Setting CRS of point using shapely

Question

I am working on a tool, which transfers data, including geometries, from different legacy databases to postgis.

Currently this means I have a MS-access Database, which contains point geometries, but since access does not have a geometry type, the points consist of two columns, containing numbers, like so:

lat	lon
371744,668	5700069,115

During the flow of my tool, I take these coordinates with pyodbc, and use shapely to create a point. This point does not have crs since it is newly created. Now I'm trying to set it to EPSG:25832, since the postgis DB expects geometry data to be in 25832. The code below shows what is going on. In the docs I found an example, and even when I'm directly pasting the example to my code it does not work.

What am I missing here?

def getGeomAsWKB(self, table, ids):
    tmp = self.getCoordinates(table) # tmp = list of tuples with coordinate pairs [(X,Y),(X2,Y2)...]
    geoms = []
    for coords in tmp:
        pt = Point(coords) no crs at this point, as to be expected
        srid = pyproj.CRS('EPSG:25832')
        old_srid = pyproj.CRS('EPSG:25832')
        project = pyproj.Transformer.from_crs(old_srid, srid, always_xy=True).transform
        t_pt = transform(project, pt) nothing changes
        #pt._crs = 'EPSG:25832'# i tried to set it this way, becausei did not know what else to try
        tmp_binary = wkb.dumps(t_pt)
        geoms.append(tmp_binary)
    return geoms

Just to be clear, pt and t_pt are correctly build, its just that t_pt does not contain the crs information after the transformation.

Postgis return the following error code :

Geometry SRID (0) does not match column SRID (25832)

Answer 1

Shapely geometries are unaware of their CRS. Using pyproj to transform them only changes the values of the coordinates without leaving any trace of the final CRS in the resulting geometries. Serializing a shapely geometry to wkb will never write the CRS information.

However, one option I am aware of is using GeoPandas to set the CRS and write to a file format which supports CRS information (i.e. not geojson). Some links to related methods in the geopandas docs:

• GeoDataFrame.set_crs
• GeoDataFrame.to_crs
• I have never used it, but it looks like there is a way to write a GeoDataFrame directly to a PostGIS database. Otherwise, you might try writing to one of the many file formats which support CRS information using the GeoDataFrame.to_file method.

It looks like shapely.wkb.dumps supports an optional srid argument which is missing from the documentation!