Thanks, I tried your suggestion and it looks like the following works:
Max(x + y) => upper right
Min(x + y) => Lower Left
Max(abs(x - y)) => Upper Left
Min(abs(x - y)) => Lower Right
Armin
On 26/02/2009 22:11, Martin Davis wrote:
Or perhaps more simply, you can test the points using the following
criteria:
Max(x + y) => upper right
Min(x + y) => Lower Left
Max(abs(x - y)) => Lower Right
Min(abs(x - y)) => Lower Left
Sufficool, Stanley wrote:
Pull the centroid of the geometry and use generate_series() / pointn()
to "explode" the points and test each point for above & right of
centroid, above and left of centroid, etc...
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Armin Burger
Sent: Thursday, February 26, 2009 11:57 AM
To: PostGIS Users Discussion
Subject: [postgis-users] order of points in ST_ConvexHull
Hello
I need to find a possibility to identify upper-left, upper-right,
etc. corners of +/- rectangular polygons. I.e. polygons with
guranteed just 4 corners, but with a shape that is typically between
a rectangle and a rhomb. The polygons define the geometry of image
boundaries ("image footprints"). But it cannot be guaranteed which
point in the polygon corresponds to which corner since the order of
points during geometry creation is unknown.
One idea was to use ST_ConvexHull(geometry) since for this very
simple polygons the convex hull seems to be identical with the
geometry. It looked to me that the order in this convex hull was:
lower-right, lower-left, upper-left, upper-right
Does anybody know if this order is always like that or can this order
change? Would anybody know another method to identify which point of
the polygon corresponds to which corner?
Regards
Armin
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