triplot IndexError when lost marker and linestyle paraments

[purpleskyfall]

Description

In my case, using plt.triplot() function when lost marker and linestyle paraments will cause an error.

Code to reproduce

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

xy = np.asarray([
    [-0.101, 0.872], [-0.080, 0.883], [-0.069, 0.888], [-0.054, 0.890],
    [-0.045, 0.897], [-0.057, 0.895], [-0.073, 0.900], [-0.087, 0.898],
    [-0.090, 0.904], [-0.069, 0.907], [-0.069, 0.921], [-0.080, 0.919],
    [-0.073, 0.928], [-0.052, 0.930], [-0.048, 0.942], [-0.062, 0.949],
    [-0.054, 0.958], [-0.069, 0.954], [-0.087, 0.952], [-0.087, 0.959],
    [-0.080, 0.966], [-0.085, 0.973], [-0.087, 0.965], [-0.097, 0.965],
    [-0.097, 0.975], [-0.092, 0.984], [-0.101, 0.980], [-0.108, 0.980],
    [-0.104, 0.987], [-0.102, 0.993], [-0.115, 1.001], [-0.099, 0.996],
    [-0.101, 1.007], [-0.090, 1.010], [-0.087, 1.021], [-0.069, 1.021],
    [-0.052, 1.022], [-0.052, 1.017], [-0.069, 1.010], [-0.064, 1.005],
    [-0.048, 1.005], [-0.031, 1.005], [-0.031, 0.996], [-0.040, 0.987],
    [-0.045, 0.980], [-0.052, 0.975], [-0.040, 0.973], [-0.026, 0.968],
    [-0.020, 0.954], [-0.006, 0.947], [ 0.003, 0.935], [ 0.006, 0.926],
    [ 0.005, 0.921], [ 0.022, 0.923], [ 0.033, 0.912], [ 0.029, 0.905],
    [ 0.017, 0.900], [ 0.012, 0.895], [ 0.027, 0.893], [ 0.019, 0.886],
    [ 0.001, 0.883], [-0.012, 0.884], [-0.029, 0.883], [-0.038, 0.879],
    [-0.057, 0.881], [-0.062, 0.876], [-0.078, 0.876], [-0.087, 0.872],
    [-0.030, 0.907], [-0.007, 0.905], [-0.057, 0.916], [-0.025, 0.933],
    [-0.077, 0.990], [-0.059, 0.993]])

x = np.degrees(xy[:, 0])
y = np.degrees(xy[:, 1])

triangles = np.asarray([
    [67, 66,  1], [65,  2, 66], [ 1, 66,  2], [64,  2, 65], [63,  3, 64],
    [60, 59, 57], [ 2, 64,  3], [ 3, 63,  4], [ 0, 67,  1], [62,  4, 63],
    [57, 59, 56], [59, 58, 56], [61, 60, 69], [57, 69, 60], [ 4, 62, 68],
    [ 6,  5,  9], [61, 68, 62], [69, 68, 61], [ 9,  5, 70], [ 6,  8,  7],
    [ 4, 70,  5], [ 8,  6,  9], [56, 69, 57], [69, 56, 52], [70, 10,  9],
    [54, 53, 55], [56, 55, 53], [68, 70,  4], [52, 56, 53], [11, 10, 12],
    [69, 71, 68], [68, 13, 70], [10, 70, 13], [51, 50, 52], [13, 68, 71],
    [52, 71, 69], [12, 10, 13], [71, 52, 50], [71, 14, 13], [50, 49, 71],
    [49, 48, 71], [14, 16, 15], [14, 71, 48], [17, 19, 18], [17, 20, 19],
    [48, 16, 14], [48, 47, 16], [47, 46, 16], [16, 46, 45], [23, 22, 24],
    [21, 24, 22], [17, 16, 45], [20, 17, 45], [21, 25, 24], [27, 26, 28],
    [20, 72, 21], [25, 21, 72], [45, 72, 20], [25, 28, 26], [44, 73, 45],
    [72, 45, 73], [28, 25, 29], [29, 25, 31], [43, 73, 44], [73, 43, 40],
    [72, 73, 39], [72, 31, 25], [42, 40, 43], [31, 30, 29], [39, 73, 40],
    [42, 41, 40], [72, 33, 31], [32, 31, 33], [39, 38, 72], [33, 72, 38],
    [33, 38, 34], [37, 35, 38], [34, 38, 35], [35, 37, 36]])

fig = plt.figure(figsize=[8, 16])
ax = plt.axes(projection=ccrs.OSGB())
ax.add_feature(cfeature.OCEAN.with_scale('50m'))
ax.add_feature(cfeature.LAND.with_scale('50m'))
ax.gridlines(linestyle='--')
# plt.triplot(x, y, triangles, transform=ccrs.Geodetic(), marker='o', linestyle='-')
plt.triplot(x, y, triangles, transform=ccrs.Geodetic())
plt.show()

will case:

Traceback

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\IPython\core\formatters.py in __call__(self, obj)
    339                 pass
    340             else:
--> 341                 return printer(obj)
    342             # Finally look for special method names
    343             method = get_real_method(obj, self.print_method)

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\IPython\core\pylabtools.py in <lambda>(fig)
    239 
    240     if 'png' in formats:
--> 241         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
    242     if 'retina' in formats or 'png2x' in formats:
    243         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\IPython\core\pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
    123 
    124     bytes_io = BytesIO()
--> 125     fig.canvas.print_figure(bytes_io, **kw)
    126     data = bytes_io.getvalue()
    127     if fmt == 'svg':

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\matplotlib\backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, **kwargs)
   2208                 bbox_filtered = []
   2209                 for a in bbox_artists:
-> 2210                     bbox = a.get_window_extent(renderer)
   2211                     if a.get_clip_on():
   2212                         clip_box = a.get_clip_box()

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\matplotlib\lines.py in get_window_extent(self, renderer)
    630         bbox = Bbox([[0, 0], [0, 0]])
    631         trans_data_to_xy = self.get_transform().transform
--> 632         bbox.update_from_data_xy(trans_data_to_xy(self.get_xydata()),
    633                                  ignore=True)
    634         # correct for marker size, if any

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\matplotlib\transforms.py in transform(self, values)
   1330 
   1331         # Transform the values
-> 1332         res = self.transform_affine(self.transform_non_affine(values))
   1333 
   1334         # Convert the result back to the shape of the input values.

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\matplotlib\transforms.py in transform_non_affine(self, points)
   2374             return points
   2375         elif not self._a.is_affine and self._b.is_affine:
-> 2376             return self._a.transform_non_affine(points)
   2377         else:
   2378             return self._b.transform_non_affine(

c:\users\asus\appdata\local\programs\python\python35\lib\site-packages\cartopy\mpl\geoaxes.py in transform_non_affine(self, xy)
    135         if isinstance(xy, np.ndarray):
    136             return prj.transform_points(self.source_projection,
--> 137                                         xy[:, 0], xy[:, 1])[:, 0:2]
    138         else:
    139             x, y = xy

lib\cartopy\_crs.pyx in cartopy._crs.CRS.transform_points()

IndexError: Out of bounds on buffer access (axis 0)

but when I add 2 paraments marker='o' and linestyle='-' in plt.triplot() function, it works:

plt.triplot(x, y, triangles, transform=ccrs.Geodetic(), marker='o', linestyle='-')

So, did I find a bug?

Full environment definition

Operating system

Windows 10, 1709, 64bit.

Cartopy version

CPython: 3.5.3
Cartopy: 0.16.0

pip list

Package             Version
------------------- -----------
aiofiles            0.3.1
aioftp              0.8.0
astroid             1.5.3
backcall            0.1.0
bleach              2.0.0
Cartopy             0.16.0
colorama            0.3.9
cycler              0.10.0
decorator           4.1.2
entrypoints         0.2.3
gnsscal             1.1.0
html5lib            0.999999999
ipykernel           4.6.1
ipython             6.3.1
ipython-genutils    0.2.0
ipywidgets          7.0.1
isort               4.2.15
jdcal               1.3
jedi                0.11.0
Jinja2              2.9.6
jsonschema          2.6.0
jupyter             1.0.0
jupyter-client      5.1.0
jupyter-console     5.2.0
jupyter-core        4.3.0
lazy-object-proxy   1.3.1
MarkupSafe          1.0
matplotlib          2.0.2
mccabe              0.6.1
mistune             0.7.4
mpmath              0.19
nbconvert           5.3.1
nbformat            4.4.0
notebook            5.1.0
numpy               1.14.1+mkl
pandas              0.20.3
pandocfilters       1.4.2
parso               0.1.0
pickleshare         0.7.4
Pillow              5.0.0
pip                 10.0.0
prompt-toolkit      1.0.15
Pygments            2.2.0
pylint              1.7.2
PyMySQL             0.7.11
pynmea2             1.12.0
pyparsing           2.2.0
pyproj              1.9.5.1
pyshp               1.2.12
python-dateutil     2.6.1
pytz                2017.2
PyYAML              3.12
pyzmq               16.0.2
qtconsole           4.3.1
scikit-learn        0.19.1
scipy               0.19.1
setuptools          38.5.1
Shapely             1.6.4.post1
simplegeneric       0.8.1
six                 1.11.0
sympy               1.1.1
testpath            0.3.1
tornado             4.5.2
tqdm                4.19.9
traitlets           4.3.2
wcwidth             0.1.7
webencodings        0.5.1
wheel               0.29.0
widgetsnbextension  3.0.3
win-unicode-console 0.5
wrapt               1.10.10

[dopplershift]

Hmm. This worked fine for me (without the extra arguments) on Python 3.6, matplotlib 2.2.2, cartopy 0.16.0, Shapely 1.6.4 (all from conda-forge). What about you?

[purpleskyfall]

I upgraded matplotlib from 2.0.2 to 2.2.2 from https://www.lfd.uci.edu/~gohlke/pythonlibs/#matplotlib, but it not works with Python 3.5, cartopy 0.16.0, Shapely 1.6.4.

Also, I test this on another PC with Python 3.6.3, matplotlib 2.1.0, cartopy 0.16.0 & Shapely 1.6.4 (install by anaconda), the IndexError sitll happens.

Thanks, @dopplershift

[cgohlke]

Works for me too. I can't reproduce the issue with binaries from https://www.lfd.uci.edu/~gohlke/pythonlibs

[purpleskyfall]

For me, this worked fine in Python Shell but failed in Jupyter notebook, so could you test it in Jupyter notebook? Thanks. @cgohlke @dopplershift

[cgohlke]

For me, this worked fine in Python Shell but failed in Jupyter notebook, so could you test it in Jupyter notebook?

Confirmed. I can reproduce the issue in Jupyter notebook.

[dopplershift]

I can reproduce in the notebook as well. It looks like this is caused by the fact that the notebook calls savefig() with bbox_inches='tight'. A workaround is to disable this by putting this in a cell and running it before making the plot:

%config InlineBackend.print_figure_kwargs = {'bbox_inches':None}

This at least makes it work for me. I need to dig further to understand why it fails.

[dopplershift]

Ok, so the problem is that without a marker, triplot ends up doing:

ax.plot([], [], **kw)

This yields a line with 0 points--just doing the above is enough to trigger the problem.

The code for transform_points() on CRS has one line that doesn't like this:

status = pj_transform(src_crs.proj4, self.proj4, npts, 3,
                      &result[0, 0], &result[0, 1], &result[0, 2])

(0 index on a size 0 axis is invalid). PR incoming...

[dopplershift]

See #1062.