Re: how to check if a point is contained in a polygon ?

Julien Cigar wrote:
> Hello,
>
> I'm busy to work on an application where the user can select (with
> precision) an area on a map (for example the contours of a lake) and I
> have to retrieve all the data (specimen observations) within this area.
>
> I have a list of coordinates pair [(lat1, long1), (lat2, long2), (lat3,
> long3), (..., ...)] which form a polygon. In my database every specimen
> has a pair of coordinates where it has been collected.

Are you familiar with the PostGIS project - if you're doing a lot of
this, it might be worthwhile looking into.

http://www.postgis.org/

> Is there an SQL function to check if a point is contained in a polygon
> shape (before I start to write my own) ?
>
> I tried something like :
>
> rodentia=> select point '(-8,25)' <@ polygon
> '((-3,10),(8,18),(-3,30),(-10,20))';

Works both ways around here:

SELECT point '(-8,25)' <@ polygon '((-3,10),(8,18),(-3,30),(-10,20))';

SELECT polygon '((-3,10),(8,18),(-3,30),(-10,20))' @> point '(-8,25)';

I'm running 8.3, but it seems to be in 8.2 too.

Try \do '<@' from psql to see what operators are available.

--
Richard Huxton
Archonet Ltd