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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).<br>
Or am I on drugs here..<br>
Bruce<br>
<br>
<br>
Lee Meilleur wrote:
<blockquote
cite="mid:EE2E75216F55D2458F566BD899F5DECAB6E1EC1B65@mail.lcc.local"
type="cite">
<pre wrap="">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: <a class="moz-txt-link-abbreviated" href="mailto:postgis-users-bounces@postgis.refractions.net">postgis-users-bounces@postgis.refractions.net</a> [<a class="moz-txt-link-freetext" href="mailto:postgis-users-bounces@postgis.refractions.net">mailto:postgis-users-bounces@postgis.refractions.net</a>] 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:
</pre>
<blockquote type="cite">
<pre wrap="">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
<a class="moz-txt-link-abbreviated" href="mailto:lee.meilleur@gis.leg.mn">lee.meilleur@gis.leg.mn</a>
<a class="moz-txt-link-freetext" href="http://www.gis.leg.mn">http://www.gis.leg.mn</a>
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<pre wrap=""><!---->
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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