I have used an R function before (using maptools package) to do something similar, but I can't remember the details, so I would be considering looking at PL/R.
cheers Ben On 06/05/2010, at 15:40 , strk wrote: > On Mon, May 03, 2010 at 10:49:32PM -0600, John Abraham wrote: >> One of the things I miss about using ESRI's GIS is the ability to do >> dot-density maps. Within a polygon, the number of dots is proportional to a >> value, and the dots are randomly placed. I find it useful to be able to >> present several data values at once (e.g. blue dots for population, red dots >> for employment). >> >> I also find that it is a more intuitive way of scaling for zone size than >> dividing the value by the area of the zone. That is, the count of the dots >> represents the actual number, but the density of the dots represents the >> density of the number. So I don't have to decide whether to divide the >> value by the area of the polygon to plot density: both the absolute number >> and the density are easily visible. >> >> Since my open-source GIS viewing systems (mostly QGIS and Mapserver) won't >> plot dot-density, I've done without. >> >> But today I realized that I can build these on the server instead. I can >> generate random points within the bounding-box of the polygon, throwing out >> those that aren't contained within the polygon, repeating until I have >> enough. Then I can save these points as a separate layer, and display this >> layer using almost any desktop or web based viewer! >> >> Has anyone done this? Can I do it in SQL or do I need to write something in >> PL/pgsql? > > PL/pgsql would be easier than SQL at the minimum. > Still, a C implementation would likely be better, for speed reasons. > > --strk; > > () Free GIS & Flash consultant/developer > /\ http://strk.keybit.net/services.html > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
