doc/3dformat.htm

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   3 <TITLE>Survex 3d Format Specification</TITLE>
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  18 <H1>Survex 3d Format Specification</H1>
  19
  20 <P>If you're writing in C or C++ it's <b>strongly</b> recommended
  21 that you use the img routine provided with Survex to read and write
  22 3d files.  Doing so means that you can take advantage of any revisions
  23 to the 3d format by simply rebuilding your software with the updated
  24 img routines, rather than having to update your own code.  It also
  25 allows you to read a sub-set of the data in the file, restricted by
  26 Survey prefix.</P>
  27
  28 <P>This document only describes the most recent revision of the 3d format
  29 (version 8) which is produced by versions from 1.2.7.  A <a
  30 href="3dformat-old.htm">separate document</a> describes older versions.
  31 </P>
  32
  33 <P>If you try to use this specification and find details which aren't
  34 spelled out clearly enough (or at all!) or any errors, please let us know.
  35 At least two people have successfully written code to read 3d files
  36 using this document, but that doesn't mean it can't be improved.
  37 </P>
  38
  39 <H2>File Header</H2>
  40
  41 <P>This consists of:</P>
  42
  43 <ul>
  44 <li> File ID: the string "Survex 3D Image File" followed by a linefeed
  45 (decimal 10, hex 0a). [Note: v0.01 files can have a carriage return
  46 before this and other linefeeds - this is a file format error in any
  47 other format version].
  48 <li> File format version: "v8" followed by a linefeed.
  49 Any future versions will be "v9", "v10", "v11", etc.
  50 <li> Assorted string metadata - the sublist below lists these, and they
  51 must appear in the order given, separated by zero bytes, with the end of
  52 the metadata marked by a linefeed.  More items may be added, so ignore any
  53 additional ones which are present.  Any trailing items with empty values
  54 can be omitted along with the separating zero byte before them.
  55  <ul>
  56   <li>Survey title: Human readable description of the data in the file.
  57 There's no length limit on this string.
  58   <li>Coordinate system: string describing the coordinate system in use
  59 which can be passed to PROJ.  For a coordinate system with an EPSG code
  60 <code>EPSG:</code> followed by the code number can be used (we recommend
  61 using this if an EPSG code exists).  Similarly, an ESRI code can be specified
  62 with <code>ESRI:</code> followed by the code number.
  63   <li>Survey hierarchy separator character.  Survey station names form a
  64 hierarchy, and this character separates levels in the hierarchy.  E.g.
  65 <code>161.entrance.6</code>.  Defaults to <code>.</code> if this item is not
  66 specified, which is also the recommended character to use unless <code>.</code>
  67 is used in survey or station names (especially as older software will not see
  68 this metadata and will use <code>.</code> unconditionally).
  69  </ul>
  70 <li> Timestamp: A string consisting of an '@' followed by a count of
  71 seconds since the start of 1970 in UTC ("Unix time_t") as a string
  72 (for example: "@1371300355"), followed by a linefeed.  This is intended to be
  73 the time the file was generated, rather than the time the survey data was
  74 collected.
  75 <li> File-wide flags: a single byte.  If bit 7 is set, this is an extended
  76 elevation.  All other bits are reserved - set them to 0 when writing, and
  77 ignore them when reading.
  78 </ul>
  79
  80 <H2>Items</H2>
  81
  82 <P>Following the header are a number of items.  The last item must be a 0x00
  83 byte when the current label is empty, which marks the end of the data.  The
  84 first byte of an item is a code identifying what the item is:</P>
  85
  86 <table border="1" cellpadding="1" cellspacing="0" width="100%">
  87 <tr>
  88     <th class="code">Code</th>
  89     <th class="code">Type</th>
  90     <th class="data">Data</th>
  91     <th class="desc" colspan="2">Meaning</th>
  92     <th class="version">Version</th>
  93 </tr>
  94 <tr>
  95     <td class="code">0x00</td>
  96     <td class="type">STYLE_NORMAL / STOP</td>
  97     <td class="data">&nbsp;</td>
  98     <td colspan="2">
  99     Set style for following legs to tape, compass and clino.
 100 <p>
 101     If the style is already set to STYLE_NORMAL, this code signifies the
 102     end of the data in the 3d file.</td>
 103     <td class="version">&ge;8</td>
 104 </tr>
 105 <tr>
 106     <td class="code">0x01</td>
 107     <td class="type">STYLE_DIVING</td>
 108     <td class="data">&nbsp;</td>
 109     <td colspan="2">
 110     Set style for following legs to diving data</td>
 111     <td class="version">&ge;8</td>
 112 </tr>
 113 <tr>
 114     <td class="code">0x02</td>
 115     <td class="type">STYLE_CARTESIAN</td>
 116     <td class="data">&nbsp;</td>
 117     <td colspan="2">
 118     Set style for following legs to cartesian data</td>
 119     <td class="version">&ge;8</td>
 120 </tr>
 121 <tr>
 122     <td class="code">0x03</td>
 123     <td class="type">STYLE_CYLPOLAR</td>
 124     <td class="data">&nbsp;</td>
 125     <td colspan="2">
 126     Set style for following legs to cylindrical polar data</td>
 127     <td class="version">&ge;8</td>
 128 </tr>
 129 <tr>
 130     <td class="code">0x04</td>
 131     <td class="type">STYLE_NOSURVEY</td>
 132     <td class="data">&nbsp;</td>
 133     <td colspan="2">
 134     Set style for following legs to unsurveyed</td>
 135     <td class="version">&ge;8</td>
 136 </tr>
 137 <tr class="reserved">
 138     <td class="code">0x05 - 0x0e</td>
 139     <td class="type">&nbsp;</td>
 140     <td class="data">&nbsp;</td>
 141     <td class="desc" colspan="3">Reserved</td>
 142 </tr>
 143 <tr>
 144     <td class="code">0x0f</td>
 145     <td class="type">MOVE</td>
 146     <td class="data">&lt;x&gt; &lt;y&gt; &lt;z&gt;</td>
 147     <td class="desc" colspan="2">
 148     Set current position to the coordinates given. Coordinates
 149     are 4 byte little-endian signed integers representing
 150     values in centimetres (0.01 metres).</td>
 151     <td class="version">&ge;8</td>
 152 </tr>
 153 <tr>
 154     <td class="code">0x10</td>
 155     <td class="type">DATE</td>
 156     <td class="data">&nbsp;</td>
 157     <td colspan="2">
 158     No survey date information was specified.</td>
 159     <td class="version">&ge;8</td>
 160 </tr>
 161 <tr>
 162     <td class="code">0x11</td>
 163     <td class="type">DATE</td>
 164     <td class="data">&lt;date&gt;</td>
 165     <td colspan="2">
 166     Set survey date of legs: date is a 2 byte little-endian unsigned integer
 167     counting days from the start of 1900.</td>
 168     <td class="version">&ge;8</td>
 169 </tr>
 170 <tr>
 171     <td class="code">0x12</td>
 172     <td class="type">DATE</td>
 173     <td class="data">&lt;date1&gt;&lt;datespan&gt;</td>
 174     <td colspan="2">
 175     Set survey date of legs to a range: date1 is a
 176     2 byte little-endian unsigned integer counting days since the start of
 177     1900, and datespan is an unsigned byte counting days from date1.</td>
 178     <td class="version">&ge;8</td>
 179 </tr>
 180 <tr>
 181     <td class="code">0x13</td>
 182     <td class="type">DATE</td>
 183     <td class="data">&lt;date1&gt;&lt;date2&gt;</td>
 184     <td colspan="2">
 185     Set survey date of legs to a range: date1, date2 are
 186     2 byte little-endian unsigned integers counting days since the
 187     start of 1900.</td>
 188     <td class="version">&ge;8</td>
 189 </tr>
 190 <tr class="reserved">
 191     <td class="code">0x14 - 0x1e</td>
 192     <td class="type">&nbsp;</td>
 193     <td class="data">&nbsp;</td>
 194     <td colspan="3">Reserved</td>
 195 </tr>
 196 <tr>
 197     <td class="code">0x1f</td>
 198     <td class="type">ERROR</td>
 199     <td class="data">&lt;legs&gt;&lt;length&gt;&lt;E&gt;&lt;H&gt;&lt;V&gt;</td>
 200     <td colspan="2">
 201     Error information for the current traverse.  &lt;legs&gt; is the number of
 202     legs. &lt;length&gt; is the total length of the
 203     traverse in cm (0.01m). E, H and V are the error and the horizontal and
 204     vertical components in cm. (All values are 4 byte little-endian signed integers) </td>
 205     <td class="version">&ge;8</td>
 206 </tr>
 207 <tr class="reserved">
 208     <td class="code">0x20 - 0x2f</td>
 209     <td class="type">&nbsp;</td>
 210     <td class="data">&nbsp;</td>
 211     <td colspan="3">Reserved</td>
 212 </tr>
 213 <tr>
 214     <td class="code" rowspan="3">0x30 - 0x31</td>
 215     <td class="type" rowspan="3">XSECT</td>
 216     <td class="data" rowspan="3">&lt;label&gt; &lt;L&gt; &lt;R&gt; &lt;U&gt; &lt;D&gt;</td>
 217     <td colspan="2">
 218     Modify the current label buffer according to &lt;label&gt; (see below for
 219     details). The updated contents of the label buffer give the full name of
 220     the survey station which these dimensions were measured at.  Dimensions are
 221     2 byte little-endian signed integers representing values in centimetres
 222     (0.01 metres). Omitted dimensions are encoded as 0xffff.  Station flags are
 223     (N &amp; 0x01):
 224     </td>
 225     <td class="version" rowspan="3">&ge;8</td>
 226 </tr>
 227 <tr>
 228     <th>Flag (N &amp; 0x01)</th>
 229     <th>Meaning</th>
 230 </tr>
 231 <tr>
 232     <td>0x01</td>
 233     <td>Station is last one in this passage</td>
 234 </tr>
 235 <tr>
 236     <td class="code" rowspan="3">0x32 - 0x33</td>
 237     <td class="type" rowspan="3">XSECT</td>
 238     <td class="data" rowspan="3">&lt;label&gt; &lt;L&gt; &lt;R&gt; &lt;U&gt; &lt;D&gt;</td>
 239     <td colspan="2">
 240     Modify the current label buffer according to &lt;label&gt; (see below for
 241     details). The updated contents of the label buffer give the full name of
 242     the survey station which these dimensions were measured at.  Dimensions are
 243     4 byte little-endian signed integers representing values in centimetres
 244     (0.01 metres). Omitted dimensions are encoded as 0xffffffff.
 245     </td>
 246     <td class="version" rowspan="3">&ge;8</td>
 247 </tr>
 248 <tr>
 249     <th>Flag (N &amp; 0x01)</th>
 250     <th>Meaning</th>
 251 </tr>
 252 <tr>
 253     <td>0x01</td>
 254     <td>Station is last one in this passage</td>
 255 </tr>
 256 <tr class="reserved">
 257     <td class="code">0x34 - 0x3f</td>
 258     <td class="type">&nbsp;</td>
 259     <td class="data">&nbsp;</td>
 260     <td colspan="3">Reserved</td>
 261 </tr>
 262 <!-- Checked to here! -->
 263 <tr>
 264     <td class="code" rowspan="8">0x40 - 0x7f</td>
 265     <td class="type" rowspan="8">LINE</td>
 266     <td class="data" rowspan="8">&lt;label&gt; &lt;x&gt; &lt;y&gt; &lt;z&gt;</td>
 267     <td colspan="2">
 268     Modify the current label buffer according to &lt;label&gt; (see below for
 269     details) - if &lt;label&gt; is omitted due to flag bit 0x20 being set then
 270     the current label buffer is used unmodified. The updated contents of the
 271     label buffer give the survey that the leg is in. Return leg from current
 272     position to coordinates given, and update current position to coordinates
 273     given.
 274     </td>
 275     <td class="version" rowspan="5">&ge;8</td>
 276 </tr>
 277 <tr>
 278     <th>Flag (N &amp; 0x3f)</th>
 279     <th>Meaning</th>
 280 </tr>
 281 <tr>
 282     <td>0x01</td>
 283     <td>Leg is above ground</td>
 284 </tr>
 285 <tr>
 286     <td>0x02</td>
 287     <td>Leg duplicates data in another leg (e.g. resurvey along a passage to
 288     tie into a known station)</td>
 289 </tr>
 290 <tr>
 291     <td>0x04</td>
 292     <td>Leg is a splay shot in a chamber (radial shots from a central point)</td>
 293 </tr>
 294 <tr class="reserved">
 295     <td>0x08</td>
 296     <td colspan="2">Reserved</td>
 297 </tr>
 298 <tr class="reserved">
 299     <td>0x10</td>
 300     <td colspan="2">Reserved</td>
 301 </tr>
 302 <tr>
 303     <td>0x20</td>
 304     <td>No change to label (&lt;label&gt; omitted entirely)</td>
 305     <td class="version">&ge;8</td>
 306 </tr>
 307 <tr>
 308     <td class="code" rowspan="10">0x80 - 0xff</td>
 309     <td class="type" rowspan="10">LABEL</td>
 310     <td class="data" rowspan="10">&lt;label&gt; &lt;x&gt; &lt;y&gt; &lt;z&gt;</td>
 311     <td colspan="2">
 312     Modify the current label buffer according to &lt;label&gt; (see below for
 313     details). The updated contents of the label buffer give the survey
 314     station's full name.
 315     </td>
 316     <td class="version" rowspan="10">&ge;8</td>
 317 </tr>
 318 <tr>
 319     <td colspan="2">
 320     The station flags are encoded in the bottom 7 bits of the item code:</td>
 321 </tr>
 322 <tr>
 323     <th>Flag (N &amp; 0x7f)</th>
 324     <th>Meaning</th>
 325 </tr>
 326 <tr>
 327     <td>0x01</td>
 328     <td>Station is on leg above ground</td>
 329 </tr>
 330 <tr>
 331     <td>0x02</td>
 332     <td>Station is on an underground leg (both may be true at an entrance)</td>
 333 </tr>
 334 <tr>
 335     <td>0x04</td>
 336     <td>Station is marked as an entrance (with *entrance)</td>
 337 </tr>
 338 <tr>
 339     <td>0x08</td>
 340     <td>Station is exported (i.e. may be used as a connection point to other
 341     surveys)</td>
 342 </tr>
 343 <tr>
 344     <td>0x10</td>
 345     <td>Station is a fixed point (control point)</td>
 346 </tr>
 347 <tr>
 348     <td>0x20</td>
 349     <td>Station is anonymous</td>
 350 </tr>
 351 <tr>
 352     <td>0x40</td>
 353     <td>Station is on the passage wall</td>
 354 </tr>
 355 </table>
 356
 357 <p>A &lt;label&gt; value in the table above encodes modifications to the
 358 current label buffer, which consist of removing the last <i>D</i> bytes
 359 from the buffer, and then appending the next <i>A</i> bytes from the file
 360 to the buffer.  <i>D</i> and <i>A</i> are encoded as follows:</p>
 361
 362 <ul>
 363 <li>Read a byte - if it is non-zero then: <i>D</i> = <code>byte &gt;&gt; 4</code>, <i>A</i> = <code>byte &amp; 0x0f</code>
 364 <li>Otherwise (i.e. the first byte is zero):
 365   <ul>
 366   <li>Read a byte and:
 367     <ul>
 368     <li>If it is not 255 then <i>D</i> = <code>byte</code>
 369     <li>Otherwise, <i>D</i> = 4 byte unsigned integer read from the file
 370     </ul>
 371   <li>Read a byte and:
 372     <ul>
 373     <li>If it is not 255 then <i>A</i> = <code>byte</code>
 374     <li>Otherwise, <i>A</i> = 4 byte unsigned integer read from the file
 375     </ul>
 376   </ul>
 377 </ul>
 378
 379 <H2>Item order</H2>
 380 <ul>
 381 <li>A continuous section of centreline is defined by a &lt;MOVE&gt; item, followed
 382 by one or more &lt;LINE&gt; items.</li>
 383 <li>&lt;LABEL&gt; items may appear anywhere in the file after the header,
 384 including within a &lt;MOVE&gt;&lt;LINE&gt;... sequence.</li>
 385 <li>Duplicate &lt;LABEL&gt; items are permitted provided they also have identical
 386 coordinate values. (The same coordinate values may also be shared by any
 387 number of different &lt;LABEL&gt; items).</li>
 388 <li>Stations must be defined in a &lt;LABEL&gt; item <u>before</u> being
 389 referenced (e.g. in &lt;XSECT&gt; items)</li>
 390 </ul>
 391
 392 <P>Authors: Olly Betts and Mike McCombe, last updated: 2024-03-05</P>
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