Cave-Surveying Digest, Vol 12, Issue 1

[Eric Madelaine, INRIA]

Pat Kambesis a écrit :
> I think the reasoning behind going for longer shots instead of shorter ones is that with fewer survey stations, it is statistically possible to make fewer errors.  

This sounds like a deep misunderstanding of statistics, doesn't it ? The 
more stations you have, th elowest overall error...

> However the longer the shot, the more difficult it is to site accurately.  Digital instruments can greatly minimize user error since the reader doesn't have to assume contorted positions to read the shot and  are a lot easier to learn to use accurately than suuntos.
>
> Regardless of which types of instruments are used (digital vs analog), the biggest limitation on the survey  is the speed (or rather efficiency) of the sketcher.  Even if one could shoot accurate 100 meter long legs, the sketcher still needs time to accurately record data and make the sketches (sketching to scale in plan, profile, cross sections).  "Eyeballing" a very long shot in terms of making the sketch i.e. no distance reference, is very difficult with shots that are much longer than 30 meters - one can't "eye" estimate where to place passage/wall details with much accuracy with distances greater than 15 meters (my personal experience).
>   

My experience is that the most significant parameter (for a given 
instrument and a given operator) is the materialisation of the survey 
station. I would strongly argue that if you go for a precise laser 
instrument that is capable of precise measures (length _and_ angles), 
then you _must_ use some kind of physical artifact for the stations, 
being a reflector on a tripod if you can, or any kind of substitute...
The problem of indentifying the point foe laser lenght measures that 
wookey mentionned is solved at the same time...

In that case, I think that indeed we can use much longer legs with accuracy.
And of course you are correct, this applies only to the survey skeleton, 
so it may be perfect for outside surveys, while cave survey with 
accurate drawings (like useful input for therion...) implies short legs, 
and survey station carefuly chosen, and meaningful with respect to the 
cave volume.

Eric Madelaine