I might understand something wrong, but it seems to me, that 

what is called `cavelength` in Therion is actually the length of all centerlines.

This might correspondent to the cave length in straight caves but certainly not in labyrinth like caves.

I was told about the "Kluterthöhle" in germany which was surveyed in the 60ies to ca. 5900 m and then

resurveyed and recalculated - to have only a length of 5200 m or so.

This is for on the one hand a problem with circular shots inside big rooms, like http://filez.foxel.org/3s3H0d2X361A0K222Z3N 

An other problem are crossroads like http://filez.foxel.org/1t0C0r2Q011i0g1L0i00 where you can't young the shared area of two passages twice but must - at least to what I have been thought - deduct some part of the centerlines: in the following picture I have marked the parts being considered cavelength yellow and the centerlines not counting as part of the cavelength red https://img.skitch.com/20120221-jhraj625isy8j1i9naxiki3b76.png

Certainly I'm not the first person stumbling about this.

What is the preferred way to approach the calculation of cave lengths?

Regards

Maximillian