Graham, I too have used declination 0 on the "grid-aligned" data. That's fine when there is no cs setting; but when cs is used, for example when we integrate Upper Flood into the Cheddar Catchment project, Therion rotates the survey by 0.55 degrees to allign True North to Grid North. How can I tell Therion that my survey is already alligned to Grid North rather than True North? Ideally I'd like to do this at the highest level, rather than at the individual survey level, as there are about 50 surveys that make up Upper Flood. The layout setting of North Grid or North True doesn't help either. It is about the alignment of the survey to the grid, and it affects the grid references of the stations. The further from the fixed entrance (as the crow flies) the larger the error of course. Regards, - Ben

-----Original Message----- From: therion-bounces@speleo.sk [mailto:therion-bounces@speleo.sk] On Behalf Of Graham Mullan Sent: 17 February 2011 11:48 To: therion@speleo.sk Subject: [Therion] grid alignment rotation

Ben

We've had similar problems, notably with some of Willie's data where he applied a correction that encompassed both compass error and declination. The result suggested was to insert a line

declination 0 degree

which zero's the declination correction. One can then add a line such as

calibrate compass +11.5

in our circumstances, not needed in yours where the alignment with grid north has already been made.

As far as UFS is concerned, it's also worth noting that Therion recognises the local grid so you can use

cs: OSGB:ST

Graham

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