[geos-devel] Union problem

strk at refractions.net strk at refractions.net
Thu Jul 27 21:54:39 EDT 2006


On Wed, Jul 12, 2006 at 05:23:52PM -0600, Charlie Savage wrote:

> Why would the union of the same two geometries be different depending on 
>  whether you use the C API versus the C++ API?

The C-API uses a wrapper for binary operations that tries
to handle topology exceptions (usually due to robustness issues).

> >The unhappy messages you're seing are in fact very happy ones :)
> >It's the new code handling robustness problems by trying different
> >reduction or simplification. Your logs seems to reveal that a topology
> >preserving simplification with a tolerance of 0.04 did it.
> >Seems nice (you should look at results to actually tell if we like it)...
> 
> Sorry, don't understand.  Where is this tolerance set in doing a Union? 
>     How do I control it through the C API?

There's no way to control that, it's a "try all you can on topology exception"
approach. See geos/geom/BinaryOp.h for more info.

--strk;



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