I tried to create a polygon shapefile in QGIS and read it in python by shapely. An example code looks like this:
import fiona
from shapely.geometry import shape
multipolys = fiona.open(somepath)
multi = multipolys[0]
coord = shape(multi['geometry'])
The EOSGeom_createLinearRing_r returned a NULL pointer I checked if the polygon is valid in QGIS and no error was reported. Actually, it does not work for even a simple triangle generated in QGIS. Anyone knows how to solve it?
Thank you
Like J. P., I had this issue with creating LineStrings as well. There is an old issue (2016) in the Shapely github repository that seems related. Changing the order of the imports solved the problem for me:
from shapely.geometry import LineString
import fiona
LineString([[0, 0], [1, 1]]).to_wkt()
# 'LINESTRING (0.0000000000000000 0.0000000000000000, 1.0000000000000000 1.0000000000000000)'
whereas
import fiona
from shapely.geometry import LineString
LineString([[0, 0], [1, 1]]).to_wkt()
# Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# File "C:\Users\xxxxxxx\AppData\Roaming\Python\Python37\site-packages\shapely\geometry\linestring.py", line 48, in __init__
# self._set_coords(coordinates)
# File "C:\Users\xxxxxxx\AppData\Roaming\Python\Python37\site-packages\shapely\geometry\linestring.py", line 97, in _set_coords
# ret = geos_linestring_from_py(coordinates)
# File "shapely\speedups\_speedups.pyx", line 208, in shapely.speedups._speedups.geos_linestring_from_py
# ValueError: GEOSGeom_createLineString_r returned a NULL pointer
Some other issues in the Shapely repository to look at
I had a similar problem but with the shapely.geometry.LineString. The error I got was
ValueError: GEOSGeom_createLineString_r returned a NULL pointer
I don't know the reason behind this message, but there are two ways, how to avoid it:
Do the following:
...
from shapely import speedups
...
speedups.disable()
Import the speedups module and disable the speedups. This needs to be done, since they are enabled by default. From shapelys speedups init method:
"""
The shapely.speedups module contains performance enhancements written in C.
They are automaticaly installed when Python has access to a compiler and
GEOS development headers during installation, and are enabled by default.
"""
If you disable them, you won't get the NULL Pointer Exception, because you don't use the C implementation, rather than the usual implementation.
If you call python in a command shell, type:
from shapely.geometry import shape
this loads your needed shape. Then load your program
import yourscript
then run your script.
yourscript.main()
This should also work. I think in this variant the C modules get properly loaded and therefore you don't get the NULL Pointer Exception. But this only works, if you open a python terminal by hand and import the needed shape by hand. If you import the shape with your program, you will run into the same error again.