[Matplotlib-users] Robinson projection imshow out of bounds and different latitude limits

[Sebastian K. <seb...@io...>]

Dear all!

I would like to ask two questions: one concerning imshow with the 
Robinson projection and the second about the latitude limits for the 
same map projection.

First, I am trying to make a Robinson projection map using imshow 
instead of contourf as described in the Basemap documentation. I 
modified the script as follows:

    #----------------------------------------------------------------------
    from matplotlib.toolkits.basemap import Basemap, shiftgrid
    from pylab import load, meshgrid, title, arange, show, cm, pi
    #
    # read in topo data (on a regular lat/lon grid)
    etopo = load('etopo20data.gz')
    lons  = load('etopo20lons.gz')
    lats  = load('etopo20lats.gz')
    #
    # create Basemap instance for Robinson projection.
    m = Basemap(projection='robin',lon_0=0.5*(lons[0]+lons[-1]))
    #
    # compute native map projection coordinates for lat/lon grid.
    etopo, lons = shiftgrid(180., etopo, lons, start=False)
    x, y = m(*meshgrid(lons,lats))
    dx = 2.*pi*m.rmajor/len(lons)
    nx = int((m.xmax-m.xmin)/dx)+1; ny = int((m.ymax-m.ymin)/dx)+1
    dat, x, y = m.transform_scalar(etopo, lons, lats, nx, ny, returnxy=True)
    #
    # make filled contour plot.
    im = m.imshow(dat, cmap=cm.jet)
    m.drawcoastlines() # draw coastlines
    m.drawmapboundary() # draw a line around the map region
    m.drawparallels(arange(-90.,120.,30.),labels=[1,0,0,0]) # draw parallels
    m.drawmeridians(arange(0.,420.,60.),labels=[0,0,0,1]) # draw meridians
    title('Robinson Projection') # add a title
    show()
    #----------------------------------------------------------------------


The result looks as I would expect, except that some data is plot 
outside of the map boundaries. Using another projection as the 
Orthographic for example, this problem doesn't happen. Am I doing 
something wrong?

Second, I work with Topex/POSEIDON and Jason-1 sea surface height 
anomalies datasets where the latitudes range from about 67.5S to 67.5N. 
Outside these limits hopefully its blank, as anyone would expect. 
Aesthetically I find it more appealing if I could limit my map 
boundaries to these limits, or even lower limits if I zoom the 
equatorial region. Has anyone ever tried to do this?

Thank's in advance and kind regards,
Sebastian