[postgis-users] Roeck test

[Pedro Doria Meunier]

Bruce,

You're absolutely right ;-)

Regards

-- 
Pedro Doria Meunier <pdoria at netmadeira.com>





On Fri, 2008-10-24 at 12:25 -0600, Bruce Rindahl wrote:
> After a quick look at the links, couldn't a stored procedure
> (function) be used here?  I envision the input is a polygon, grab the
> outside ring, explode the vertices's to get a set of points(all
> existing functions).  Then the collection of points could be looped
> through with the algorithm described to return a center and radius
> which could then give a circle (buffer).
> Or am I on drugs here..
> Bruce
> 
> 
> Lee Meilleur wrote: 
> > Yes and yes to both questions, but the Roeck test is required by some states.  And some states don't allow their politicians to draw their political boundaries.
> > 
> > Thanks Martin, I'll test the convex hull and compare with the Roeck from our commercial software.
> > 
> > Brent, thanks for the link, not sure if Paul will get the algorithm into the final release of PostGIS 1.3.4.  I have two years to figure this out.
> > 
> > 
> > -----Original Message-----
> > From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Martin Davis
> > Sent: Friday, October 24, 2008 11:40 AM
> > To: PostGIS Users Discussion
> > Subject: Re: [postgis-users] Roeck test
> > 
> > 
> > Wouldn't it be easier and more accurate to use the convex hull of the polygon instead of the minimum enclosing ball? The CH will have smaller area (i.e. be a tighter bound on the area covered by the polygon), so it seems like it would give a more accurate basis for comparison.
> > 
> > Lee Meilleur wrote:
> >   
> > > Has anyone calculated the Roeck test using PostGIS?  This is an area
> > > based measure that computes the ratio of the area of a polygon to the
> > > area of the minimum enclosing circle for the polygon.  It's used to
> > > measure compactness of districts for redistricting applications,
> > > basically a way to test for gerrymandering.  Thanks.
> > > 
> > > Lee Meilleur
> > > LCC-GIS Office
> > > Minnesota Legislature
> > > 100 Rev. Dr. MLK Jr Blvd.
> > > 55 State Office Building
> > > St. Paul, MN 55155
> > > 651.296.0098  Fax: 651.297.3697
> > > lee.meilleur at gis.leg.mn
> > > http://www.gis.leg.mn
> > > 
> > > 
> > > _______________________________________________
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> > > http://postgis.refractions.net/mailman/listinfo/postgis-users
> > > 
> > > 
> > >     
> > 
> > --
> > Martin Davis
> > Senior Technical Architect
> > Refractions Research, Inc.
> > (250) 383-3022
> > 
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> > 
> >   
> 
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