On 27/12/2021 19:41, Tarquin Wilton-Jones via Therion wrote:
But because DistoX is an electronic device it is only way to be sure it
works properly. The same as check, if three (four) readings for
surveying leg with rotation around the longitudinal axe of DistoX are in
tolerance interval.
Oh very true. This is one of the checks I recommend performing
occasionally to test calibration (or every leg when working around
scaffolding or magnetic rocks). Create legs with one reading flat, one
rotated 90 degrees longitudinally, another reading flat or in any other
orientation. Then validate with a splay back to the previous station.
I think, but have no proof, that if you rotate the distoX it is probably
better than a manual backsight. pockettopo records the rotation, and I
have this in the therion file. People surveying with me know I check
that they rotate at least every 5 stations and i relity they rotate most
station. All the times I've been with people doing backsights (mainly US
cavers) all it seems to stop is blunders, if they don't get a reading
that is within their personal tolerance they do it all again. The real
question is how much are they doing expectation bias? I cannot really
comment further as I have too little experience of this.
On 27/12/2021 19:36, Bill Gee wrote:
I remember seeing a presentation at a recent NSS Convention (2020, maybe?)
where someone took an uncalibrated DistoX2 and ran it around a survey course on
the surface. By averaging the forward and backward shots he got loop closures
around 1% over 400 feet and a dozen stations. The data using Suunto/tape and a
calibrated DistoX2 was not significantly different in the loop closure.
A compass that is 10° (well any degrees off will give a 0% loop error,
the longer the loop the lower the percentage error, however bad the
survey. (bit of over simplification, but relatively true) High percent
loop closure is a poor survey, the opposite is not true.
This could turn into a long interesting debate, please feel free to
argue with me, let's see how robust our ideas are :-)
Andrew
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