[Therion] Turning LIDAR point clouds into cave maps

[Tarquin Wilton-Jones]

> You can do a lot of DistoX2 splays and then try to manually match the
> LIDAR point cloud to the DistoX2 splay model. This is the method I
> used twelve years ago when I was first experimenting - it is very time
> consuming. Now I would suggest you use something that is sufficiently
> large enough to register in the LIDAR cloud that can be surveyed with
> the DistoX2 eg. a large distinctive rock, formation or other natural
> feature or something man-made, tackle bag, container, helmet etc.

I believe this purpose could very easily be served by the "three white 
orbs". (Though the accuracy might not be great, since they are not 
points, so you are hitting somewhere on a surface,  and can't precisely 
locate that.)

But this also then brings out the potential for error when the post 
processing doesn't match the centreline, and one of them has to "win". 
As you said, this is done in mine surveys.

I still wouldn't want to be using Therion to draw up LiDAR data, just 
because there is so much that it becomes unusable. It is already hard 
enough drawing up a survey that has a lot of regular splays because the 
team got over-enthusiastic with the Disto. "Wait, which one of those 
splays points to the pitch edge?". And there is nothing to tell you if 
something is a pitch, a climb, a floor step, or a dangerous pile of 
loose boulders. Point clouds are great for showing fancy fly-throughs 
for non-cavers, and for mining engineers to see exactly how much more 
material they can remove before compromising a wall, but they add a lot 
of confusion for a cartographer. (But again, see Julian's project.)