Cave surveying - 2D and 3D drawing software

 Therion aids the process of drawing up cave surveys (maps). Drawings are
 done over scans and can be distorted to fit the centreline data. Output is
 in single sheet or atlas style PDF or SVG files. All data is stored in text
 files and a map editor (xtherion) is provided to aid in the creation of the
 files. A wide range of co-ordinate systems is supported.
 .
 Therion can also produce 3D models, generated from walls and
 passage-heights. Output formats supported are Survex .3d files, VRML, DXF,
 SVG, shapefiles, and the native .lox. Scanned map overlays and relief data
 can be incorporated into models. Therion is compatible with Survex, and
 centreline data can be stored in Survex or Therion form. If survex is
 installed it is used for loop closures. Centreline data and sketches can be
 imported from PocketTopo, allowing full paperless surveying.
 .
 TeX and metapost are used to generate the images. libtk-img is needed to use
 scans in formats other than GIF and PNM (such as PNG and JPEG).
 Survex will be used for loop-closure if installed, but is not required.
 .
 You will need appropriate TeX language packages to process therion files which
 specify those character sets: texlive-lang-czechslovak is needed to process
 the examples, and texlive-lang-cyrillic is also suggested. See README.Debian
 for details.