Therion is intended for drawing caves, not surface maps. In general, it relies on the surface image and topographical data for showing the surface. However, you may wish to include surface features, such as dolines, buildings, trees, roads, paths, etc. on your survey, without having to add the noise of a satellite image.

Include these surface features in your surface survey legs, so that you can precisely pinpoint their location. (Alternatively, you can trace over a satellite image in XTherion, as long as you can fix at least one position on your survey relative to that image. Note, however, that surface surveys are often a lot more accurate than satellite images, as the satellite image gets warped by the angle the image is taken from, and the shape of the landscape. Even relatively accurate approaches for stretching images back over their landscape fail quite significantly to match the actual landscape, particularly if trees are involved, as they cause most popular LIDAR scans to get the wrong altitudes. But I digress…)

Open the data rendered as an image (eg. a Therion XVI file) in XTherion's map editor, exactly like you would with a cave passage. Create scraps using the survey stations, exactly like you would with a cave passage. Draw on the features you wish to show (a circular “slope” makes a great doline, pitch lines are good for cliffs, and a “border” can be used to outline roads, paths and buildings - a “temporary” border subtype even gets rendered as a dashed line like a path may appear on a regular outdoor map - and fill areas if desired to show rivers, lakes or forests). Avoid using “wall” lines (unless you set their “outline” to “none”), because that will make Therion assume you are in a cave, which causes it to draw weird shapes on any .lox files, and add altitude highlights or foreground fills to your surface on any PDF files.

But here comes the confusing part; when you ask Therion to include these scraps in your drawing, most of these features do not show up, because they are not inside a “cave” passage.

In XTherion, right click on the lines you have drawn. Select “other options” - “clip” - “off”, or manually set the “-clip off” option in the Lines panel. The lines will now be allowed to appear outside of any cave passages. For best results, keep your surface features within dedicated surface scraps and maps (rather than drawing them in as part of your cave's scraps/maps), so that they can be excluded or included from the resulting PDF output as desired.

Certain surface features do not have any nice way to represent them, however, such as a tree that is used as a natural belay for a pitch. These can be created as a symbol using MetaPost. Consider creating your own symbols using MetaPost (and share them with the rest of us, please). Or if it is large enough, draw it manually using borders, and try making it look nice. Good luck, and happy sketching.

Note that it is not easily possible to ask Therion to shade the ground in one colour and the sky in another (when drawing elevations through a mountain, for example). To do that, you would have to draw the surface as a “cave” wall, and draw an opposing “wall” below the altitude of the actual walls of the cave, and use “break” to place it behind all of the actual caves. Then style that scrap with the colour of your choice. It is messy though. An alternative approach is to outline the surface and sky using a border, then fill it with a “u” area, where you have defined a subtype to fill in the sky with a blue colour using MetaPost. Set the border to “-visibility off”. If you have any other solutions to this problem, please share them here.

  • surfacefeatures.txt
  • Last modified: 4 years ago
  • by tarquinwj