hi, I've been reading your post because I want to do a cave 3D mapping and was looking for a cheap and easy solution;
my first idea was same as yours, use a laser distace meter in some way with a computer to read the data and turn it 360 degrees and move tru the cave and later with software make up the map of the cave;
my first idea was to have a long rail that the laser would move along stoping every 20 cm or so to scan and storring or sending back by wifi the data to laptop in control; rail could be shorter or longer by adding more segments and new direction would be mesured the new angle x-y in some way.
I found this simple proyect with a phone cam and laser pointer with arduino that might work fast;http://diydrones.com/profiles/blogs/11-gram-arduino-powered-laser-rangefinder
takes 2 photos first with laser of next on and only finds the diference in pixels in an array of 96 pixels, simple, basic, but I think is a good start, the price must be quite low...
I would change this to 2 laser pointers one more separated than the other and turn them on one after the other and take 3 photos and search for the pixel so it gets more acurate in short and large distance... (or maybe I'm wrong..)
and increase the number of pixels, it will need more process power or/and be slower, but will be more exact,
still think that the idea of a rail betwen 2 tripods is the best idea, and in my case for a real error free I would include a real laser distance meter in the base that controlled the exact distance to the milimeter of the 360 laser system on the rail, if it is in a slope it may stop to short or past the 20/30 cm mark, it would make the rail and moving on it less importan if its not exact because the software can ajust the data later!
to move on the rail a one tracktion weel plus 4 more up and a couple under the rail for stability and maybe a weith under if there is to much weit on top (or the batterys under..) (midle tripods can suport the rail by one side while the "train" has the upper structure joined to the under structure from the other side of the rail.
the laser pointer and cam is mounted on an arm in the front that goes near 360 degrees from the left side of the rail (with a couple of swich sensor to avoid nocking into the tripod) to the other side and rest up or down at the end of the turn, and maybe I would do a side scan also, maybe -30 to +30 degrees, so it gets better data, stoping every 10/15 degrees on the turn and doing on every stop of the turn a side scan at maybe -30, -15, 0, +15 and +30, so it can take in the side holes of the cave in a better 3D way! (it would be much much easier if we had the flying drones of the film Prometheus)
PS: or the tripod can have a magnet so the "train" avoid stopping just there, remember with the main laser distance meter at the base we know were it is at milimeter precision,
what do you think of my idea?
thanks for reading me and sorry for any spelling mistake, I'm from the canary islands