[Fwd: [postgis-users] Density calculation]

[Adrian Custer <acuster nature berkeley edu>]

Hey Everyone,

The mention of pivot tables and statistical calculation made me think of
gnumeric. This sounds like a pretty basic spatial statistical analysis
that gnumeric would benefit from having. I imagined one of the
math/stat/code brainiacs on the list might enjoy playing with the idea.

cheers,
adrian


-----Forwarded Message-----

From: Uli Mueller <uli mueller gmx ch>
To: postgis-users postgis refractions net
Subject: [postgis-users] Density calculation
Date: 10 May 2003 09:59:31 +0200

Hi

I am trying to calculate a density surface from points in a postgis
database. The result should be stored in a new table in PostGIS and should
display in MapServer. Any ideas about a fast way to do this in a
PostGIS/PHP/MapScript-environment?

I would prefer to do the whole calculation directly within SQL (for matters
of speed and reusability in different projects). I have been experimenting
with creating a temporary pivot table representing a matrix of all x- and
y-coordinates of my study area. Then I calculate the number of points within
a given radius from each matrix cell. Principally, this approach works, but
of course it tends to be very slow. I would appreciate to know about a
better solution.

Uli
----


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