I was thinking the same thing!
strk wrote:
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.
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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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