fixed points in survex

[John Halleck]

I agree, the temerature effect is small.

I personally think that the "clean tape" sag correction on the other
hand would be a lot closer to reality on a dirty tape than the 
totally uncorrected values being used now.



I think our earth tide messages crossed.
I was with a local (Utah) surveyor that does that sort of
thing as I typed.  Loyal Olsen points out for reference, for those
into trivia, that here in Utah (Centerville to be exact), the
current earth tide is causing an acceleration of -0.0193 mGals


> 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
> 
> 
> -- 
> Survex http://lists.survex.com/mailman/listinfo/survex
>