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
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