On 5/4/10 2:03 PM, Timothy W. Hilton wrote: > Hello matplotlib users, > > I am having trouble understanding the coordinate transformations in > Basemap and pyproj. I have gridded MODIS vegetation data, with upper > left corner and lower right corner given in projection coordinates > (meters). I want to contour the data with Basemap. The data are in a > sinusoidal projection, but the coordinates do not correspond to what > Basemap seems to expect. > > The code below illustrates the problem. Proj translates the upper > left to lat/lon correctly (-92.327237416031437, 30.141972433747089), > while Basemap does not. > > #-------- code -------- > from mpl_toolkits.basemap import Basemap > from mpl_toolkits.basemap import pyproj > > ulm = [-8895604.1573329996, 3335851.5589999999] #upper left, meters > lrm = [-7783653.6376670003, 2223901.0393329998] #lower right, meters > > sinu = pyproj.Proj(proj='sinu', lon_0=0.0, x_0=0.0, y_0=0.0) > m = Basemap(projection='sinu', resolution=None, lon_0=0.0) > > print "ULM: " + str(ulm) > print "Proj: " + str(sinu(ulm[0], ulm[1], inverse=True)) > print "Basemap: " + str(m(ulm[0], ulm[1], inverse=True)) > #----- end code -------- > > This gives: > ULM: [-8895604.1573329996, 3335851.5589999999] > Proj: (-92.327237416031437, 30.141972433747089) > Basemap: (-159.99950210056144, -59.99995206181125) > > I'm sure I'm missing something really simple, but I've read a lot of > documentation and I'm not sure what. > > Many thanks for any help. > > Best, > Tim >
Tim: Basemap is using pyproj under the hood, but only supports a subset of possible proj4 projections. The basemap sinusoidal projection is global - you can't specify a subregion of the globe. I think that's where the discrepancy is coming from. I'm sure there's a way to plot your MODIS data on a global sinusoidal projection - but it will involve transforming the coordinates to the Basemap global sinuosidal coordinate system. -Jeff -- Jeffrey S. Whitaker Phone : (303)497-6313 Meteorologist FAX : (303)497-6449 NOAA/OAR/PSD R/PSD1 Email : jeffrey.s.whita...@noaa.gov 325 Broadway Office : Skaggs Research Cntr 1D-113 Boulder, CO, USA 80303-3328 Web : http://tinyurl.com/5telg ------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
