[postgis-users] Re: postgis-users Digest, Vol 53, Issue 9

[Ragi Y. Burhum]

>
>
> Date: Thu, 8 Mar 2007 15:30:13 -0500
> From: "Abe Gillespie" <abe.gillespie at gmail.com>
> Subject: [postgis-users] OT: Algorithm Suggestion
> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Message-ID:
>         <a6d397e30703081230g2c048551v6d148e3546dd8241 at mail.gmail.com>
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>
> Hey all,
>
> This is definitely off topic so please ignore if you could care less.
> I'm not really sure where to go for this advice so PostGIS gets my
> abuse.  Sorry.
>
> I'm looking for a GIS algorithm (or an idea of an implementation) that
> clumps scattered, overlapping point data into simple clumps that do
> not overlap.
>
> For instance:
> Say we have a point for every building and house in a city.  Initially
> we start zoomed such that the city boundary is entirely in view.  At
> this view I'd like to have single non-overlapping points that
> represent clumps of buildings.  Now say a specific clump right
> downtown gets my attention.  I want to zoom in there and get a closer
> look.  As I zoom in the clumps break apart into new clumps.
> Eventually I'll zoom in enough to where the clump points are just each
> single building.
>
> At the most extreme zoomed-out level you'd see one single clump point
> representing every single building (imagine you're zoomed way WAY
> out).  At the most extreme zoomed-in level you'd have each individual
> building point.
>
> The biggest requirement here is having no points overlapping at any
> zoom level.  The exact placement of these clumps is not an issue
> though it should be roughly the average x,y of all the points the
> clump represents.
>
> Is there any algorithm in the GIS space that solves this problem?  It
> doesn't seem like a very unique problem, but I've never run across it.
> Perhaps even PostGIS can do this (though I'm really looking for a
> general solution)?
>
> Also, adding to the complexity is the fact that my point locations are
> dynamic.  So I couldn't just set up a set of layers for set zoom
> levels.  I.e. the algorithm would have to run every time the map is
> rendered.
>
> Thanks for your help / ideas!
> -Abe
>
>

Gotta love Google Scholar; Search for Cartographic Generalization
Algorithms.
http://scholar.google.com/scholar?hl=en&lr=&safe=off&q=Cartographic+generalization+algorithms&btnG=Search

Hope this helps,

- Ragi Y. Burhum
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