Pcolor ValueError crash in some cases

[htonchia]

Description

In some cases, pcolor raises a ValueError and crashes when plotting data from one projection to an other.

In the following plots, the data in the original grid are also plotted as a scatter plot at the cells centers.
The two plots at the bottoms of the figures show the original grid plotted in the original projection (PlateCarree) with pcolormesh and pcolor.

I caught the error and removed the artists crashing the plot using the geoaxes.py version from PR #1467 and I got the following plots:

With current version of geoaxes.py (as of February 23rd 2020) we get the following plot before it crashes.

The plots with geoaxes from #1467 differ from the plots from the current version of geoaxes before the crash.
We can see from the scatter plots, that the pcolormesh plots from the current version fo geoaxes are erroneous while the pcolormesh plots from #1467 version of geoaxes fit the data.
In both geoaxes version, the pcolor plots with coords in axis projection are erroneous. It is to be expected as the cells are not wrapped when the coords are given in the axes projection. On the other hand pcolor cannot plot the data with coords in data projection without raising a ValueError.

In conclusion, the fixes in PR1467, one catching the ValueError and the other one hiding the pcolor cells in the axis projection plot, allow pcolormesh to correctly plot the data.
The ValueError in pcolor needs to be investigated.

Code to reproduce

import numpy as np
import matplotlib.pyplot as plt
import cartopy.crs as ccrs


proj=ccrs.LambertAzimuthalEqualArea
plt.figure(figsize=(10,5), constrained_layout=True)
lats = np.linspace(-10, 90, 12) 
lons = np.linspace(-180, 180, 10) 
lons, lats = np.meshgrid(lons, lats)

axproj = proj(central_latitude=-30)

xye = axproj.transform_points(ccrs.PlateCarree(), lons, lats)

xe = xye[..., 0]
ye = xye[..., 1]
z4 = lats[:-1,:-1] * (1 + 0.001 * lons[:-1,:-1])

fig = plt.figure(figsize=(12, 6.4), dpi=100)

fig.suptitle('LambertAzimuthalEqualArea central_latitude=-30 '
             'ValueError exception caught in pcolor')

ax21 = plt.subplot(2, 2, 3, projection=ccrs.PlateCarree())
ax22 = plt.subplot(2, 2, 4, projection=ccrs.PlateCarree())
ax1 = plt.subplot(2, 4, 1, projection=axproj)
ax2 = plt.subplot(2, 4, 2, projection=axproj)
ax3 = plt.subplot(2, 4, 3, projection=axproj)
ax4 = plt.subplot(2, 4, 4, projection=axproj)



ax21.pcolormesh(lons, lats, z4)
ax21.set_title('pcolormesh\n plot in data projection')
ax22.pcolor(lons, lats, z4)
ax22.set_title('pcolor\n plot in data projection')

ax1.pcolormesh(lons, lats, z4, transform=ccrs.PlateCarree())
ax1.set_title('pcolormesh\n coords in data projection')
ax2.pcolormesh(xe, ye, z4)
ax2.set_title('pcolormesh\n coords in axis projection')
ax3.pcolor(xe, ye, z4)
ax3.set_title('pcolor\n coords in axis projection')

for ax in [ax21, ax22, ax1, ax2, ax3, ax4]:
    ax.set_global()
    ax.scatter(
        np.mean(np.array([lons[:-1,:-1],lons[1:,1:]]), axis=0),
        np.mean(np.array([lats[:-1,:-1],lats[1:,1:]]), axis=0),
        50, z4, edgecolors='black',
        transform=ccrs.PlateCarree())
    ax.coastlines(linewidth=0.2)

ax4.pcolor(lons, lats, z4, transform=ccrs.PlateCarree())
ax4.set_title('pcolor\n coords in data projection\n raises a ValueError')


plt.savefig("img/crash_pcolor_caught.png",
                    dpi=100, pad_inches=0)

Traceback

 Traceback (most recent call last):
  File "[path]/lib/python3.7/site-packages/matplotlib/backends/backend_qt5.py", line 508, in _draw_idle
    self.draw()
  File "[path]/lib/python3.7/site-packages/matplotlib/backends/backend_agg.py", line 388, in draw
    self.figure.draw(self.renderer)
  File "[path]/lib/python3.7/site-packages/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "[path]/lib/python3.7/site-packages/matplotlib/figure.py", line 1709, in draw
    renderer, self, artists, self.suppressComposite)
  File "[path]/lib/python3.7/site-packages/matplotlib/image.py", line 135, in _draw_list_compositing_images
    a.draw(renderer)
  File "[path]/lib/python3.7/site-packages/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "[path2]/cartopy/mpl/geoaxes.py", line 460, in draw
    inframe=inframe)
  File "[path]/lib/python3.7/site-packages/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "[path]/lib/python3.7/site-packages/matplotlib/axes/_base.py", line 2647, in draw
    mimage._draw_list_compositing_images(renderer, self, artists)
  File "[path]/lib/python3.7/site-packages/matplotlib/image.py", line 135, in _draw_list_compositing_images
    a.draw(renderer)
  File "[path]/lib/python3.7/site-packages/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "[path]/lib/python3.7/site-packages/matplotlib/collections.py", line 866, in draw
    Collection.draw(self, renderer)
  File "[path]/lib/python3.7/site-packages/matplotlib/artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)
  File "[path]/lib/python3.7/site-packages/matplotlib/collections.py", line 257, in draw
    transform, transOffset, offsets, paths = self._prepare_points()
  File "[path]/lib/python3.7/site-packages/matplotlib/collections.py", line 235, in _prepare_points
    for path in paths]
  File "[path]/lib/python3.7/site-packages/matplotlib/collections.py", line 235, in <listcomp>
    for path in paths]
  File "[path]/lib/python3.7/site-packages/matplotlib/transforms.py", line 2390, in transform_path_non_affine
    return self._a.transform_path_non_affine(path)
  File "[path2]/cartopy/mpl/geoaxes.py", line 211, in transform_path_non_affine
    geom, self.source_projection)
  File "[path2]/cartopy/crs.py", line 221, in project_geometry
    return getattr(self, method_name)(geometry, src_crs)
  File "[path2]/cartopy/crs.py", line 376, in _project_polygon
    return self._rings_to_multi_polygon(rings, is_ccw)
  File "[path2]/cartopy/crs.py", line 626, in _rings_to_multi_polygon
    multi_poly = sgeom.MultiPolygon(polygon_bits)
  File "[path]/lib/python3.7/site-packages/shapely/geometry/multipolygon.py", line 62, in __init__
    self._geom, self._ndim = geos_multipolygon_from_polygons(polygons)
  File "[path]/lib/python3.7/site-packages/shapely/geometry/multipolygon.py", line 197, in geos_multipolygon_from_polygons
    geom, ndims = polygon.geos_polygon_from_py(shell, holes)
  File "[path]/lib/python3.7/site-packages/shapely/geometry/polygon.py", line 509, in geos_polygon_from_py
    ret = geos_linearring_from_py(shell)
  File "shapely/speedups/_speedups.pyx", line 251, in shapely.speedups._speedups.geos_linearring_from_py
ValueError: A LinearRing must have at least 3 coordinate tuples

Please note that maplotlib and shapely have been installed via anaconda, but cartopy sources have been taken from the current code repository on GitHub (february 2020). The crash happens in shapely.

Full environment definition

Operating system

MacOS Mojave 10.14.6

Cartopy version

Sources from the code repository February, 23rd 2020

conda list

# Name                    Version                   Build  Channel
alabaster                 0.7.12                     py_0    conda-forge
appnope                   0.1.0                 py37_1000    conda-forge
astroid                   2.3.3                    py37_1    conda-forge
attrs                     19.3.0                     py_0    conda-forge
babel                     2.8.0                      py_0    conda-forge
backcall                  0.1.0                      py_0    conda-forge
bleach                    3.1.1                      py_0    conda-forge
ca-certificates           2019.11.28           hecc5488_0    conda-forge
cartopy                   0.17.0          py37h6f81845_1010    conda-forge
certifi                   2019.11.28               py37_0    conda-forge
cffi                      1.13.2           py37h33e799b_0    conda-forge
chardet                   3.0.4                 py37_1003    conda-forge
cloudpickle               1.3.0                      py_0    conda-forge
cryptography              2.8              py37hafa8578_1    conda-forge
cycler                    0.10.0                     py_2    conda-forge
dbus                      1.13.6               h2f22bb5_0    conda-forge
decorator                 4.4.1                      py_0    conda-forge
defusedxml                0.6.0                      py_0    conda-forge
docutils                  0.16                     py37_0    conda-forge
entrypoints               0.3                   py37_1000    conda-forge
expat                     2.2.9                h4a8c4bd_2    conda-forge
filelock                  3.0.10                     py_0    conda-forge
freetype                  2.10.0               h24853df_1    conda-forge
geos                      3.8.0                h4a8c4bd_0    conda-forge
gettext                   0.19.8.1          h46ab8bc_1002    conda-forge
glib                      2.58.3          py37h577aef8_1002    conda-forge
icu                       64.2                 h6de7cb9_1    conda-forge
idna                      2.9                        py_1    conda-forge
imagesize                 1.2.0                      py_0    conda-forge
importlib_metadata        1.5.0                    py37_0    conda-forge
ipykernel                 5.1.4            py37h5ca1d4c_0    conda-forge
ipython                   7.12.0           py37h5ca1d4c_0    conda-forge
ipython_genutils          0.2.0                      py_1    conda-forge
isort                     4.3.21                   py37_0    conda-forge
jedi                      0.16.0                   py37_0    conda-forge
jinja2                    2.11.1                     py_0    conda-forge
jpeg                      9c                h1de35cc_1001    conda-forge
jsonschema                3.2.0                    py37_0    conda-forge
jupyter_client            5.3.4                    py37_1    conda-forge
jupyter_core              4.6.3                    py37_0    conda-forge
keyring                   21.1.0                   py37_0    conda-forge
kiwisolver                1.1.0            py37ha1b3eb9_0    conda-forge
lazy-object-proxy         1.4.3            py37h0b31af3_1    conda-forge
libblas                   3.8.0               15_openblas    conda-forge
libcblas                  3.8.0               15_openblas    conda-forge
libcxx                    9.0.1                         1    conda-forge
libffi                    3.2.1             h6de7cb9_1006    conda-forge
libgfortran               4.0.0                         2    conda-forge
libiconv                  1.15              h01d97ff_1005    conda-forge
liblapack                 3.8.0               15_openblas    conda-forge
libopenblas               0.3.8                h3d69b6c_0    conda-forge
libpng                    1.6.37               h2573ce8_0    conda-forge
libsodium                 1.0.17               h01d97ff_0    conda-forge
libtiff                   4.1.0                ha78913b_3    conda-forge
llvm-openmp               9.0.1                h28b9765_2    conda-forge
lz4-c                     1.8.3             h6de7cb9_1001    conda-forge
markupsafe                1.1.1            py37h0b31af3_0    conda-forge
matplotlib-base           3.1.3            py37h11da6c2_0    conda-forge
mccabe                    0.6.1                      py_1    conda-forge
mistune                   0.8.4           py37h0b31af3_1000    conda-forge
more-itertools            8.2.0                      py_0    conda-forge
nbconvert                 5.6.1                    py37_0    conda-forge
nbformat                  5.0.4                      py_0    conda-forge
ncurses                   6.1               h0a44026_1002    conda-forge
numpy                     1.18.1           py37hde6bac1_0    conda-forge
numpydoc                  0.9.2                      py_0    conda-forge
olefile                   0.46                       py_0    conda-forge
openssl                   1.1.1d               h0b31af3_0    conda-forge
owslib                    0.19.1                     py_0    conda-forge
packaging                 20.1                       py_0    conda-forge
pandoc                    2.9.2                         0    conda-forge
pandocfilters             1.4.2                      py_1    conda-forge
parso                     0.6.1                      py_0    conda-forge
pcre                      8.44                 h4a8c4bd_0    conda-forge
pexpect                   4.8.0                    py37_0    conda-forge
pickleshare               0.7.5                 py37_1000    conda-forge
pillow                    7.0.0            py37h918e99a_0    conda-forge
pip                       20.0.2                     py_2    conda-forge
pluggy                    0.13.0                   py37_0    conda-forge
proj                      6.3.0                h773a61f_0    conda-forge
prompt_toolkit            3.0.3                      py_0    conda-forge
psutil                    5.7.0            py37h0b31af3_0    conda-forge
ptyprocess                0.6.0                   py_1001    conda-forge
py                        1.8.1                      py_0    conda-forge
pycodestyle               2.5.0                      py_0    conda-forge
pycparser                 2.19                       py_2    conda-forge
pyepsg                    0.4.0                      py_0    conda-forge
pyflakes                  2.1.1                      py_0    conda-forge
pygments                  2.5.2                      py_0    conda-forge
pykdtree                  1.3.1           py37h3b54f70_1002    conda-forge
pylint                    2.4.4                    py37_0    conda-forge
pyopenssl                 19.1.0                     py_1    conda-forge
pyparsing                 2.4.6                      py_0    conda-forge
pyproj                    2.5.0            py37hf8af742_0    conda-forge
pyqt                      5.9.2            py37h2a560b1_4    conda-forge
pyrsistent                0.15.7           py37h0b31af3_0    conda-forge
pyshp                     2.1.0                      py_0    conda-forge
pysocks                   1.7.1                    py37_0    conda-forge
pytest                    5.3.5                    py37_1    conda-forge
python                    3.7.6                h5c2c468_2    conda-forge
python-dateutil           2.8.1                      py_0    conda-forge
python.app                1.2             py37h0b31af3_1201    conda-forge
pytz                      2019.3                     py_0    conda-forge
pyzmq                     18.1.1           py37h4bf09a9_0    conda-forge
qt                        5.9.7                h8cf7e54_3    conda-forge
qtawesome                 0.7.0                      py_0    conda-forge
qtconsole                 4.6.0                      py_0    conda-forge
qtpy                      1.9.0                      py_0    conda-forge
readline                  8.0                  hcfe32e1_0    conda-forge
requests                  2.23.0                   py37_0    conda-forge
rope                      0.16.0                     py_0    conda-forge
scipy                     1.4.1            py37h82752d6_0    conda-forge
setuptools                45.2.0                   py37_0    conda-forge
shapely                   1.7.0            py37h999ffa5_0    conda-forge
sip                       4.19.8          py37h0a44026_1000    conda-forge
six                       1.14.0                   py37_0    conda-forge
snowballstemmer           2.0.0                      py_0    conda-forge
sphinx                    2.4.3                      py_0    conda-forge
sphinxcontrib-applehelp   1.0.1                      py_0    conda-forge
sphinxcontrib-devhelp     1.0.1                      py_0    conda-forge
sphinxcontrib-htmlhelp    1.0.3                      py_0    conda-forge
sphinxcontrib-jsmath      1.0.1                      py_0    conda-forge
sphinxcontrib-qthelp      1.0.2                      py_0    conda-forge
sphinxcontrib-serializinghtml 1.1.3                      py_0    conda-forge
spyder                    3.3.5                    py37_0    conda-forge
spyder-kernels            0.5.2                    py37_0    conda-forge
sqlite                    3.30.1               h93121df_0    conda-forge
testpath                  0.4.4                      py_0    conda-forge
tk                        8.6.10               hbbe82c9_0    conda-forge
tornado                   6.0.3            py37h0b31af3_4    conda-forge
traitlets                 4.3.3                    py37_0    conda-forge
typed-ast                 1.4.1            py37h0b31af3_0    conda-forge
urllib3                   1.25.7                   py37_0    conda-forge
wcwidth                   0.1.8                      py_0    conda-forge
webencodings              0.5.1                      py_1    conda-forge
wheel                     0.34.2                     py_1    conda-forge
wrapt                     1.12.0           py37h0b31af3_0    conda-forge
wurlitzer                 2.0.0                    py37_0    conda-forge
xz                        5.2.4             h1de35cc_1001    conda-forge
zeromq                    4.3.2                h6de7cb9_2    conda-forge
zipp                      3.0.0                      py_0    conda-forge
zlib                      1.2.11            h0b31af3_1006    conda-forge
zstd                      1.4.4                he7fca8b_1    conda-forge

pip list

[htonchia]

After further analysis it appears that the crash happens when pcolor is not able to transform the path (the grid cell boundary) from the data projection to the target projection.
I guess it is acceptable for pcolor not to be able to transform some paths that cannot be displayed in the target projection, but it should not crash.

I suggest to catch the error to avoid a complete crash and to remove the artist from the axis to avoid a crash at each draw().

The code below catch the error and remove the artist.
There are three ways of catching the error:

1. • plotting the grid, catching the error and removing the artist if error
2. • plotting the grid, catching the error and removing the artist then plotting each cell of the grid, catching the error for each cell and removing the artist of the cells crashing
3. • same as above plus removing the the big cells that overlap the plot.

In the following plots the bottom plots are in the data projection and they don't crash.
The top plots are in LambertAzimuthalEqualArea only the last 3 experience a crash.
Those crashes have been managed as explained above.

1. It removes the crashing artist but the other artists are still there.
2. A big cell overlap the plot thus the display is not correct.
3. The display corresponds to what is expected.

By plotting each cell, 2. and 3. will probably be far too slow for these solutions to be acceptable.

At least in a first step I suggest to implement the solution 1 to geoaxes.

The code to reproduce:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib
import cartopy.crs as ccrs


proj = ccrs.LambertAzimuthalEqualArea

lats = np.linspace(10, 42, 3)
lonsok = np.linspace(-175, -90, 2)
lonsno = np.linspace(-176, -90, 2)
lonsok, latsok = np.meshgrid(lonsok, lats)
lonsno, latsno = np.meshgrid(lonsno, lats)
#latsokfull = np.linspace(10, 70, 10)
#lonsokfull = np.linspace(-175, 174, 20)
#lonsokfull, latsokfull = np.meshgrid(lonsokfull, latsokfull)
latsnofull = np.linspace(-90, 90, 20)
lonsnofull = np.linspace(-180, 180, 20)
lonsnofull, latsnofull = np.meshgrid(lonsnofull, latsnofull)
axproj = proj(central_latitude=-30)

xyeok = axproj.transform_points(ccrs.PlateCarree(), lonsok, latsok)
xyeno = axproj.transform_points(ccrs.PlateCarree(), lonsno, latsno)

xeok = xyeok[..., 0]
yeok = xyeok[..., 1]
xeno = xyeno[..., 0]
yeno = xyeno[..., 1]
z4 = latsok[:-1, :-1] * (1 + 0.001 * lonsok[:-1, :-1])
#z4full = latsokfull[:-1,:-1] * (1 + 0.001 * lonsokfull[:-1,:-1])
z4nofull = latsnofull[:-1, :-1] * (1 +
                     0.3 * np.sin(np.deg2rad(lonsnofull[:-1, :-1])))
fig = plt.figure(figsize=(13.1, 6.4), dpi=100)
plt.tight_layout()
fig.suptitle('LambertAzimuthalEqualArea central_latitude=-30')

ax21 = plt.subplot(2, 3, 4, projection=ccrs.PlateCarree())
ax22 = plt.subplot(2, 3, 5, projection=ccrs.PlateCarree())
#ax23 = plt.subplot(2, 4, 6, projection=ccrs.PlateCarree())
ax24 = plt.subplot(2, 3, 6, projection=ccrs.PlateCarree())
ax1 = plt.subplot(2, 6, 1, projection=axproj)
ax2 = plt.subplot(2, 6, 2, projection=axproj)
#ax3 = plt.subplot(2, 7, 3, projection=axproj)
ax4 = plt.subplot(2, 6, 3, projection=axproj)
ax5 = plt.subplot(2, 6, 4, projection=axproj)
ax6 = plt.subplot(2, 6, 5, projection=axproj)
ax7 = plt.subplot(2, 6, 6, projection=axproj)

ax21.pcolor(lonsok, latsok, z4)
ax21.set_title('pcolor data no crash (-175)\n plot in data projection')
ax22.pcolor(lonsno, latsno, -z4, cmap='cool')
ax22.set_title('pcolor data crash (-176)\n plot in data projection')
#ax23.pcolor(lonsokfull, latsokfull, z4full)
#ax23.set_title('pcolor data no crash \n plot in data projection')
ax24.pcolor(lonsnofull, latsnofull, -z4nofull, cmap='cool')
ax24.set_title('pcolor data crash \n plot in data projection')

ax1.pcolor(xeok, yeok, z4)
ax1.set_title('pcolor\ndata no crash\n coords in\naxis projection')
ax2.pcolor(lonsok, latsok, z4, transform=ccrs.PlateCarree())
ax2.set_title('pcolor\ndata no crash\n coords in\ndata projection')
#ax3.pcolor(lonsokfull, latsokfull, z4full, transform=ccrs.PlateCarree())
#ax3.set_title('pcolor\ndata no crash\n coords in\ndata projection')
ax4.pcolor(xeno, yeno, -z4, cmap='cool')
ax4.set_title('pcolor\ndata crash\n coords in axis\nprojection')






try:
    mesh = ax5.pcolor(lonsno, latsno, -z4, transform=ccrs.PlateCarree(),
                      cmap='cool')
except ValueError as err:
    print('Exception ValueError', err)
    for child in ax5.get_children():
        if isinstance(child, matplotlib.collections.PolyCollection):
            child.remove()
            #del child
            print("Crashing artist removed")

# a way to plot the non crashing cells
# not managing the wrapping cells

meshcollection = []
nr, nc = lonsnofull.shape
vmin = np.nanmin(-z4nofull)
vmax = np.nanmax(-z4nofull)
for row in range(nr-1):
    for col in range(nc-1):
        try:
            mesh = ax6.pcolor(
                lonsnofull[row:row+2, col:col+2],
                latsnofull[row:row+2, col:col+2],
                -z4nofull[row:row+1, col:col+1],
                vmin=vmin,
                vmax=vmax,
                cmap='cool',
                transform=ccrs.PlateCarree())
            for child in ax6.get_children():
                if isinstance(child, matplotlib.collections.PolyCollection):
                    child.remove()
                    meshcollection.append(child)
        except ValueError as err:
            print('Exception ValueError', err)
            for child in ax6.get_children():
                if isinstance(child, matplotlib.collections.PolyCollection):
                    child.remove()
                    print("axe6 Crashing artist removed:\n",
                          lonsnofull[row, col],
                          latsnofull[row, col])
                    print(child.get_paths())
                    try:
                        path2plot = child.get_transform().transform_path(child.get_paths()[0])
                    except ValueError as err:
                        print('Path transformation exception ValueError', err)
                    # trying point transformation
#                    poly = child.get_paths()[0].to_polygons()[0]
#                    trpoly=[]
#                    tr = child.get_transform()
#                    for p in poly:
#                        trpoly.append(tr.transform_point(p))
#                    ntrpoly=np.array(trpoly)
#                    trxi=ntrpoly[...,0]
#                    tryi=ntrpoly[...,1]
#                    plt.plot(trxi, tryi,'r-', clip_on=False,
#                             transform=matplotlib.transforms.IdentityTransform())
for artist in meshcollection:
    ax6.add_artist(artist)

meshcollection = []
nr, nc = lonsnofull.shape
ax7.set_global()
dx7 = ax7.bbox.bounds[2]/2
for row in range(nr-1):
    for col in range(nc-1):
        try:
            mesh = ax7.pcolor(
                lonsnofull[row:row+2, col:col+2],
                latsnofull[row:row+2, col:col+2],
                -z4nofull[row:row+1, col:col+1],
                cmap='cool',
                vmin=vmin,
                vmax=vmax,
                transform=ccrs.PlateCarree())
            for child in ax7.get_children():
                if isinstance(child, matplotlib.collections.PolyCollection):
                    child.remove()
                    # check size and keep only artist smaller than half the
                    # projection extent in x
                    for path in child.get_paths():
                        trpath = child.get_transform().transform_path(path)
                        bbox = trpath.get_extents()
                        edge = np.hypot(*bbox.bounds[2:4])
                        if edge < dx7:
                            meshcollection.append(child)
                        else:
                            print('Big cell removed',
                                  lonsnofull[row, col],
                                  latsnofull[row, col])
        except ValueError as err:
            print('Exception ValueError', err)
            for child in ax7.get_children():
                if isinstance(child, matplotlib.collections.PolyCollection):
                    child.remove()
                    print("Crashing artist removed",
                          lonsnofull[row, col],
                          latsnofull[row, col])
for artist in meshcollection:
    ax7.add_artist(artist)

for ax in [ax21, ax24, ax1, ax2, ax6, ax7]:
    ax.set_global()
    ax.coastlines(linewidth=0.2)
    if not ax in [ax24, ax6, ax7]:
        ax.scatter(
            np.mean(np.array([lonsok[:-1, :-1], lonsok[1:, 1:]]), axis=0),
            np.mean(np.array([latsok[:-1, :-1], latsok[1:, 1:]]), axis=0),
            50, z4, edgecolors='black',
            transform=ccrs.PlateCarree())

for ax in [ax22, ax4, ax5]:
    ax.set_global()
    ax.coastlines(linewidth=0.2)
    ax.scatter(
        np.mean(np.array([lonsno[:-1, :-1], lonsno[1:, 1:]]), axis=0),
        np.mean(np.array([latsno[:-1, :-1], latsno[1:, 1:]]), axis=0),
        50, -z4, edgecolors='black', cmap='cool',
        transform=ccrs.PlateCarree())


ax5.set_title('pcolor\ndata crash\n coords in data\nprojection\n raises a ValueError')
ax6.set_title('pcolor\ndata crash\n coords in data proj\n raises a ValueError\n'
              'crashing artists\nremoved')
ax7.set_title('pcolor data crash\n coords in data proj\n raises ValueError\n'
              'crashing artists\nand big cells removed')

plt.savefig("img/small_crash_pcolor_caught.png",
            dpi=100, pad_inches=0)