Hello all, I'm trying to set up the projection parameters for a local coordinate system. The coordinate system is 'attached' by five points of which I know both lat/long and UTM33 coordinates. It is relatively easy to perform an affine transformation between my local system and UTM33 using v.transform, and the transformation parameters can also easily be found with R (Thanks Dylan for the example at http://casoilresource.lawr.ucdavis.edu/drupal/node/433.) The problems arise when I try to set up the projection with g.setproj (and these probably reflect the fact I'm no geographer). As I have understood, I should set the +proj and +towgs84 parameters. The latter reflects the affine transformation coefficients (rotation, scale, transformation), but relative to what should they be calculated? And what should the +proj parameter then be, considering that the geometrical shape on which the local system is based is actually a flat surface? Since I have the 'real' coordinates in UTM33, I considered the following:
+proj=UTM +zone=33 +towgs84=dx,dy,dz,rx,ry,rz,scale where the +towgs84 coefficients come from the affine transformation matrix between my coordinates and UTM33 coordinates. But the results are, well, less than right... And I'm quite at loss how to go on further. Harri K. _______________________________________________ grassuser mailing list [email protected] http://grass.itc.it/mailman/listinfo/grassuser
