Therion
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Useful links
- A therion tutorial
- the migovec resurvey project repository (GitHub)
- The Therion Book
- the SURVEX project
- the THERION project
Why choose Therion?
Loop closures
One of the main symptoms of the limitations of Inkscape arises when we need to close a survey loop. We might explore a new branch of cave or resurvey an older part and connect two stations on the mainline. The errors are redistributed all along the branches. Have a look at a .3d file of sistem Migovec coloured by loop closure error and you will see many of the branches have more than 10% error.
When a connection or resurvey is included into our .3d model of the cave, the previously drawn walls of the cave will end up way outside of the centreline survey; therefore they should be rescaled and rotated in a non-trivial way to match the new centreline, a time consuming operation.
In Therion, the walls, pitch head, formations, areas of water or breakdown are tied to the centreline and automatically rescaled and rotated depending on the loop closures. In brief, once a bit of cave is drawn, it rarely needs to be manually redrawn again. This also means cave walls have an altitude attribute and the cave passage elevation can be displayed visually as a colour fill.
Data and its representation
Therion keeps the data (what is there) and its representation (how we should display it) completely separate, hence the need for data files (.th and .th2) and compiler files (th.config*). In Therion, the visualisation of the data is added in METAPOST at a later phase of data processing. In Inkscape, one would simply draw a wall with an arbitrary line thickness, or colour attribute.
A very neat trick on Therion is to choose scale dependent display of some cave features like survey stations or descriptive labels to declutter the small scale surveys;
Modular and flexible display of the cave systems
Choosing what to show and what to hide on the surveys is very flexible on Therion. It is very simple to isolate one part of the cave and display a specific branch. Similarly, a single passage could be displayed with or without survey lines, with different symbols for the water. All this information on how to display the map is located in the .thconfig* file.