I've had some problems getting mapproject() in the mapproj package in R to give me the same projection as one gets from PROJ.4 or ArcGIS. Basically, I can't get the same projected coordinates in mapproject as I do with the standard packages.
For example, I'd like to project with the Albers projection, with central meridian -96, standard parallels 29.5 and 45.5, and latitude of origin 23.0, with false_easting and false_northing both zero, and units of meters. In mapproject, I can use orientation=c(90,0,-96) or orientation=c(90,-96,0), and it will put the central meridian at -96 but I have no control over where y=0 falls (which I think should be based on the latitude of origin) nor of the scaling of the projection. Using one of the orientations above, the Albers projection in mapproject is a linear transformation of the true Albers projection (-96,29.5,45.5,23). If anyone understands better what mapproject() is doing and how to control it, I'd love to hear it.
A solution to this is to explicitly use PROJ.4; this could even be done within R by using the system() function, but of course requires that you have PROJ.4 on your machine.
Last modified: 6/23/07.