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<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">Hi there,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">I am experimenting with ST_ConcaveHull, am using Postgres 9.2.2 on windows with postgis 2.1.1 r12113<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">i have a table of 218 points forming roughly an arc (something like the nike swoosh)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">when i ask for the concave hull i'm expecting a poly shrink-wrapped to them, however this is not the case, even when i set a very low percentage area parameter. for example:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">SELECT ST_ConcaveHull(ST_Collect(geom), 0.000001) as geom FROM points;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">i attach a screenshot of the points and the convext hull, as well as an sql dump of the points themselves.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">also as a side note, in researching the problem i upgraded from postgis 2.01 to 2.1.1 and noticed a change in the processing time for the above statement from 1 minute to ~ 5 minutes.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">are there any pointers for making ConcaveHull more 'aggressive' ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">thanks and regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU">-i<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU"><o:p> </o:p></span></p>
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