import pylab as p
from matplotlib.toolkits.basemap import Basemap as Basemap
# Tissot's Indicatrix (http://en.wikipedia.org/wiki/Tissot's_Indicatrix).
# These diagrams illustrate the distortion inherent in all map projections.
# In conformal projections, where angles are conserved around every location,
# the Tissot's indicatrix are all circles, with varying sizes. In equal-area
# projections, where area proportions between objects are conserved, the
# Tissot's indicatrix have all unit area, although their shapes and
# orientations vary with location.
# adapted from http://www.perrygeo.net/wordpress/?p=4
m = Basemap(llcrnrlon=-180,llcrnrlat=-80,urcrnrlon=180,urcrnrlat=80,
projection='cyl')
shp_info = m.readshapefile('tissot','tissot',drawbounds=True)
for nshape,seg in enumerate(m.tissot):
xx,yy = zip(*seg)
p.fill(xx,yy,'green',zorder=10)
# draw meridians and parallels.
m.drawparallels(p.arange(-90,91,30),labels=[1,0,0,0])
m.drawmeridians(p.arange(-180,180,60),labels=[0,0,0,1])
m.drawcoastlines()
m.fillcontinents()
p.title('Tissot Diagram - Cylindrical Equal Area')
p.show()
m = Basemap(llcrnrlon=-180,llcrnrlat=-70,urcrnrlon=180,urcrnrlat=70,
projection='merc',lat_ts=20)
shp_info = m.readshapefile('tissot','tissot',drawbounds=True)
for nshape,seg in enumerate(m.tissot):
xx,yy = zip(*seg)
p.fill(xx,yy,'green',zorder=10)
# draw meridians and parallels.
m.drawparallels(p.arange(-90,91,30),labels=[1,0,0,0])
m.drawmeridians(p.arange(-180,180,60),labels=[0,0,0,1])
m.drawcoastlines()
m.fillcontinents()
p.title('Tissot Diagram - Mercator Conformal')
p.show()
m = Basemap(lon_0=-60,lat_0=45,projection='ortho')
shp_info = m.readshapefile('tissot','tissot',drawbounds=False)
for nshape,seg in enumerate(m.tissot):
xx,yy = zip(*seg)
if max(xx) < 1.e20 and max(yy) < 1.e20:
p.fill(xx,yy,'green',zorder=10)
m.drawcoastlines()
m.fillcontinents()
m.drawparallels(p.arange(-90,91,30))
m.drawmeridians(p.arange(-180,180,30))
p.title('Tissot Diagram - Orthographic')
m.drawmapboundary()
p.gca().set_frame_on(True)
p.show()
m = Basemap(lon_0=270,lat_0=90,boundinglat=10,projection='npstere')
shp_info = m.readshapefile('tissot','tissot',drawbounds=True)
for nshape,seg in enumerate(m.tissot):
xx,yy = zip(*seg)
p.fill(xx,yy,'green',zorder=10)
# draw meridians and parallels.
m.drawparallels(p.arange(-90,91,30),labels=[1,0,0,0])
m.drawmeridians(p.arange(-180,180,30),labels=[0,0,0,1])
m.drawcoastlines()
m.fillcontinents()
p.title('Tissot Diagram - North Polar Stereographic Conformal')
p.show()
m = Basemap(lon_0=270,lat_0=90,boundinglat=10,projection='nplaea')
shp_info = m.readshapefile('tissot','tissot',drawbounds=True)
for nshape,seg in enumerate(m.tissot):
xx,yy = zip(*seg)
p.fill(xx,yy,'green',zorder=10)
# draw meridians and parallels.
m.drawparallels(p.arange(-90,91,30),labels=[1,0,0,0])
m.drawmeridians(p.arange(-180,180,30),labels=[0,0,0,1])
m.drawcoastlines()
m.fillcontinents()
p.title('Tissot Diagram - North Polar Lambert Azimuthal Equal Area')
p.show()
