Hi everyone
I have had to use Discovers transform Coordinates module to get the projection clause
for a local grid to put into Mapinfo's .prj file in a few projects recently. My
question is on the potential errors in the coordinate transformation. The client
gives me a table of control points in both AMG and local grid, then I create the
affine projection clause for the local grid based on the AMG zone. Once I have the
clause I then check the accuracy of the transformation by creating points in AMG using
the control point file. I then change the map projection to newly created local grid
projection using Map Options and snap the cursor to one of the points. This allows me
to compare the coordinates in local grid given by the cursor position on screen to the
actual local grid coordinates in the control file. In the past few projects I have
come up with errors from 0.5m to around 7metres using this method, all points are
shifted by trhe same amount and in the same direction. I get a different result if I
use only a selection of control points.
Can you give me any idea what would cause this error? - the clients are convinced
their control points are correct as they were surveyed in.
I am using Mapinfo 6.5 and Discover 3.097 on a Windows 2000 PC with 1GB of Ram.
Thanks
Steve King
