why does pcolor with masked array still fill quadrangles connecting to masked points, and how do I stop this?

Question

To mitigate the problem described here, I\'m trying to draw my pcolor plot in two complimentary parts. I have X and Y data that corre

Answer 1

I see maybe I wasn't clear enough on my quick comment on the other question, but by masking I mean that the grid needs to by masked, not the values.

from numpy import array, ma
import matplotlib.pyplot as plt

lons = array([[ 100.,  120.,  140.,  160.,  180.],
       [ 120.,  140.,  160.,  180., -160.],
       [ 140.,  160.,  180., -160., -140.],
       [ 160.,  180., -160., -140., -120.],
       [ 180., -160., -140., -120., -100.],
       [-160., -140., -120., -100.,  -80.]])

lats = array([[  0.,  10.,  20.,  30.,  40.],
       [  0.,  10.,  20.,  30.,  40.],
       [  0.,  10.,  20.,  30.,  40.],
       [  0.,  10.,  20.,  30.,  40.],
       [  0.,  10.,  20.,  30.,  40.],
       [  0.,  10.,  20.,  30.,  40.]])

bts = array([[ 0,  1,  2,  3,  4],
       [ 5,  6,  7,  8,  9],
       [10, 11, 12, 13, 14],
       [15, 16, 17, 18, 19],
       [20, 21, 22, 23, 24],
       [25, 26, 27, 28, 29]])

fig, (ax,ax2) = plt.subplots(ncols=2)
ax.pcolor(ma.masked_where(lons>0, lons), 
       ma.masked_where(lons>0, lats), 
       ma.masked_where(lons>0, bts))

ax2.pcolor(ma.masked_where(lons<0, lons), 
       ma.masked_where(lons<0, lats), 
       ma.masked_where(lons<0, bts))

plt.show()