[postgis-tickets] [PostGIS] #5235: A problem in unit handling in Geography type

[PostGIS]

#5235: A problem in unit handling in Geography type
-----------------------+--------------------------------
 Reporter:  sergeyt    |      Owner:  pramsey
     Type:  defect     |     Status:  new
 Priority:  medium     |  Milestone:  PostGIS PostgreSQL
Component:  postgis    |    Version:  3.2.x
 Keywords:  geography  |
-----------------------+--------------------------------
 Geography type does not take into account units of the GCS. It assumes the
 units to be the degrees. There are some GCS that use other units. For
 example, 4807 (https://spatialreference.org/ref/?search=epsg:4807) uses
 grads instead of degrees. Here is a bug:
 Perform distance on two points defined in 4326
 SELECT ST_Distance(
   'SRID=4326;POINT(0 0)'::geography,
   'SRID=4326;POINT(1 0)'::geography
   );
 Result is 111319.49079327, which is expected on degree at equator.

 Transform the points to 4807 and calculate the distance:
 SELECT ST_Distance(
   ST_Transform('SRID=4326;POINT(0 0)', 4807)::geography,
   ST_Transform('SRID=4326;POINT(1 0)', 4807)::geography
   );
 Result is 123687.23083618. This is 10% larger than expected.

 Transformation from 4326 SELECT ST_AsText(ST_Transform('SRID=4326;POINT(0
 0)', 4807)); produces a point in GRADS: "POINT(-2.596322435214223
 -0.003215804261427)". Cast to geography apparently does not convert it to
 degrees.

 So either the geography operator should do conversion of grads to degrees
 or the Geography type itself should be taking into account the units of
 the GCS.
-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/5235>
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