On Sat, Dec 19, 2020 at 1:07 PM Andrew Atkinson <[email protected]> wrote:
> > I would hesitate to use magnetic legs for this > > purpose (there is much uncertainty with the declination as the models > > are not particularly precise, there is a daily variation of declination > > (up to 0.2 degrees!) and there might be local magnetic anomalies). > > In this case the cave comes out in a valley with little gps signal, the > position and orientation was set from the 2 gps positions we could get, > the a traverse to the cave. So I have very little idea how that ties in > with the declination model. I have been assuming that the direction it > gave where OS grid as that is the format of the positions, I have no way > to check this. I have set the declination to 0 to stop date and position > correction. I think this it right, but advice welcome. Ah, that was a reaction to some previous remarks in the discussion: > In places where we haven't been able to get GPS we have used a distox to set up the leg and > I did consider using an approach similar to Andrew’s, ie to calibrate the Theodolite against a magnetic leg ... Martin
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