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

[Paul Ramsey]

I don't the polygon you've draw means what you think it does.

POLYGON((-90 -80, 90 -80, 90 10, -90 10, -90 -80))

For example, you probably figure the first segment, -90 -80, 90 -80 runs
east-west between two points close to the south pole. In fact, it runs
directly over the south pole, so actually to the south of your point of
interest.

P


On Sun, Feb 19, 2017 at 7:36 PM, Sebastien Delaux <s.delaux at metocean.co.nz>
wrote:

> 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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