[geos-devel] Unary Union (was: rgeos interface to R classes)

[Sandro Santilli]

On Fri, Feb 5, 2010 at 12:29 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
> On Fri, 5 Feb 2010, strk wrote:
>
>> On Mon, Feb 01, 2010 at 09:48:57AM -0800, Martin Davis wrote:
>>
>>> The technique of using buffer(0) to union polygons is now deprecated in
>>> favour of using Unary Union (Geometry.union() - not sure what the exact
>>> GEOS signature is).  Unary Union is usually faster and more robust than
>>> the previous technique.  You might want to check this out.
>>
>> Uhm, I might have missed this in my last port (either completely
>> or just the outer interface). Is the JTS repository finally landed
>> so to take a look ? I'm interested in evaluating its use for "geometry
>> cleanup" purposes (http://trac.osgeo.org/postgis/ticket/399)
>
> Seems to be in the 3.2.0/1.6.0 C API as GEOSUnionCascaded(), and works like
> the buffer trick for me (except for my unsolved scale problem).

I've checked the GEOS code. It's actually NOT the same classes being
used for CascadedUnion and UnaryUnion. Dunno about the actual
output characteristic, but it's surely documented (in JTS) to be different
from the buffer trick.


--strk;

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