Can someone tell me why this keeps returning degrees instead of meters?

Question

Can someone tell me why this keeps returning degrees instead of meters? I’m transforming the geometry SRID to 32613, which measures in meters. Thanks

SELECT storm_date, hail_size_inches, 
       ST_Distance(
         ST_Transform(geom32613, 32613), 
         ST_SetSRID(
           ST_MakePoint(-104.89907, 39.66643), 
           32613)
       ) distance
FROM hail.hail_swaths
WHERE storm_date >= '2021/06/01'

JGH · Answer 1 · 2021-06-17T13:10:21.437

2

You are using lat-long coordinates (4326) as if they were in 32613.

ST_SetSRID(ST_MakePoint(-104.89907, 39.66643), 32613) --> replace with ST_Transform(ST_SetSRID(ST_MakePoint(-104.89907, 39.66643), 4326),32613);

Also double check what values are stored in the column geom32613. If they are indeed in 32613, there is no need to reproject them

Example for 1 degree, near the central meridian for this projection:

SELECT ST_Distance(ST_Transform('SRID=4326;POINT(-105 40)',32613),
jgtest(>    ST_Transform('SRID=4326;POINT(-106 40)',32613));
   st_distance
------------------
 85361.8049211818

edited Jun 17 '21 at 13:10

answered Jun 16 '21 at 20:48

JGH

15,928
4
31
48

Thanks. I’m measuring the distance from a MultiPolygon to a Point. I thought this would return the distance from the Point geometry to the closest Polygon in the Multipolygon geometry. Is this an incorrect assumption? – Nick Michniok Jun 17 '21 at 21:10

Jim Jones · Answer 2 · 2021-06-17T05:56:26.987

Welcome to SO.

Your problem might be somewhere else. ST_Distance with two geometries using the SRS 32613 returns the distance in metres:

SELECT ST_Distance('SRID=32613;POINT(508654.55672303465 4390740.143711988)',
                   'SRID=32613;POINT(508654.55672303480 4390740.143711988)');

     st_distance      
----------------------
 1.74622982740402e-10
(1 row)

It also works using ST_Transform

SELECT ST_Distance(
    ST_Transform('SRID=4326;POINT(-104.89910 39.66643)',32613),
    ST_Transform('SRID=4326;POINT(-104.89907 39.66643)',32613));
   st_distance    
------------------
 2.57321026907276
(1 row)

Demo: db<>fiddle

Are you perhaps mixing the order of the coordinate pairs? Remember, it is longitude, latitude, not the other way around. If the geometries are correct, please post a WKT literal from both geometries, so that we can reproduce your environment. Another option would be to use geography instead of geometry, which would automatically return the result in metres, but you would need to transform the geometries encoded in 32613 in a lon/lat coordinate system to make the cast work, such as 4326.

EDIT: Read carefully the answer of @JGH - he might have found the real issue. You're probably using the coordinates with a wrong SRS!

Can someone tell me why this keeps returning degrees instead of meters?

2 Answers2