE</td>
<td class="data"><x> <y> <z></td>
<td class="desc" colspan="2">
Set current position to the coordinates given. Coordinates
are 4 byte little-endian signed integers representing
values in centimetres (0.01 metres).</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x10</td>
<td class="type">DATE</td>
<td class="data"> </td>
<td colspan="2">
No survey date information was specified.</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x11</td>
<td class="type">DATE</td>
<td class="data"><date></td>
<td colspan="2">
Set survey date of legs: date is a 2 byte little-endian unsigned integer
counting days from the start of 1900.</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x12</td>
<td class="type">DATE</td>
<td class="data"><date1><datespan></td>
<td colspan="2">
Set survey date of legs to a range: date1 is a
2 byte little-endian unsigned integer counting days since the start of
1900, and datespan is an unsigned byte counting days from date1.</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code">0x13</td>
<td class="type">DATE</td>
<td class="data"><date1><date2></td>
<td colspan="2">
Set survey date of legs to a range: date1, date2 are
2 byte little-endian unsigned integers counting days since the
start of 1900.</td>
<td class="version">≥8</td>
</tr>
<tr class="reserved">
<td class="code">0x14 - 0x1e</td>
<td class="type"> </td>
<td class="data"> </td>
<td colspan="3">Reserved</td>
</tr>
<tr>
<td class="code">0x1f</td>
<td class="type">ERROR</td>
<td class="data"><legs><length><E><H><V></td>
<td colspan="2">
Error information for the current traverse. <legs> is the number of
legs. <length> is the total length of the
traverse in cm (0.01m). E, H and V are the error and the horizontal and
vertical components in cm. (All values are 4 byte little-endian signed integers) </td>
<td class="version">≥8</td>
</tr>
<tr class="reserved">
<td class="code">0x20 - 0x2f</td>
<td class="type"> </td>
<td class="data"> </td>
<td colspan="3">Reserved</td>
</tr>
<tr>
<td class="code" rowspan="3">0x30 - 0x31</td>
<td class="type" rowspan="3">XSECT</td>
<td class="data" rowspan="3"><label> <L> <R> <U> <D></td>
<td colspan="2">
Modify the current label buffer according to <label> (see below for
details). The updated contents of the label buffer give the full name of
the survey station which these dimensions were measured at. Dimensions are
2 byte little-endian signed integers representing values in centimetres
(0.01 metres). Omitted dimensions are encoded as 0xffff. Station flags are
(N & 0x01):
</td>
<td class="version" rowspan="3">≥8</td>
</tr>
<tr>
<th>Flag (N & 0x01)</th>
<th>Meaning</th>
</tr>
<tr>
<td>0x01</td>
<td>Station is last one in this passage</td>
</tr>
<tr>
<td class="code" rowspan="3">0x32 - 0x33</td>
<td class="type" rowspan="3">XSECT</td>
<td class="data" rowspan="3"><label> <L> <R> <U> <D></td>
<td colspan="2">
Modify the current label buffer according to <label> (see below for
details). The updated contents of the label buffer give the full name of
the survey station which these dimensions were measured at. Dimensions are
4 byte little-endian signed integers representing values in centimetres
(0.01 metres). Omitted dimensions are encoded as 0xffffffff.
</td>
<td class="version" rowspan="3">≥8</td>
</tr>
<tr>
<th>Flag (N & 0x01)</th>
<th>Meaning</th>
</tr>
<tr>
<td>0x01</td>
<td>Station is last one in this passage</td>
</tr>
<tr class="reserved">
<td class="code">0x34 - 0x3f</td>
<td class="type"> </td>
<td class="data"> </td>
<td colspan="3">Reserved</td>
</tr>
<!-- Checked to here! -->
<tr>
<td class="code" rowspan="8">0x40 - 0x7f</td>
<td class="type" rowspan="8">LINE</td>
<td class="data" rowspan="8"><label> <x> <y> <z></td>
<td colspan="2">
Modify the current label buffer according to <label> (see below for
details) - if <label> is omitted due to flag bit 0x20 being set then
the current label buffer is used unmodified. The updated contents of the
label buffer give the survey that the leg is in. Return leg from current
position to coordinates given, and update current position to coordinates
given.
</td>
<td class="version" rowspan="5">≥8</td>
</tr>
<tr>
<th>Flag (N & 0x3f)</th>
<th>Meaning</th>
</tr>
<tr>
<td>0x01</td>
<td>Leg is above ground</td>
</tr>
<tr>
<td>0x02</td>
<td>Leg duplicates data in another leg (e.g. resurvey along a passage to
tie into a known station)</td>
</tr>
<tr>
<td>0x04</td>
<td>Leg is a splay shot in a chamber (radial shots from a central point)</td>
</tr>
<tr class="reserved">
<td>0x08</td>
<td colspan="2">Reserved</td>
</tr>
<tr class="reserved">
<td>0x10</td>
<td colspan="2">Reserved</td>
</tr>
<tr>
<td>0x20</td>
<td>No change to label (<label> omitted entirely)</td>
<td class="version">≥8</td>
</tr>
<tr>
<td class="code" rowspan="10">0x80 - 0xff</td>
<td class="type" rowspan="10">LABEL</td>
<td class="data" rowspan="10"><label> <x> <y> <z></td>
<td colspan="2">
Modify the current label buffer according to <label> (see below for
details). The updated contents of the label buffer give the survey
station's full name.
</td>
<td class="version" rowspan="10">≥8</td>
</tr>
<tr>
<td colspan="2">
The station flags are encoded in the bottom 7 bits of the item code:</td>
</tr>
<tr>
<th>Flag (N & 0x7f)</th>
<th>Meaning</th>
</tr>
<tr>
<td>0x01</td>
<td>Station is on leg above ground</td>
</tr>
<tr>
<td>0x02</td>
<td>Station is on an underground leg (both may be true at an entrance)</td>
</tr>
<tr>
<td>0x04</td>
<td>Station is marked as an entrance (with *entrance)</td>
</tr>
<tr>
<td>0x08</td>
<td>Station is exported (i.e. may be used as a connection point to other
surveys)</td>
</tr>
<tr>
<td>0x10</td>
<td>Station is a fixed point (control point)</td>
</tr>
<tr>
<td>0x20</td>
<td>Station is anonymous</td>
</tr>
<tr>
<td>0x40</td>
<td>Station is on the passage wall</td>
</tr>
</table>
<p>A <label> value in the table above encodes modifications to the
current label buffer, which consist of removing the last <i>D</i> bytes
from the buffer, and then appending the next <i>A</i> bytes from the file
to the buffer. <i>D</i> and <i>A</i> are encoded as follows:</p>
<ul>
<li>Read a byte - if it is non-zero then: <i>D</i> = <code>byte >> 4</code>, <i>A</i> = <code>byte & 0x0f</code>
<li>Otherwise (i.e. the first byte is zero):
<ul>
<li>Read a byte and:
<ul>
<li>If it is not 255 then <i>D</i> = <code>byte</code>
<li>Otherwise, <i>D</i> = 4 byte unsigned integer read from the file
</ul>
<li>Read a byte and:
<ul>
<li>If it is not 255 then <i>A</i> = <code>byte</code>
<li>Otherwise, <i>A</i> = 4 byte unsigned integer read from the file
</ul>
</ul>
</ul>
<H2>Item order</H2>
<ul>
<li>A continuous section of centreline is defined by a <MOVE> item, followed
by one or more <LINE> items.</li>
<li><LABEL> items may appear anywhere in the file after the header,
including within a <MOVE><LINE>... sequence.</li>
<li>Duplicate <LABEL> items are permitted provided they also have identical
coordinate values. (The same coordinate values may also be shared by any
number of different <LABEL> items).</li>
<li>Stations must be defined in a <LABEL> item <u>before</u> being
referenced (e.g. in <XSECT> items)</li>
</ul>
<P>Authors: Olly Betts and Mike McCombe, last updated: 2025-01-13</P>
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