[postgis-users] Geography point to polygon st_distance for a polygon crossing the equator

[Sebastien Delaux]

Hi all,

I am new to postgis and I am interested in finding all the points that are
located at x metres or less of a polygon that are stored in my postgres
database.
As I am working with data located all over the world and want to work with
distances in metres I decided to use the geography type.

I am trying to understand why the following query returns 0 when the point
is clearly not included in the polygon:
SELECT ST_Distance(ST_GeographyFromText('SRID=4326;POINT(0.
-82.)'),ST_GeographyFromText('SRID=4326;POLYGON((-90 -80, 90 -80, 90 10,
-90 10, -90 -80))'));

I suspect this has something to do with the polygon crossing the equator as
SELECT ST_Distance(ST_GeographyFromText('SRID=4326;POINT(0.
-82.)'),ST_GeographyFromText('SRID=4326;POLYGON((-90 -80, 90 -80, 90 -10,
-90 -10, -90 -80))'));
returns a plausible distance.

Would anybody know whether my polygon is violating some assumption or
whether there is any other reason that I am getting those results?

Thanks

Sebastien
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