[postgis-users] [postgis-devel] Problem in st_StriaghtSkeleton - Hangs!

[Regina Obe]

Steve,

One more thought.  Can you try this and see if it works.  I think ST_StraightSkeleton and ST_ApproximateMedialAxis are having issues, because in this case your holes are so big that it almost cuts into another.

So to work around the issue, you can subdivide the polygon and then do the analyze like this:

SELECT  ST_ApproximateMedialAxis(ST_SubDivide('POLYGON((256 760,518 760,518 630,674 630,674 
239,673 239,127 239,127 240,126 240,126 513,127 513,127 514,126 514,126 
630,255 630,256 630,256 760),(128 629,128 423,270 423,270 422,271 
422,271 240,672 240,672 629,128 629),(258 759,258 631,516 631,516 
759,258 759),(128 421,128 240,269 240,269 421,128 421))'::geometry, 12));

You might need to tweak with the subdivide param.

http://postgis.net/docs/manual-dev/ST_Subdivide.html

The subdivide cuts right into the holes turning them not into holes so you end up with simple polygons that approximate medial axis can handle.

Once you are done you can run ST_Union on your set of Linestrings.





-----Original Message-----
From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On Behalf Of Stephen Woodbridge
Sent: Wednesday, January 17, 2018 2:47 PM
To: PostGIS Development Discussion <postgis-devel at lists.osgeo.org>
Subject: [postgis-devel] Problem in st_StriaghtSkeleton - Hangs!

Hi all,

I have run into a problem using st_StraightSkelton() where it appears to hang at 100 cpu. Maybe an endless loop?

select st_straightskeleton('POLYGON((256 760,518 760,518 630,674 630,674
239,673 239,127 239,127 240,126 240,126 513,127 513,127 514,126 514,126
630,255 630,256 630,256 760),(128 629,128 423,270 423,270 422,271
422,271 240,672 240,672 629,128 629),(258 759,258 631,516 631,516
759,258 759),(128 421,128 240,269 240,269 421,128 421))'::geometry);

POSTGIS="2.3.3 r15473" GEOS="3.5.1-CAPI-1.9.1 r4246" SFCGAL="1.2.2" 
PROJ="Rel. 4.9.2, 08 September 2015" GDAL="GDAL 1.11.3, released 2015/09/16" LIBXML="2.9.3" LIBJSON="0.11.99" RASTER

Can anyone reproduce this?
Any idea how to work around it?

Is there a non-CGAL version of skeleton?

Thanks,
   -Steve

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