From: Jeff Whitaker <jswhit@fa...>  20071011 17:49:55

Adam Mercer wrote: > Hi > > I'm running into a problem using the mollweide projection, with the > following simplified code, my actual code doesn't use random data for > values but this is a clearer example to the problem I'm experiencing: > > lon = numpy.arange(0, 361, 1) > lat = numpy.arange(90, 91, 1) > x, y = numpy.meshgrid(lon, lat) > values = numpy.random.random((181, 361)) > > map = basemap.Basemap(projection='moll', lon_0=0, resolution='c') > map.drawcoastlines() > map.drawcountries() > map.drawmapboundary() > map.drawmeridians(numpy.arange(0,360,30)) > map.drawparallels(numpy.arange(90,90,30)) > > X, Y = map(x, y) > > map.contourf(X, Y, values) > > I get the following error: > > WARNING: x coordinate not montonically increasing  contour plot > may not be what you expect. If it looks odd, your can either > adjust the map projection region to be consistent with your data, or > (if your data is on a global lat/lon grid) use the shiftgrid > function to adjust the data to be consistent with the map projection > region (see examples/contour_demo.py). > > And the resulting map is incorrect due to the horizontal trends, see > http://tier2.ihepa.ufl.edu/~ram/files/moll.jpg > > > but if I use the orthographic projection ie: > > map = basemap.Basemap(projection='ortho', lat_0=20, lon_0=30, resolution='c') > > Then there are no errors, and the map is displayed as expected, see > http://tier2.ihepa.ufl.edu/~ram/files/ortho.jpg > > I am unsure as to why I am receiving this error for the mollweide > projection, as my coordinate grid is covering the entire surface. I > am clearly doing something wring here but I don't know what  does > anyone know what is causing this issue? > > Cheers > > Adam > Adam: I assume your data is on a latitudelongitude grid? You've asked for a mollweide projection centered on the Greenwich meridian. Your data is not centered on Greenwich  but the error message is trying to say that you can shift your grid (with the shiftgrid function) so that is has the same orientation as the map projection region. This only comes into play with global projections that 'wraparound' at the edges, like the mollweide and mercator projections. The orthographic projection does not 'wrap around'  hence you don't get the error message. Jeff  Jeffrey S. Whitaker Phone : (303)4976313 Meteorologist FAX : (303)4976449 NOAA/OAR/PSD R/PSD1 Email : Jeffrey.S.Whitaker@... 325 Broadway Office : Skaggs Research Cntr 1D124 Boulder, CO, USA 803033328 Web : http://tinyurl.com/5telg 