I'm not quite clear to me what you are trying to demonstrate - do you want to know the density of the points... relative to their total size (area / number?), or relative to some defined area?
cheers Ben On 28/05/2011, at 6:19 AM, Aren Cambre wrote: > Did anyone have thoughts on this? :-) > > Aren > > On Wed, May 4, 2011 at 2:12 PM, Aren Cambre <a...@arencambre.com> wrote: > The more I think about it, is this a job for R? I know I need to start using > R at some point, just haven't begun yet. > > Aren > > > On Wed, May 4, 2011 at 1:42 PM, Aren Cambre <a...@arencambre.com> wrote: > Suppose you have a geometry type with a multipoint. How would you calculate > the variance of the points in that multipoint? > > I looked through the PostGIS 1.5 function reference and am not coming up with > any easy way. > > A hard way seems to be using st_centroid(multipoint) to find the multipoint's > center. From there, I can calculate the distance of each point from its > center, and use that towards calculating the variance (each distance is > squared, all squared distances are added together, then divide by number of > points). > > I guess my ultimate need is to measure relative dispersion of multipoints. > The multipoints that have the most dispersion are suspect, but I need a way > of identifying which ones are like this. > > Aren > > > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users
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