Geometry Boost List: Re: [geometry] difference algorithm produces invalid polygon?

Subject: Re: [geometry] difference algorithm produces invalid polygon?
From: Volker Schöch (vschoech_at_[hidden])
Date: 2012-07-17 04:20:00

Hi again,
Are there any news in this issue?
Thank you!
   Volker

--
Volker Schöch | vschoech_at_[hidden]
Senior Software Engineer
think-cell Software GmbH | Chausseestr. 8/E | 10115 Berlin | Germany
http://www.think-cell.com | phone [phone] | US phone [phone]
Amtsgericht Berlin-Charlottenburg, HRB 85229 | European Union VAT Id DE813474306
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-----Original Message-----
From: geometry-bounces_at_[hidden] [mailto:geometry-bounces_at_[hidden]] On Behalf Of Barend Gehrels
Sent: Dienstag, 6. März 2012 00:26
To: Boost.Geometry library mailing list
Subject: Re: [geometry] difference algorithm produces invalid polygon?
Hi Volker,
On 29-2-2012 15:04, Volker Schöch wrote:
>> Can you send a (WKT) sample of such a polygon? I think I understand but don't see how the x-constraint fit into this.
> MULTIPOLYGON(((1716 1554,2076 2250,2436 2352,2796 1248,3156 2484,3516 
> 2688,3516 2688,3156 2484,2796 1248,2436 2352,2076 2250, 1716 1554)))
>
> This seems to me like a more general form of the "spike only"-type polygon that I originally submitted. I merely mentioned the x-constraint to rule out any real self-intersections (and this constraint incidentially holds in my application, allowing to ensure correct order of points).
>
In the meantime I tried your polygon. The problem our library currently has with this polygon, actually with every spike (spike-only or a spikey
feature) is that it does not know which way to go. As soon as the intersection point (two at a spot) is encountered, it decides going left or write, but because of the two it can make a wrong decision.
The good news is I think this can be helped. Will study this later in more detail.
Regards, Barend