ST_RandomPoinsOnSurface(geometry, numpoints) would be an interesting function indeed. Sounds like a good job for GEOS/JTS.
--strk; 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? > > -- > John Abraham > > PS I just bought the Postgis In Action book; enjoying it so far. > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users -- () Free GIS & Flash consultant/developer /\ http://strk.keybit.net/services.html _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
