CODEWITHSUNDEEP
gispostgisutm
Esteban S
Esteban S

Reputation: 1919

Convert from EPSG:4326 to UTM in PostGIS

I would like to convert from EPSG:4326 to UTM (30N/EPSG:32630 or 29N/EPSG:32629) in PostGIS. I do the following query but I get wrong results:

SELECT ST_AsText(ST_Transform(ST_GeomFromText('POINT(36.5277099609375 -5.86424016952515)',4326),32630)) As check;

I get "POINT(5262418.33128724 -839958.963432011)" when it should be something approximate to 243625.00,4046330.00 in UTM 30N. If I do the conversion from 4326 to UTM I get the right result but not from UTM to 4326.

Upvotes: 5

Views: 7594

Answers (3)

Esteban S
Esteban S

Reputation: 1919

The reason is because is not POINT(36.5277099609375 -5.86424016952515), but POINT(-5.86424016952515 36.5277099609375)because longitude and latitude depends on the system. Normally X=longitude and Y=latitude, but e.g. in Google Maps X is the lat and Y is the long.

Upvotes: 0

Tom-db
Tom-db

Reputation: 6868

1) Your query is correct but you coordinates are inverted. The correct coordinates order in the WKT format is POINT(x y), also POINT(longitude latitude)

This query give you the expected result:

SELECT ST_AsText(ST_Transform(ST_GeomFromText('POINT(-5.86424016952515 36.5277099609375)',4326),32630)) As check;

2) To get the UTM zone from a lat/long geometry you can use this formula:

ST_X(input_geometry)+180)/6)+1

with some adjustments.

For this purpose we use this function:

CREATE OR REPLACE FUNCTION get_utmzone(input_geom geometry)
  RETURNS integer AS
$BODY$
DECLARE
   zone int;
   pref int;
BEGIN
   IF GeometryType(input_geom) != 'POINT' THEN
     RAISE EXCEPTION 'Input geom must be a point. Currently is: %', GeometryType(input_geom);
   END IF;
   IF ST_Y(input_geom) >0 THEN
      pref:=32600;
   ELSE
      pref:=32700;
   END IF;
   zone = floor((ST_X(input_geom)+180)/6)+1;
   RETURN zone+pref;
END;
$BODY$
LANGUAGE plpgsql IMMUTABLE;

Use it with this query:

SELECT get_utmzone(ST_GeomFromText('POINT( -5.86424016952515 36.5277099609375)',4326));

The result should be 32630

Upvotes: 10

Jendrusk
Jendrusk

Reputation: 813

Firs thing is that following documentation of OpenGIS WKT Point(x,y) yours POINT(36.5277099609375 -5.86424016952515) is south of equator so you have to use 29S(EPSG:32729) and 30S(EPSG:32730)

Upvotes: 1

Related Questions