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

[Sebastien Delaux]

Thanks for your reply Paul.
Yes, that's what I thought. That would explain why (0,-82) is inside the
polygon.
Nevertheless, if my first segment runs through the south pole, then I would
expect both of the queries mentioned in my initial post to return 0 which
is not the case.

Sebastien

On Mon, Feb 20, 2017 at 4:56 PM, Paul Ramsey <pramsey at cleverelephant.ca>
wrote:

> 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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>
>
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