[postgis-users] Roeck test

[Bruce Rindahl]

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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>>
>>
>>     
>
> --
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022
>
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