[Proj] Lat-Lon values under different ellipsoides

Duncan Agnew dagnew at ucsd.edu
Mon Jan 26 13:21:59 EST 2009


         I would say that it is better not to have a different ellipsoid
change the ellipsoidal coordinates (which is what lat/long are).

         It may also be that you are looking at the difference betweeen
astronomical latitude and geodetic. The latter is what you get if the
reference for the local vertical is the normal to the ellipsoid; the
former, easier to do, assumes the local vertical is the direction of the
plumb line. The difference is the deflection of the vertical, which 
on the slope of the geoid: I don't know what this is for the 
It is quite possible that the 1850 values are astronomical: you'd need 
expert on local geodetic history to find out

Duncan Agnew

More information about the Proj mailing list