[Matplotlib-users] tricontour crashing in QGIS3

[Benjamin Root]

Looks like a conflict for the qhull library, which matplotlib vendors and
builds as a part of its packaging. How did qgis and matplotlib get
installed? Perhaps they were built with conflicting flags, perhaps? Just a
few ideas off of the top of my head.

Ben Root


On Sun, Feb 4, 2018 at 3:55 PM, Chris Crook <ccrook at linz.govt.nz> wrote:

> I'm looking for help debugging or fixing a problem in matplotlib
> tricontour.  I am using this in a QGIS plugin (www.qgis.org).  The call
> to tricontour causes QGIS to crash.   Running python3 on ubuntu 16.04
> (matplotlib 1.5.1) and 17.10 (matplotlib 2.0.0).
>
> Running in the debugger gives the following result
>
> Thread 1 "qgis.bin" received signal SIGSEGV, Segmentation fault.
> 0x00007fff4f7ca098 in qh_initstatistics ()
>    from /usr/lib/python3/dist-packages/matplotlib/_qhull.
> cpython-35m-x86_64-linux-gnu.so
> #0  0x00007fff4f7ca098 in qh_initstatistics ()
>    from /usr/lib/python3/dist-packages/matplotlib/_qhull.
> cpython-35m-x86_64-linux-gnu.so
> #1  0x00007fff4f7c6f82 in qh_initqhull_start ()
>    from /usr/lib/python3/dist-packages/matplotlib/_qhull.
> cpython-35m-x86_64-linux-gnu.so
> #2  0x00007fff4f7d12bc in qh_new_qhull ()
>    from /usr/lib/python3/dist-packages/matplotlib/_qhull.
> cpython-35m-x86_64-linux-gnu.so
> #3  0x00007fff4f7a3821 in ?? ()
>    from /usr/lib/python3/dist-packages/matplotlib/_qhull.
> cpython-35m-x86_64-linux-gnu.so
> #4  0x00007fff5d977039 in PyCFunction_Call ()
>    from /usr/lib/x86_64-linux-gnu/libpython3.5m.so.1.0
> #5  0x00007fff5da831b5 in PyEval_EvalFrameEx ()
>    from /usr/lib/x86_64-linux-gnu/libpython3.5m.so.1.0
> #6  0x00007fff5db13cac in ?? ()
>    from /usr/lib/x86_64-linux-gnu/libpython3.5m.so.1.0
> #7  0x00007fff5db13d83 in PyEval_EvalCodeEx ()
>    from /usr/lib/x86_64-linux-gnu/libpython3.5m.so.1.0
> #8  0x00007fff5d99bad8 in ?? ()
>    from /usr/lib/x86_64-linux-gnu/libpython3.5m.so.1.0
> ....
>
> The python code is
>
>                 np.save('/home/chris/temp/data.x',x)
>                 np.save('/home/chris/temp/data.y',y)
>                 np.save('/home/chris/temp/data.z',z)
>                 np.save('/home/chris/temp/data.l',levels)
>                 print("Extend",repr(extend))
>                 cs = plt.tricontour(x, y, z, levels, extend=extend)
>
> I've called matplotlib from a simple python script using the saved data
> (np.save) in a simply python script and it runs without problem, so the
> problem appears to arise running within the QGIS3 python environment.
>
> Can you suggest any reason why it might be different running from within
> QGIS and how I can work around/fix this!
>
> Thanks
> Chris Crook
>
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