Input geometry has unknown (0) SRID

Question

In the below post I make some queries and it works fine. However when I add the lines that do the coordinates conversion and the line that query the geom I receive the following error when I run the web-service:

Input geometry has unknown (0) SRID

I am new to Postgis. How can I fix this issue?

Code:

query = """  WITH data AS (
        SELECT '{featuresArray}'::json AS featuresCollection
        )
        SELECT gid,geom,type::text,properties::text,
        array_to_string(array_agg(x_4326||' '||y_4326 ORDER BY gid),',') AS g4326,
        array_to_string(array_agg(x_25832||' '||y_25832 ORDER BY gid),',') AS g25832             
        FROM (
        SELECT
        ROW_NUMBER() OVER () AS gid,
        ST_AsText(ST_GeomFromGeoJSON(feature->>'geometry')) AS geom,
        feature->>'type' AS type,
        feature->>'properties' AS properties,
        ST_X((ST_DumpPoints((ST_GeomFromGeoJSON(feature->>'geometry')))).geom) x_4326,       
        ST_Y((ST_DumpPoints((ST_GeomFromGeoJSON(feature->>'geometry')))).geom) y_4326,  
        ST_X((ST_DumpPoints((ST_Transform(ST_GeomFromGeoJSON(feature->>'geometry'),25832)))).geom) x_25832,       
        ST_X((ST_DumpPoints((ST_Transform(ST_GeomFromGeoJSON(feature->>'geometry'),25832)))).geom) y_25832

        FROM (SELECT json_array_elements(featuresCollection->'features') AS feature FROM data) AS f) j
        GROUP BY gid,type::text,properties::text,geom
        ORDER BY gid;""".format(featuresArray=featuresArray)

user_2275388 · Answer

Some PostGIS functions rely on SRS, such as ST_Transform. You have to specify which SRS you're transforming from, otherwise the conversion script has no reference to compute the new coordinates, e.g. from EPSG:25832 to EPSG:4326:

SELECT ST_Transform('SRID=25832;POINT(1 1)',4326);

.. otherwise it will raise an exception

SELECT ST_Transform('POINT(1 1)',4326); -- <-- WKT literal without SRS
ERROR:  ST_Transform: Input geometry has unknown (0) SRID

With ST_SetSRID you can set the SRS to geometries in case they haven't any - as your example suggests, e.g. .

SELECT ST_Transform(
         ST_SetSRID('POINT(1 1)'::geometry,25832),
         4326);

The same principle goes for CREATE TABLE and INSERT / UPDATE statements. When creating a table we declare the SRS as follows ..

CREATE TABLE t (geom geometry(point,4326));

.. so PostGIS expects that all incoming geometries have the same SRS ..

INSERT INTO t VALUES ('SRID=4326;POINT(1 1)');

.. otherwise it raises an exception too

INSERT INTO t VALUES ('SRID=25832;POINT(1 1)'); 
ERROR:  Geometry SRID (25832) does not match column SRID (4326)

Input geometry has unknown (0) SRID

1 Answers