使用逆函数将几何转换为坐标会导致混合SRID错误

Question

I'm using postgres with postig extension. I have coordinates which I put into following postgis function:

select ST_SetSRID(ST_point(18.533935546875, 48.23199134320962),4674) 

As a result, I get geometry type: 01010000204212000000000000B08832402D0570E4B11D4840

When I want to do inverse action

select st_x(st_transform(way,4326)), st_y(st_transform(way,4326)) from planet_osm_point where way ='01010000204212000000000000B08832402D0570E4B11D4840'

I get error:

ERROR:  Operation on mixed SRID geometries
********** Error **********
ERROR: Operation on mixed SRID geometries
SQL state: XX000

What can be the problem?

Answer 1

The problem is somewhat described in the error message: you are trying to find equal geometries in planet_osm_point.way , but they have a different SRID than 4674. It is effectively this:

SELECT ST_SetSRID(ST_Point(0, 0), 4674) = ST_SetSRID(ST_Point(0, 0), 4326);

So you would need to pick a common SRID, and transform one to the other, ie

SELECT ST_SetSRID(ST_Point(0, 0), 4674) =
                      ST_Transform(ST_SetSRID(ST_Point(0, 0), 4326), 4674);

except I don't recommend using the =(geometry, geometry) operator since it requires identical geometries, which are not very common with floating point errors after transforming.

A better approach is to find all the way geometries within a small margin of error distance using ST_DWithin :

select st_x(st_transform(way,4326)), st_y(st_transform(way,4326))
from planet_osm_point
where ST_DWithin(
         way,
         ST_Transform(
           ST_SetSRID(ST_Point(18.533935546875, 48.23199134320962), 4674),
           <way_SRID>),
         1e-6);

Here, it transforms the point into the SRID of way (you never specified, so update <way_SRID> ), then find anything within 1e-6 degrees distance away (about 10 cm). Increase it if you want to collect more nearby way points.