[postgis-users] Spatial operators

[Luis Mota]

Thanks.

What I am trying to do is to find i if a point is to the left or right 
of a linestring... Which is a tricky question... The problem is that I 
have some zip-code data (from a third party) which is coded as sth like 
left_zip and right_zip. As I am trying to get the address of a point, I 
need to find if this point lies on the left or right... I am assuming 
that these left/right concepts are valid when you look 'from' the 
startpoint 'to' the endpoint of the linestring...

For now, I suspect that these spatial operators are of no use in this 
case... I will have to deal with this in a different way... Any suggestions?

Bye, Luís

David Blasby wrote:

>Luis,
>
>The operators are very simple and work on the bounding box of the
>geometry.
>
> A&<B  - true if xmax(A) < xmax(B)
>
>A<< B  - true if xmax(A) < xmin(B)
>
>And the same for A&<B and A>>B.  There are no operators that work in the
>Y direction.
>
>The reason these operators exists is to mimic the normal database
>operators "<" and "<=".  They dont really have any practical use.
>
>If you want to sort things by Y, I would do something like:
>
>SELECT the_geom FROM mygeom ORDER by ymax(the_geom)
>
>The xmax(geom), ymax(geom), xmin(geom), ymin(geom) returns information
>about the bounding box of a geometry.
>
>dave
>
>
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