fixed points in survex

[Lev Bishop]

On Thu, 6 Feb 2003, John Halleck wrote:

>   But, of course, the effects of not correcting for tape sag overwhelm
>   many of the effects that have been discussed in this thread.
>   How many cave surveyors do that correction?  (And of those that do,
>   how many do the tape temperature correction?)

I thought about tape sag compensation. It wouldn't be hard to do but the 
correction would only be valid while the tape was clean - as soon as the 
tape gets covered in mud and water, its weight per unit length changes and 
the corrections are invalid. The temperature compensation would be 
conceptually easier to implement, but requires an extra measurement. 

On the other hand, a significant number of surveyors are switching to
laser rangefinders instead of tapes (for reasons of convenience, mainly,
rather than accuracy) where tape sag and temperature compensation are no
longer an issue (there are new errors relating to temperature, pressure
and humidity changing the refractive index of air and hence the apparent
range - I don't have figures to hand, I believe this would be a 
very small effect).

Lev