PostGIS Spatial Queries & ST_Transform Coordinate Reference Guide
Essential PostGIS Functions
ST_Transform(geom, target_srid)— Reproject geometry coordinates dynamically across EPSG reference systems.ST_SetSRID(geom, srid)— Assign a Spatial Reference ID without altering underlying vertex numerical values.ST_Distance(geom1, geom2)— Calculate Euclidean planar distance (in units of CRS, e.g. meters for UTM, degrees for WGS84).
1. Reprojecting Geometries with ST_Transform
SELECT id, name,
ST_AsGeoJSON(ST_Transform(geom, 4326)) AS geojson_wgs84
FROM spatial_table
WHERE ST_DWithin(ST_Transform(geom, 32654), ST_MakePoint(395000, 3950000), 5000);
ST_AsGeoJSON(ST_Transform(geom, 4326)) AS geojson_wgs84
FROM spatial_table
WHERE ST_DWithin(ST_Transform(geom, 32654), ST_MakePoint(395000, 3950000), 5000);