No Shapely geometry can be created from null value

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

[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.