Getting geometry from attribute using PyQGIS

Question

I am using PyQGIS 3.

I pull in a line table from postgres database. and one of the attributes is a point geometry, when I open the attribute table that column shows data in this format: SRID=4326;POINT(-101.82683089226423 31.232703471526868)

and printing out this attribute for each feature prints this out as a string. Printing out the type name and type I get this:

TypeName:geometry, Type:10

How do I deal with this in my python code?

Do I have to treat it like a string and split the text to get the "POINT(-101.82683089226423 31.232703471526868)" or is there a way to treat this as a point geometry so that I can do QgsGeometry things with it?

I tried this:
print(QgsGeometry.fromWkt(feature['label_location']))
and I got this:
<QgsGeometry: null>

How do I cast this to a QgsGeometry?

This works:

QgsGeometry.fromWkt(feature['label_location'].split(';')[-1])

but seems kind of crude.

Is there a better way?

I tried to use the above method to update the attribute, but I could not update it in a way that maintains the format. I have another place in my code that expects this specific string format and in the postgres table it is wkb. I would like to avoid running a query to do this and would ideally find a way to use all QGIS functions but it may not be possible.

Answer 1

This format is known as EWKT (Extended Well-Known text, see https://postgis.net/docs/ST_GeomFromEWKT.html) and currently not supported in QGIS except for certain PostGIS contexts.

You can see their implementation at https://github.com/qgis/QGIS/blob/46a2458cdf50364442b009cbb3fcee61eccdd835/src/providers/postgres/qgspostgresprovider.cpp#L417 and borrow the regular expression if you prefer it to the split() approach. I think your approach is pretty much perfect.

This might make a great feature request in QGIS. See https://lists.osgeo.org/pipermail/qgis-developer/2022-January/064394.html for some existing discussion around it.

Answer 2

You use the geometry() method of the feature to get the point (or line, or polygon).

for f in features:
    geom = f.geometry()