Geometry Boost List: [ggl] Quick question about bg::difference

Subject: [ggl] Quick question about bg::difference
From: V D (zedxz2)
Date: 2011-10-24 20:21:25

Hum, after running more test cases here is what seems to happen:

bg::difference(MultiPolygon, Polygon) and bg::difference(Polygon, MultiPolygon) will return always return the polygon if they are disjoint.
bg::difference(Polygon, Polygon) will always return the 1st polygon if they are disjoint.

-v

On Oct 24, 2011, at 2:06 PM, Barend Gehrels wrote:

> Hi,
> 
> On 24-10-2011 22:47, V D wrote:
>> Hi,
>> 
>> 
>> I have a question about the difference algorithm.
>> 
>> template<typename Geometry1, typename Geometry2, typename Collection>
>> void difference(Geometry1 const & geometry1, Geometry2 const & geometry2, Collection & output_collection)
>> 
>> 
>> What happens in the case that the 2 geometries are disjoint? So far in my test cases it seems that in disjoint cases it will always return the second geometry, is this guaranteed ?
>> 
> 
> Hmm, I would expect they would always return the first. That is what OGC specifies. Are you sure? I will look tomorrownight, and repair if necessary.
> 
> Regards, Barend
> 
> 
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