How do I create an emptry LineString in GeoDjango

Question

I am having a problem with the latest version of the GeoDjango extensions in Django version 4.2.6 when I create an empty LineString. The same code is behaving differently than it did in version 4.0.10. The default seems to have switched to creating a Geos object with 3-dimensions rather than the previous 2-dimensions.

The following code returns a different WKT object depending on the version of Django I am using.

from django.contrib.gis.geos import LineString
ls = LineString()
ls.wkt

This is returning a 3-dimensional object "LINESTRING Z EMPTY". Running exactly the same code on Django 4.0.10 creates a 2-dimension object "LINESTRING EMPTY".

Is there anything obvious I am doing wrong? I am also running a slightly newer version of geos-3.12.0 versus 3.11.2 but I cannot see anything is both sets of release notes that describe this change in behaviour.

Answer 1

This issue turned out to be due to a change in the way geos handles empty LineString objects. This has now been corrected in a patch to the master branch. See https://github.com/libgeos/geos/issues/993 for the details of the issue and the patch that fixes it.

Answer 2

In GeoDjango,starting from version 3.1, 3D geometries are supported by default. If you want to create a 2D LineString explicitly, you can use the dim parameter when creating the LineString object. Set dim=2 to create a 2D LineString.

from django.contrib.gis.geos import LineString
ls = LineString(dim=2)
print(ls.wkt)