[geos-devel] Buffering Multipolygons

Chris Hodgson chodgson at refractions.net
Tue May 17 12:36:06 EDT 2005

I think Martin Davis is off on holidays, so I will offer this tidbit - I 
do recall that some JTS operations (union/intersection come to mind) do 
NOT work on multi-polygons. I wouldn't be surprised if buffer was also 
one of these operations.

The only convex hull algorithm I know works on a set of points, if a 
similar one is used in JTS then it probably would work on any type of 
shape, (even multi-*) because you would just break it down into the 
constituent points.

My best bet is that you're code is right Steve - if you can buffer 
regular polygons, and you can convex hull multi-polygons, then it seems 
more likely to me that buffering multi's just doesn't work than it is 
that there is some special case not being handled in your code :)


Steve Lime wrote:
> Hi All: I'm wondering if someone can confirm that buffering a
> multipolygon works with GEOS 2.1.1. I'm testing my conversion code and
> am having problems with just this case: simple polgons with/without
> holes work fine, anything with multiple outer rings does not (bus error
> on Mac OS). The conversion code must be close because computing a convex
> hull on the same test shape works fine.
> I've attached a small graphic that shows the multipolygon (with GEOS
> computed convext hull)...
> Steve
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