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: PROJ4 string describing the coordinate
  59 system in use.
  60  </ul>
  61 <li> Timestamp: A string consisting of an '@' followed by a count of
  62 seconds since the start of 1970 in UTC ("Unix time_t") as a string
  63 (for example: "@1371300355"), followed by a linefeed.  This is intended to be
  64 the time the file was generated, rather than the time the survey data was
  65 collected.
  66 <li> File-wide flags: a single byte.  If bit 7 is set, this is an extended
  67 elevation.  All other bits are reserved - set them to 0 when writing, and
  68 ignore them when reading.
  69 </ul>
  70
  71 <H2>Items</H2>
  72
  73 <P>Following the header are a number of items.  The last item must be a 0x00
  74 byte when the current label is empty, which marks the end of the data.  The
  75 first byte of an item is a code identifying what the item is:</P>
  76
  77 <table border="1" cellpadding="1" cellspacing="0" width="100%">
  78 <tr>
  79     <th class="code">Code</th>
  80     <th class="code">Type</th>
  81     <th class="data">Data</th>
  82     <th class="desc" colspan="2">Meaning</th>
  83     <th class="version">Version</th>
  84 </tr>
  85 <tr>
  86     <td class="code">0x00</td>
  87     <td class="type">STYLE_NORMAL / STOP</td>
  88     <td class="data">&nbsp;</td>
  89     <td colspan="2">
  90     Set style for following legs to tape, compass and clino.
  91 <p>
  92     If the style is already set to STYLE_NORMAL, this code signifies the
  93     end of the data in the 3d file.</td>
  94     <td class="version">&ge;8</td>
  95 </tr>
  96 <tr>
  97     <td class="code">0x01</td>
  98     <td class="type">STYLE_DIVING</td>
  99     <td class="data">&nbsp;</td>
 100     <td colspan="2">
 101     Set style for following legs to diving data</td>
 102     <td class="version">&ge;8</td>
 103 </tr>
 104 <tr>
 105     <td class="code">0x02</td>
 106     <td class="type">STYLE_CARTESIAN</td>
 107     <td class="data">&nbsp;</td>
 108     <td colspan="2">
 109     Set style for following legs to cartesian data</td>
 110     <td class="version">&ge;8</td>
 111 </tr>
 112 <tr>
 113     <td class="code">0x03</td>
 114     <td class="type">STYLE_CYLPOLAR</td>
 115     <td class="data">&nbsp;</td>
 116     <td colspan="2">
 117     Set style for following legs to cylindrical polar data</td>
 118     <td class="version">&ge;8</td>
 119 </tr>
 120 <tr>
 121     <td class="code">0x04</td>
 122     <td class="type">STYLE_NOSURVEY</td>
 123     <td class="data">&nbsp;</td>
 124     <td colspan="2">
 125     Set style for following legs to unsurveyed</td>
 126     <td class="version">&ge;8</td>
 127 </tr>
 128 <tr class="reserved">
 129     <td class="code">0x05 - 0x0e</td>
 130     <td class="type">&nbsp;</td>
 131     <td class="data">&nbsp;</td>
 132     <td class="desc" colspan="3">Reserved</td>
 133 </tr>
 134 <tr>
 135     <td class="code">0x0f</td>
 136     <td class="type">MOVE</td>
 137     <td class="data">&lt;x&gt; &lt;y&gt; &lt;z&gt;</td>
 138     <td class="desc" colspan="2">
 139     Set current position to the coordinates given. Coordinates
 140     are 4 byte little-endian signed integers representing
 141     values in centimetres (0.01 metres).</td>
 142     <td class="version">&ge;8</td>
 143 </tr>
 144 <tr>
 145     <td class="code">0x10</td>
 146     <td class="type">DATE</td>
 147     <td class="data">&nbsp;</td>
 148     <td colspan="2">
 149     No survey date information was specified.</td>
 150     <td class="version">&ge;8</td>
 151 </tr>
 152 <tr>
 153     <td class="code">0x11</td>
 154     <td class="type">DATE</td>
 155     <td class="data">&lt;date&gt;</td>
 156     <td colspan="2">
 157     Set survey date of legs: date is a 2 byte little-endian unsigned integer
 158     counting days from the start of 1900.</td>
 159     <td class="version">&ge;8</td>
 160 </tr>
 161 <tr>
 162     <td class="code">0x12</td>
 163     <td class="type">DATE</td>
 164     <td class="data">&lt;date1&gt;&lt;datespan&gt;</td>
 165     <td colspan="2">
 166     Set survey date of legs to a range: date1 is a
 167     2 byte little-endian unsigned integer counting days since the start of
 168     1900, and datespan is an unsigned byte counting days from date1.</td>
 169     <td class="version">&ge;8</td>
 170 </tr>
 171 <tr>
 172     <td class="code">0x13</td>
 173     <td class="type">DATE</td>
 174     <td class="data">&lt;date1&gt;&lt;date2&gt;</td>
 175     <td colspan="2">
 176     Set survey date of legs to a range: date1, date2 are
 177     2 byte little-endian unsigned integers counting days since the
 178     start of 1900.</td>
 179     <td class="version">&ge;8</td>
 180 </tr>
 181 <tr class="reserved">
 182     <td class="code">0x14 - 0x1e</td>
 183     <td class="type">&nbsp;</td>
 184     <td class="data">&nbsp;</td>
 185     <td colspan="3">Reserved</td>
 186 </tr>
 187 <tr>
 188     <td class="code">0x1f</td>
 189     <td class="type">ERROR</td>
 190     <td class="data">&lt;legs&gt;&lt;length&gt;&lt;E&gt;&lt;H&gt;&lt;V&gt;</td>
 191     <td colspan="2">
 192     Error information for the current traverse.  &lt;legs&gt; is the number of
 193     legs. &lt;length&gt; is the total length of the
 194     traverse in cm (0.01m). E, H and V are the error and the horizontal and
 195     vertical components in cm. (All values are 4 byte little-endian signed integers) </td>
 196     <td class="version">&ge;8</td>
 197 </tr>
 198 <tr class="reserved">
 199     <td class="code">0x20 - 0x2f</td>
 200     <td class="type">&nbsp;</td>
 201     <td class="data">&nbsp;</td>
 202     <td colspan="3">Reserved</td>
 203 </tr>
 204 <tr>
 205     <td class="code" rowspan="3">0x30 - 0x31</td>
 206     <td class="type" rowspan="3">XSECT</td>
 207     <td class="data" rowspan="3">&lt;label&gt; &lt;L&gt; &lt;R&gt; &lt;U&gt; &lt;D&gt;</td>
 208     <td colspan="2">
 209     Modify the current label buffer according to &lt;label&gt; (see below for
 210     details). The updated contents of the label buffer give the full name of
 211     the survey station which these dimensions were measured at.  Dimensions are
 212     2 byte little-endian signed integers representing values in centimetres
 213     (0.01 metres). Omitted dimensions are encoded as 0xffff.  Station flags are
 214     (N &amp; 0x01):
 215     </td>
 216     <td class="version" rowspan="3">&ge;8</td>
 217 </tr>
 218 <tr>
 219     <th>Flag (N &amp; 0x01)</th>
 220     <th>Meaning</th>
 221 </tr>
 222 <tr>
 223     <td>0x01</td>
 224     <td>Station is last one in this passage</td>
 225 </tr>
 226 <tr>
 227     <td class="code" rowspan="3">0x32 - 0x33</td>
 228     <td class="type" rowspan="3">XSECT</td>
 229     <td class="data" rowspan="3">&lt;label&gt; &lt;L&gt; &lt;R&gt; &lt;U&gt; &lt;D&gt;</td>
 230     <td colspan="2">
 231     Modify the current label buffer according to &lt;label&gt; (see below for
 232     details). The updated contents of the label buffer give the full name of
 233     the survey station which these dimensions were measured at.  Dimensions are
 234     4 byte little-endian signed integers representing values in centimetres
 235     (0.01 metres). Omitted dimensions are encoded as 0xffffffff.
 236     </td>
 237     <td class="version" rowspan="3">&ge;8</td>
 238 </tr>
 239 <tr>
 240     <th>Flag (N &amp; 0x01)</th>
 241     <th>Meaning</th>
 242 </tr>
 243 <tr>
 244     <td>0x01</td>
 245     <td>Station is last one in this passage</td>
 246 </tr>
 247 <tr class="reserved">
 248     <td class="code">0x34 - 0x3f</td>
 249     <td class="type">&nbsp;</td>
 250     <td class="data">&nbsp;</td>
 251     <td colspan="3">Reserved</td>
 252 </tr>
 253 <!-- Checked to here! -->
 254 <tr>
 255     <td class="code" rowspan="8">0x40 - 0x7f</td>
 256     <td class="type" rowspan="8">LINE</td>
 257     <td class="data" rowspan="8">&lt;label&gt; &lt;x&gt; &lt;y&gt; &lt;z&gt;</td>
 258     <td colspan="2">
 259     Modify the current label buffer according to &lt;label&gt; (see below for
 260     details) - if &lt;label&gt; is omitted due to flag bit 0x20 being set then
 261     the current label buffer is used unmodified. The updated contents of the
 262     label buffer give the survey that the leg is in. Return leg from current
 263     position to coordinates given, and update current position to coordinates
 264     given.
 265     </td>
 266     <td class="version" rowspan="5">&ge;8</td>
 267 </tr>
 268 <tr>
 269     <th>Flag (N &amp; 0x3f)</th>
 270     <th>Meaning</th>
 271 </tr>
 272 <tr>
 273     <td>0x01</td>
 274     <td>Leg is above ground</td>
 275 </tr>
 276 <tr>
 277     <td>0x02</td>
 278     <td>Leg duplicates data in another leg (e.g. resurvey along a passage to
 279     tie into a known station)</td>
 280 </tr>
 281 <tr>
 282     <td>0x04</td>
 283     <td>Leg is a splay shot in a chamber (radial shots from a central point)</td>
 284 </tr>
 285 <tr class="reserved">
 286     <td>0x08</td>
 287     <td colspan="2">Reserved</td>
 288 </tr>
 289 <tr class="reserved">
 290     <td>0x10</td>
 291     <td colspan="2">Reserved</td>
 292 </tr>
 293 <tr>
 294     <td>0x20</td>
 295     <td>No change to label (&lt;label&gt; omitted entirely)</td>
 296     <td class="version">&ge;8</td>
 297 </tr>
 298 <tr>
 299     <td class="code" rowspan="10">0x80 - 0xff</td>
 300     <td class="type" rowspan="10">LABEL</td>
 301     <td class="data" rowspan="10">&lt;label&gt; &lt;x&gt; &lt;y&gt; &lt;z&gt;</td>
 302     <td colspan="2">
 303     Modify the current label buffer according to &lt;label&gt; (see below for
 304     details). The updated contents of the label buffer give the survey
 305     station's full name.
 306     </td>
 307     <td class="version" rowspan="10">&ge;8</td>
 308 </tr>
 309 <tr>
 310     <td colspan="2">
 311     The station flags are encoded in the bottom 7 bits of the item code:</td>
 312 </tr>
 313 <tr>
 314     <th>Flag (N &amp; 0x7f)</th>
 315     <th>Meaning</th>
 316 </tr>
 317 <tr>
 318     <td>0x01</td>
 319     <td>Station is on leg above ground</td>
 320 </tr>
 321 <tr>
 322     <td>0x02</td>
 323     <td>Station is on an underground leg (both may be true at an entrance)</td>
 324 </tr>
 325 <tr>
 326     <td>0x04</td>
 327     <td>Station is marked as an entrance (with *entrance)</td>
 328 </tr>
 329 <tr>
 330     <td>0x08</td>
 331     <td>Station is exported (i.e. may be used as a connection point to other
 332     surveys)</td>
 333 </tr>
 334 <tr>
 335     <td>0x10</td>
 336     <td>Station is a fixed point (control point)</td>
 337 </tr>
 338 <tr>
 339     <td>0x20</td>
 340     <td>Station is anonymous</td>
 341 </tr>
 342 <tr>
 343     <td>0x40</td>
 344     <td>Station is on the passage wall</td>
 345 </tr>
 346 </table>
 347
 348 <p>A &lt;label&gt; value in the tabel above encodes modifications to the
 349 current label buffer, which consist of removing the last <i>D</i> bytes
 350 from the buffer, and then appending the next <i>A</i> bytes from the file
 351 to the buffer.  <i>D</i> and <i>A</i> are encoded as follows:</p>
 352
 353 <ul>
 354 <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>
 355 <li>Otherwise (i.e. the first byte is zero):
 356   <ul>
 357   <li>Read a byte and:
 358     <ul>
 359     <li>If it is not 255 then <i>D</i> = <code>byte</code>
 360     <li>Otherwise, <i>D</i> = 4 byte unsigned integer read from the file
 361     </ul>
 362   <li>Read a byte and:
 363     <ul>
 364     <li>If it is not 255 then <i>A</i> = <code>byte</code>
 365     <li>Otherwise, <i>A</i> = 4 byte unsigned integer read from the file
 366     </ul>
 367   </ul>
 368 </ul>
 369
 370 <H2>Item order</H2>
 371 <ul>
 372 <li>A continuous section of centreline is defined by a &lt;MOVE&gt; item, followed
 373 by one or more &lt;LINE&gt; items.</li>
 374 <li>&lt;LABEL&gt; items may appear anywhere in the file after the header,
 375 including within a &lt;MOVE&gt;&lt;LINE&gt;... sequence.</li>
 376 <li>Duplicate &lt;LABEL&gt; items are permitted provided they also have identical
 377 coordinate values. (The same coordinate values may also be shared by any
 378 number of different &lt;LABEL&gt; items).</li>
 379 <li>Stations must be defined in a &lt;LABEL&gt; item <u>before</u> being
 380 referenced (e.g. in &lt;XSECT&gt; items)</li>
 381 </ul>
 382
 383 <P>Authors: Olly Betts and Mike McCombe, last updated: 2016-05-17</P>
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