GeoAlchemy and SQLAlchemy thoughts

I’m doing a new geo-project, a GPS tracker sort of thing. My database is very simple, just a Users table and a Locations table holding points. But I figured I’d front-load the work and use SQLAlchemy and Alembic and PostGIS and everything right now, not pay the pain of migrating later when I realize I need the fancier stuff.

Only SQLAlchemy doesn’t support PostGIS. GeoAlchemy2 does though. After an hour with it I can’t decide if it’s good or bad. It seems very simple.

In GeoAlchemy2 all geodata is represented in Python by just a few types; Geometry, Geography, Raster. You can’t do much with those things other than get the WKB or WKT for them. They’re not Points or Polygons or something, there’s no Python code for working with the shapes. You can pass them back to PostGIS though, to call functions like ST_Area to have PostGIS do a calculation. Requires a database round trip though. Alternately you can also convert them to Shapely shapes, use that excellent GIS library to do work in Python.

I guess that’s a reasonable compromise; GeoAlchemy2 is really just bridging to SQL, they’re not going to implement their own GEOS equivalent. It also has spatial functions declared in a SQLAlchemy-friendly way you so you can use SQLAlchemy syntax to do your work. That’s kinda neat.

Still I’m looking at a lot of third party Python code: SQLAlchemy, Shapely, GeoAlchemy, Alembic. All to manage a database with two tables and nothing more complex than a list of points. I may blow it all off and go to raw SQL. OTOH I may end up regretting that choice in a few months if I want to do more complex things.


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