South Polar Stereographic Projection not producing right plot

Inizia eseguendo plot_field_pole.py con heff.H1987.nc sia per l’argomento S sia per l’argomento N, come descritto nell’issue. Confronta i percorsi spstere e npstere di Basemap, concentrandoti sul risultato di pcolormesh. Il lavoro è completato quando la South Polar Stereographic projection produce un grafico colorato correttamente anziché un grafico a tinta unita.

Hi,

This may be a followup of a previous closed issue (https://github.com/matplotlib/basemap/issues/118).
I am making polar stereographic projection pcolormesh plots of some sea ice data. It works fine with the Northern Hemisphere, but produces solid color for the South.
The problem was replicated on both Linux and Windows with different versions of Python, numpy, matplotlib and basemap. I am using basemap-1.1.0 with matplotlib-1.5.3 in winpython-3.5 on Windows 10 to produced the following figures.
Here is an example script:

from netCDF4 import Dataset
import matplotlib
import matplotlib.pyplot as plt
import numpy as np
import array
import matplotlib.cm as cm
from mpl_toolkits.basemap import Basemap
import glob
import struct
import datetime
import time
import sys
from pylab import *


POLE=sys.argv[3]
fname=sys.argv[1]
fld=sys.argv[2]
print(fname)
ncfile = Dataset(fname, 'r', format='NETCDF4')
fbot=ncfile.variables[fld][0]
if 'lon' in ncfile.variables:
    LON=ncfile.variables['lon'][:]
if 'lon_scaler' in ncfile.variables:
    LON=ncfile.variables['lon_scaler'][:]    
if 'LON' in ncfile.variables:
    LON=ncfile.variables['LON'][:]
if 'lat' in ncfile.variables:
    LAT=ncfile.variables['lat'][:]
if 'lat_scaler' in ncfile.variables:
    LAT=ncfile.variables['lat_scaler'][:]    
if 'LAT' in ncfile.variables:
    LAT=ncfile.variables['LAT'][:]
if 'kmt' in ncfile.variables:
    kmt=ncfile.variables['kmt'][:]

lon=LON
lat=LAT
    
if len(LON.shape) == 1:
    lon,lat=np.meshgrid(LON,LAT)

if 'kmt' in ncfile.variables:
    fbot=ma.masked_where(kmt<1, fbot)
    
ncfile.close()

meridians=[1,0,1,1]

fig=figure(figsize=(12,12), facecolor='w')

if  POLE=='N':
    m = Basemap(projection='npstere',lon_0=0,boundinglat=45)
if  POLE=='S':
    m = Basemap(projection='spstere',lon_0=180,boundinglat=-45)
m.drawcoastlines()
m.fillcontinents()
m.drawcountries()
plt.title(fld)
x, y =m(lon,lat)
m.pcolormesh(x,y,fbot,vmin=float(sys.argv[4]), vmax=float(sys.argv[5]))
m.drawparallels(np.arange(-90.,120.,15.),labels=[1,0,0,0]) # draw parallels
m.drawmeridians(np.arange(0.,420.,30.),labels=meridians) # draw meridians
plt.colorbar(orientation='vertical',extend='both',shrink=0.8)
plt.show()

A netcdf file to reproduce the problem can be downloaded here

ftp://pscftp.apl.washington.edu/zhang/Global_seaice/heff.H1987.nc.gz

Once untared, the following call to the above script (named plot_field_pole.py)

python plot_field_pole.py heff.H1987.nc heff S 0.0 3.0

will give the wrong plot.

while

python plot_field_pole.py heff.H1987.nc heff N 0.0 3.0

produced correct one.

The only difference between the two commands is Basemap(projection='spstere') or
Basemap(projection='npstere')

Any help will be much appreciated.

Bin Zhao