John,
Attached is a script illustrating how to make contourf plots with a log
colorscale. I made some improvements in svn, as noted in the script,
but you can still do it with the regular mpl release. All of this
should carry through to basemap with no changes in basemap.
Eric
John wrote:
Well, it seems like I'm making progress, but it's stll not the plot I'm
hoping to produce. Something seems strange. First, it does create a
contourf plot, but I really need to take log(zdata) and use imshow
(which seems to handly the INF issue, wheras contourf crashes). On
another issue though, once the image is created, when I draw the map
components it covers the image entirely.. so I just see coastlines,
meridians, etc on a whilte background as if I had never plotted the data.
Thanks for helping with this! I'm really trying to make a movement with
my colleagues away from matlab, but I need to have things operating more
smoothly... lately it hasn't been going so well. This is a great product
you've made!
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'''
Demonstrate use of a log color scale in contourf
'''
import pylab as P # or "from matplotlib import pyplot as P" if you are using svn
import numpy
from numpy import ma
from matplotlib import colors
from matplotlib import ticker
z = numpy.arange(10000, dtype=float)
z.shape = 100,100
z = numpy.power(10, 5*z/z.max())
# Put in some negative values to cause trouble with logs:
z[:5, :5] = -1
# The svn version will do the following automatically, and
# print a warning; but with the released mpl you must do it
# yourself.
z = ma.masked_where(z<= 0, z)
lev_exp = numpy.arange(0, numpy.log10(z.max())+1)
print z.max(), z.min()
print lev_exp
levs = numpy.power(10, lev_exp)
# With svn, automatic selection of levels works; setting the
# locator tells contourf to use a log scale:
#cs = P.contourf(z, locator=ticker.LogLocator())
# but with the current mpl release, you must carefully
# set the levels yourself, and set the norm like this:
cs = P.contourf(z, levs, norm=colors.LogNorm())
# Of course the form above still works in svn also.
#The 'extend' kwarg, however, does not work yet with a log
#scale either in the release or in svn.
cbar = P.colorbar()
P.show()
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