No Shapely geometry can be created from null value

[gnthibault]

Expected behavior and actual behavior.

Expected behaviour: no error
Actual behaviour:

TopologyException: assigned depths do not match at 882.50000000000011 1241.5
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-69-fe56313cbba3> in <module>
----> 1 line.parallel_offset(distance=2.5, side='left')

~/anaconda3/lib/python3.6/site-packages/shapely/geometry/linestring.py in parallel_offset(self, distance, side, resolution, join_style, mitre_limit)
    144         try:
    145             return geom_factory(self.impl['parallel_offset'](
--> 146                 self, distance, resolution, join_style, mitre_limit, side))
    147         except OSError:
    148             raise TopologicalError()

~/anaconda3/lib/python3.6/site-packages/shapely/geometry/base.py in geom_factory(g, parent)
     74     # Abstract geometry factory for use with topological methods below
     75     if not g:
---> 76         raise ValueError("No Shapely geometry can be created from null value")
     77     ob = BaseGeometry()
     78     geom_type = geometry_type_name(g)

ValueError: No Shapely geometry can be created from null value

Steps to reproduce the problem.

import shapely
line = shapely.geometry.linestring.LineString([(884.0, 1240.0),(883.0, 1239.0),(882.0, 1239.0),(881.0, 1240.0)])                                                                                   
line.parallel_offset(distance=2.5, side='left') 

The weird thing is that the problem does not show if distance=2.499999999999 or distance=2.5000000000001

Operating system

Distributor ID: Ubuntu
Description: Ubuntu 16.04.6 LTS
Release: 16.04
Codename: xenial

Shapely version and provenance

Shapely==1.6.4.post2 installed from PyPI using pip

[sgillies]

@gnthibault would you be willing to try to reproduce the problem using shapely==1.7a3 and shapely==1.7b1? I have a feeling this is an upstream bug that has been fixed.

[Jeremiah-England]

I can reproduce this with python 3.8.2, shapely==1.7.1 on a WSL using Ubuntu 20.04.1,

from shapely.geometry import LineString
line = LineString([(884.0, 1240.0),(883.0, 1239.0),(882.0, 1239.0),(881.0, 1240.0)])
print(line.parallel_offset(distance=2.5, side='left').wkt)

TopologyException: assigned depths do not match at 882.50000000000011 1241.5
Traceback (most recent call last):
  File "shapely_890.py", line 3, in <module>
    print(line.parallel_offset(distance=2.5, side='left').to_wkt())
  File "/home/jengland/.local/lib/python3.8/site-packages/shapely/geometry/linestring.py", line 145, in parallel_offset
    return geom_factory(self.impl['parallel_offset'](
  File "/home/jengland/.local/lib/python3.8/site-packages/shapely/geometry/base.py", line 78, in geom_factory
    raise ValueError("No Shapely geometry can be created from null value")
ValueError: No Shapely geometry can be created from null value

It does not happen for 2.5000000000001, but it does for 2.50000000000001.

[Jeremiah-England]

I ran into another example of this issue, only it has a different topology exception underneath:

import shapely.wkt
shapely.wkt.loads('LINESTRING (12 20, 60 68, 111 114, 151 159, 210 218)').parallel_offset(3)

TopologyException: found non-noded intersection between LINESTRING (25.1837 28.941, 25.1837 28.941) and LINESTRING (25.1837 28.941, 25.1837 28.941) at 25.183658239422783 28.941017552303521

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-21-df893580dce5> in <module>
----> 1 shapely.wkt.loads('LINESTRING (12 20, 60 68, 111 114, 151 159, 210 218)').parallel_offset(3)

~/.local/lib/python3.8/site-packages/shapely/geometry/linestring.py in parallel_offset(self, distance, side, resolution, join_style, mitre_limit)
    143                 'Cannot compute offset from zero-length line segment')
    144         try:
--> 145             return geom_factory(self.impl['parallel_offset'](
    146                 self, distance, resolution, join_style, mitre_limit, side))
    147         except OSError:

~/.local/lib/python3.8/site-packages/shapely/geometry/base.py in geom_factory(g, parent)
     76     # Abstract geometry factory for use with topological methods below
     77     if not g:
---> 78         raise ValueError("No Shapely geometry can be created from null value")
     79     ob = BaseGeometry()
     80     geom_type = geometry_type_name(g)

ValueError: No Shapely geometry can be created from null value

---

This is a different issue in GEOS than the one @gnthibault found. I can mine more of them with the following script pretty easily:

Script

# took my machine about 7 minutes to run
from shapely.geometry import LineString
import random

for _ in range(100000):
    x = [i*20 + random.randint(0, 10) for i in range(5)]
    y = [i*20 + random.randint(0, 10) for i in range(5)]
    ls = LineString(zip(x, y))
    try:
        for d in range(10):
            ls.parallel_offset(d)
    except:
        print(ls.wkt)
        print(d)

Out of 100,000 LineStrings, I got 7 of these topology exceptions. However, I got none of OP's.

It appears that OP's has been reported in the geos tracker here: https://trac.osgeo.org/geos/ticket/682 (another assigned depths do not match... error). But I couldn't find any OffsetCurve tickets that referenced a found non-noded intersection error.

[jorisvandenbossche]

With latest main branch, we correctly raise the GEOS error instead of the confusing "No Shapely geometry can be created from null value" error:

>>> from shapely.geometry import LineString
>>> line = LineString([(884.0, 1240.0),(883.0, 1239.0),(882.0, 1239.0),(881.0, 1240.0)])
>>> line.parallel_offset(distance=2.5, side='left')
...
GEOSException: TopologyException: assigned depths do not match at 882.50000000000011 1241.5

So I think we label / close this as an upstream GEOS issue?

[jorisvandenbossche]

In addition, with GEOS 3.11, this now works without exception:

>>> from shapely.geometry import LineString
>>> line = LineString([(884.0, 1240.0),(883.0, 1239.0),(882.0, 1239.0),(881.0, 1240.0)])
>>> line.parallel_offset(distance=2.5, side='left')
<LINESTRING (885.768 1238.232, 884.768 1237.232, 884.586 1237.067, 884.389 1...>

GEOS 3.11 will be included in the shapely 2.0 wheels (and with conda you also already use this with shapely 1.8.5).

Closing as fixed upstream in GEOS.