therionsurface2survex

Convert therion (or GDAL) surface meshes to survex (or therion) surface legs.

Usage: [-hsd] [-o outfile] [-i infile] -- [infile]
  -o outfile    File to write to. Will be derived from infile if not specified.  
  -i infile     File to read from, if not given by last parameter. 
  -h            Print this help and exit.
  -s            Skip check of contents - process entire file (use in case
                your therion grid data file has no "surface" declaration
  -t            Export in therion centerline format (implicit if -o ends with '.th')
  -d            debug mode: spew any action on stdout

This is a command line tool. Double clicking it on windows will do nothing. Please run cmd (windows) or your favorite shell/terminal (linux) in this case.

Example 1 (therion native): ./therionsurface2survex -t -o surface.mesh.th example/surface.th results in surface.mesh.th being generated (in therion format).

Example 2 (survex format): ./therionsurface2survex example/surface.th results in surface.th.swx being generated.

Description

The main intend of this progam is to generate survex surface meshes that will be processed by survex cavern program. This generates a 3d-file that can be merged with your cave by therion. This way you can use your existing therion digital elevation model (DEM) and include it in therions 3d-export; for example to get the distance from the cave passage to the surface.

Input formats

The supported input formats are:

• Therion source file
  Assumed is a file containing the surface/endsurface block. cs command will be parsed so the resulting .swx will be georeferenced properly.
  In case the data is not inside a surface block, you can invoke -s parameter to enable parsing of the whole file.

• GDAL ASCII grid file
  With gdal_translate -of AAIGrid ... you can convert a given heightmap from binary to ASCII, suitable to be used by therion (after adding some therion commands). The programm will recognize the GDAL header in this ASCII grid file and ceate the .swx.
  The drawback is, that the grid file does not contain any coordinate system reference, so you need to add this manually afterwards (eg. add *cs EPSG:31258 and *cs out EPSG:31258 into the resulting .swx at the start of the file).

Output formats

The supported output formats are:

• Survex (default)
  The output file is in survex .swx format, suitable to be processed from cavern to create a survex 3d-file, which contains the 3d mesh.
  Each grid section is translated to a station. Station names follow the naming scheme surface.<row>.<column>, where row and column is the cell address from the source therion file.

• Therion source file (with -t or output name ends in .th)
  The output is in therions .th centerline format, suitable to be source'd from therion thconfig files which may be even easier to combine with you cave data in therion.

How it operates

It reads the input file line by line and tries to parse any relevant therion commands (or GDAL headers), most notably cs, grid and of couse the grids data. It tries to skip lines outside of "surface" blocks and as a last resort starts parsing when detecting a "grid" command.

In case you separate the grid data from the surrounding therion commands (like surface, bitmap, cs and so on), you can use the -s option to disable the checks alltogether, which results in the whole file being tried to be parsed. This may yield wrong results in case you are combining centerline data and surface data in one source file.

Compiling and running

You can compile the progam by just invoking "make". The resulting binary should be usable as-is. In fact it can be compiled by g++ and has no library dependencies (aside from the default ones).
The current version, invocation and available options can be retrieved with option -h.

Integrating the results back into therion

One main use case for me was that i wanted to convert the existing DEM from the Hirlatz/Dachstein into survex so i can take exact measurements of cave tunnels to the surface. However it is also very convinient to take measurements from different points of the surface (like heights of walls or distances from peaks).

Combine using therion native format (-t option)

Since V.1.0 the preffered way is to directly export a native therion surface mesh. This can be activated either by ending the output file parameter -o with a name ending in .th or by explicitely requesting the -tparameter.
Exporting directly to therion native format allows you more fine control than to combine survex .3d files.

A short example may be a single thconfig file like this:

source myCave.th
source mySurface.th

export model -o myCave_with_mySurface.3d

Combining several survex/aven 3d-files

Integration is easy, once you know how it works. You need to prepare some therion source file to import your 3d file. See the therion book fo examples.
(this method is needed because aven currently does not support opening several files in parallel in one window).

A short example may be a single thconfig file like this:

source
  import myCave.th.3d -surveys ignore
  import mySurface.3d -surveys ignore
endsource

export model -o myCave_with_mySurface.3d

Alternatives

Survex 1.2.18 added support for loading terrain data and rendering it as a transparent surface in aven. As far as i know this is similar to therions loch terrain feature, where a transparent height model is displayed.
However neither of both viewers currently support the distinct selection of points on the surface, so no measurements can be taken.