How do I debug problems with NAD27/NAD83 datum shifting?
• Verify that you have the binary files (eg. /usr/local/share/proj/conus) installed on your system. If not, see the previous question. • Try a datum shifting operation in relative isolation, such as with the cs2cs command listed above. Do you get reasonable results? If not it is likely the grid shift files aren’t being found. Perhaps you need to define PROJ_LIB? • The cs2cs command and the underlying pj_transform() API know how to do a grid shift as part of a more complex coordinate transformation; however, it is imperative that both the source and destination coordinate system be defined with appropriate datum information. That means that implicitly or explicitly there must be a +datum= clause, a +nadgrids= clause or a +towgs84= clause. For instance “cs2cs +proj=latlong +datum=NAD27 +to +proj=latlong +ellps=WGS84” won’t work because defining the output coordinate system as using the ellipse WGS84 isn’t the same as defining it to use the datum WGS84 (use +datum=WGS84). If either the in
