[Therion] Gradient out of range - does not process

[Martin Budaj]

On Sat, Dec 19, 2020 at 1:07 PM Andrew Atkinson <andrew at wotcc.org.uk> 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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