[postgis-devel] ST_ConcaveHull in GEOS

[Paul Ramsey]

> On Jan 26, 2022, at 9:39 AM, Regina Obe <lr at pcorp.us> wrote:
> 
> Thanks all.  I’ll try to take a look at this in next couple of days and compare it to some of the tests I have done with existing ST_ConcaveHull.
>  
> And Paul to be honest with you, if you just want to put your code in PostGIS master (rip out the old for GEOS 3.11), would save me and I think  a lot of people, a lot of hassle.  Anyone who disagrees, please chime in.
> I can always test the old ST_ConcaveHull on the 3.2 branch, so having yet another branch to try out is just very time consuming.

That's great, I'm super happy to do this :) I'm going to run a few side-by-sides today/tomorrow to have some pictures to at least have an idea of the before/after, but the results of Martin's algo visually seem "right" so I don't anticipate much other than that the results at a particular "ratio" value will necessarily be a little different since mechanisms are so different.

P

>  
> It’s probably not saving too many people any trouble either because most people are not running GEOS 3.11 so wouldn’t notice the difference.
>  
> We are like at least 8 months away from a 3.3 release, so the sooner you get it in there the better.
>  
> Thanks,
> Regina
>  
> From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On Behalf Of Martin Davis
> Sent: Tuesday, January 25, 2022 7:05 PM
> To: PostGIS Development Discussion <postgis-devel at lists.osgeo.org>
> Subject: Re: [postgis-devel] ST_ConcaveHull in GEOS
>  
> For some more background on the (potential) new Concave Hull algorithm, see:  
>  
> https://github.com/locationtech/jts/pull/823
> http://lin-ear-th-inking.blogspot.com/2022/01/concave-hulls-in-jts.html
>  
>  
>  
>  
>  
> On Tue, Jan 25, 2022 at 2:38 PM Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>> Hey all,
>> The native ST_ConcaveHull in GEOS is in GEOS main now, so I have hooked it up into PostGIS in this branch
>> 
>> https://github.com/pramsey/postgis/tree/master-concavehull
>> 
>> 
>> Under this function for now.
>> 
>> CREATE OR REPLACE FUNCTION _ST_GEOSConcaveHull(
>>   geom geometry, 
>>   area_ratio float8,
>>   allow_holes boolean DEFAULT false)
>> 
>> I would like to just flip the old ST_ConcaveHull out and replace it with the new one, for folks with GEOS 3.11+, but I figured an interval to look at them side by side for a while on a test branch might be appreciated. Currently the case of point inputs is worth looking at. Polygon inputs that respect the polygon are (hull doesn't cross interior of input polygon) coming down the line.
>> 
>> P
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