That makes sense, thanks for the explaination. And yep, I'm using NTS.
On Wed, Mar 4, 2009 at 11:41 AM, Martin Davis <[email protected]>wrote:
> I notice you're using NTS (right?)... The behaviour in JTS is slightly
> different - it returns a POLYGON EMPTY.
>
> Simplification always returns a geometry of the same type as the input
> geometry, and by default it attempts to ensure valid topology (by applying
> a buffer(0) - which is a bit of a hack, I admit). This is why it returns an
> empty polygon.
>
> You can prevent the validity enforcement by using
> DouglasPeuckerSimplifier.setEnsureValid(false)
>
> AFAIK there's no clear standard on how to handle degenerate cases like this
> - different use cases might require different kinds of output. You should
> check for degenerate input first and convert it according to your precise
> need.
>
> Jeff Adams wrote:
>
>> It shouldn't have been zero, although I don't actually know what it was
>> (It was due to a bug in my code, that has since been fixed).
>> However I just tried to reproduce it with a test case and simplify seems
>> to return an empty geometrycollection (which seems like resonable behavior,
>> although better behavior might be to produce a single point at the center).
>> So perhaps I was mistaken about exactly what was going on... It makes me
>> wonder if my code that calls simplify is not correct ;-). I'll let you know
>> if I am able to reproduce this again.
>>
>> Here is my simple test case if you want to mess around with it:
>>
>> [Test]
>> public void TestSimplifyBadPoly()
>> {
>> Polygon p = new Polygon(new LinearRing(new ICoordinate[] {
>> new Coordinate(1, 1), new Coordinate(1, 1),
>> new Coordinate(1, 1), new Coordinate(1, 1),
>> new Coordinate(1, 1)}));
>> Console.Out.WriteLine("Bad polygon: " + p);
>> IGeometry simpleP = DouglasPeuckerSimplifier.Simplify(p, 0.1);
>> Console.Out.WriteLine("Simple bad polygon: " + simpleP);
>> Assert.AreNotEqual(p, simpleP, "Simplify didn't do anything to
>> this invalid polygon.");
>> }
>>
>>
>> On Tue, Mar 3, 2009 at 11:39 AM, Martin Davis
>> <[email protected]<mailto:
>> [email protected]>> wrote:
>>
>> What was your simplification tolerance? If it was 0 as well, then
>> nothing would be changed.
>>
>> If not, this might be a bug - although this is a bit outside what
>> would be considered as reasonable input to a simplification routine.
>>
>> Jeff Adams wrote:
>>
>> - Show quoted text -
>> I have some code that creates "circle" polygons given a
>> center, radius, and number of points. The circle gets passed
>> to some other code that happens to simplify the polygon (using
>> DouglasPeucker).
>>
>> I accidentally wound up calling this code with a radius of
>> zero. This produced a 46-point polygon where all the points
>> were identical. What was surprising to me is that the
>> simplifier didn't seem to change it at all. I would have
>> expected it to return a single point, or throw an exception,
>> or something. Is this (doing nothing) the expected behavior?
>>
>> Thanks,
>> Jeff
>>
>> ------------------------------------------------------------------------
>>
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>>
>> -- Martin Davis
>> Senior Technical Architect
>> Refractions Research, Inc.
>> (250) 383-3022
>>
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>>
>>
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>>
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>>
> - Show quoted text -
>
> --
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022
>
> _______________________________________________
> jts-devel mailing list
> [email protected]
> http://lists.refractions.net/mailman/listinfo/jts-devel
>
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