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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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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