Other Cave Software

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Comparison of Tunnel to Other Cave Software

The following cave drawing projects are designed to tackle the same unique set of difficulties of loop closures and passage crossings.


Therion is similar to Tunnel in that both were originally built on top of Survex. Therion is a complex evolution of Tcl which pipes its output through Metapost.

Unfortunately, Therion and Tunnel use fundamentally different geometric models, so the two systems are not compatible. If they were, you could use whichever user interface you liked best, and the data structure and rendering would be the same underneath.

The main distinction between the two systems is that Tunnel copies them pieces your cave survey pieces which you then edit, while Therion leaves your original drawings in place and attempts to glue them together automatically.

The original design of Tunnel (conceived independently) was intended to be more Therion-like, but its implementation fell short due to what appeared to be insurmountable practical difficulties in the Therion approach, leaving it in the theoretically inferior state it is today.

In Tunnel, a drawing of a survey is called a sketch, while in Therion it's called a scrap. In Tunnel, the drawing of the whole cave is still a sketch -- a large one that everything has been copied into -- while in Therion the structure that groups scraps together is called a map.

There is a trade-off between the simplicity of the lack of hierarchy in Tunnel and the ease with which it is possible to build features upon it.

The disadvantages of Tunnel's way are as follows:

  1. You have to do a lot of extra editing just to join in a new piece of the survey.
  2. You wind up with multiple copies of the same piece of cave in your workspace.
  3. You lose the connection to the original drawings so you can't correct them in the original state and see the changes in the final drawing.
  4. It's not known how many times a survey could be copied and morphed before unexpected errors of distortion would become a problem.
  5. The files for a large survey can become rather large.

These points can be considered in turn.

1. The idea that a computer can be programmed to automatically stitch together the ragged ends of two surveys quickly loses its believability once you see the data that you actually get from cavers. Often there are huge overlapping inconsistent sections, or gaps between adjacent surveys. In practice, Therion users have to do extensive work to clean up these joins before the computer can do it automatically. The process is inherently harder than in Tunnel because you are having to edit two separate drawing structures at the same time.

2. The problem of multiple copies has looked bad, but has successfully been ignored.

3. original sketches are done by tracing survey images in the first place. Unlike, for example, transcribing the text of a scanned document, it's rare to trace an image wrongly. Since corrections to the original hand-drawn survey notes never happen, it's unlikely one would want to change its corresponding tracing. You can make corrections to mistakes discovered after the sketches have been copied and merged, or even delete portions and replace them with more accurate surveys, but these changes have little to do with whether you need to change the tracings of the original pencil drawings.

4. if there does appear to be a problem after too many generations of the same sketch, it is conceivable to throw it all away and re-import all the sketches again from the originals, and stitch them together. This would be a lot of work, but it is the back-up plan.

5. large parts of a Therion map need to be in the computer's at the same time in order to work out any joining problems. Super-large cave systems haven't been tackled in Tunnel yet, but there are plans to break up the files into manageable tiles when things get out of hand.

Differences between the user interfaces not due to the underlying complexities of the data structure can't be commented upon because they can change quickly. At the moment, Tunnel's boulder layout is said to be superior to Therion's, but theirs could suddenly improve tomorrow if they reimplemented it.

There is a facility to import individual Therion scraps into Tunnel as sketches. Whether this can be made to work well enough is not yet known.


The name "Walls" is an even worse name for a program than "Tunnel", in terms of finding it using a search engine. Here is the Walls Manual.

Like Tunnel, Walls can write SVG files and distort cave sketches (the feature is called "Roundtripping SVG maps"), and is documented in the manual.

It's implementation is likely to be compromised by the lack of connectivity between the centreline and the walls. The connective lines between the survey stations and nodes in the walls that you need to add in Tunnel are a hassle at the time, but once your cave becomes a huge structure with passages crossing over in every direction, you can't do without it.

The alternative strategy of keeping separate zones of the caves in different 2D drawings that are distorted independently and super-imposed in the final image works well if you know the general layout of the cave before you start surveying it, or you are lucky.