hexbin_demo.py

from __future__ import (absolute_import, division, print_function)

# example showing how to plot scattered data with hexbin.
fromnumpy.randomimportuniform
importmatplotlib.pyplotasplt
importnumpyasnp
frommpl_toolkits.basemapimportBasemap

# create north polar stereographic basemap
m=Basemap(lon_0=270, boundinglat=20, projection='npstere',round=True)
#m = Basemap(lon_0=-105,lat_0=40,projection='ortho')

# number of points, bins to plot.
npts=10000
bins=40
# generate random points on a sphere,
# so that every small area on the sphere is expected
# to have the same number of points.
# http://mathworld.wolfram.com/SpherePointPicking.html
u=uniform(0.,1.,size=npts)
v=uniform(0.,1.,size=npts)
lons=360.*u
lats= (180./np.pi)*np.arccos(2*v-1) -90.
# toss points outside of map region.
lats=np.compress(lats>20, lats)
lons=np.compress(lats>20, lons)
# convert to map projection coordinates.
x1, y1=m(lons, lats)
# remove points outside projection limb.
x=np.compress(np.logical_or(x1<1.e20,y1<1.e20), x1)
y=np.compress(np.logical_or(x1<1.e20,y1<1.e20), y1)
# function to plot at those points.
xscaled=4.*(x-0.5*(m.xmax-m.xmin))/m.xmax
yscaled=4.*(y-0.5*(m.ymax-m.ymin))/m.ymax
z=xscaled*np.exp(-xscaled**2-yscaled**2)

# make plot using hexbin
fig=plt.figure(figsize=(12,5))
ax=fig.add_subplot(121)
CS=m.hexbin(x,y,C=z,gridsize=bins,cmap=plt.cm.jet)
# draw coastlines, lat/lon lines.
m.drawcoastlines()
m.drawparallels(np.arange(0,81,20))
m.drawmeridians(np.arange(-180,181,60))
m.colorbar() # draw colorbar
plt.title('hexbin demo')

# use histogram2d instead of hexbin.
ax=fig.add_subplot(122)
# remove points outside projection limb.
bincount, xedges, yedges=np.histogram2d(x, y, bins=bins)
mask=bincount==0
# reset zero values to one to avoid divide-by-zero
bincount=np.where(bincount==0, 1, bincount)
H, xedges, yedges=np.histogram2d(x, y, bins=bins, weights=z)
H=np.ma.masked_where(mask, H/bincount)
# set color of masked values to axes background (hexbin does this by default)
palette=plt.cm.jet
palette.set_bad(ax.get_facecolor(), 1.0)
CS=m.pcolormesh(xedges,yedges,H.T,shading='flat',cmap=palette)
# draw coastlines, lat/lon lines.
m.drawcoastlines()
m.drawparallels(np.arange(0,81,20))
m.drawmeridians(np.arange(-180,181,60))
m.colorbar() # draw colorbar
plt.title('histogram2d demo')

plt.show()