28 Jul
2008
28 Jul
'08
1:04 p.m.
Martin Budaj wrote:
The grid north is usually not the same as the true (astronomical) north, but for the purposes of cave maps and Therion I would assume it is usually considered to be so. (Not strictly correct, but I imagine the error would not be detectable on any printed cave map in most co-ordinate systems)
The difference is up to 3 degrees for UTM projection or up to 10 degrees for Czech Krovak projection.
I would add to Martin explanation that while the meridian convergence is fixed (for a given location), the declination varies significantly with time. So if you are managing a cave survey project for say, 10 or 20 years... then the difference in declination will be significant (can be several degrees) Eric.