[geos-devel] Bug in buffer function?

[Silke Reimer]

Hallo again,

I know that usually it is not really helpful to submit a request twice but in 
this case I give it a try by formulating the request slightly different: Can 
anybody please try just to through the below mentioned polygons into the 
corresponding geos function and confirm the behavior? All I want to know is, 
whether this is really a bug or whether I just oversee something. 

(If I get no answer to this email I will just add this example to the bug 
tracker.)

Thanks,

	Silke

See here again the original post:

On Friday 25 January 2008, Silke Reimer wrote:
> Hallo!
>
> I observed a really strange behavior of the buffer function when using an
> inner buffer. The error occurs with the following geometry:
> POLYGON ((
> 513.4 343.1,
> 707.3 344.2,
> 707.0 394.9,
> 797.9 395.4,
> 799.2 341.8,
> 516.9 340.9,
> 516.7 262.3,
> 513.2 262.3,
> 513.4 343.1
> ))
> Its WKB representation is
> 0103000000010000000900000033333333330B80409A9999999971754066666666661A86403
>33333333383754000000000001886406666666666AE78403333333333EF88406666666666B67
>8409A99999999F98840CDCCCCCCCC5C7540333333333327804066666666664E75409A9999999
>9258040CDCCCCCCCC6470409A99999999098040CDCCCCCCCC64704033333333330B80409A999
>99999717540
>
> Using a buffer of -2 should lead to an inner buffer but leads
> to "GEOMETRYCOLLECTION EMPTY" resp. "POLYGON( EMPTY)" depending on the geos
> version.
>
> Using the same buffer of -2 on a polygon with the same shape but shifted to
> the left by 100 and shifted down by 100, i.e.
>
> POLYGON ((
> 413.4 243.1,
> 607.3 244.2,
> 607.0 294.9,
> 697.9 295.4,
> 699.2 241.8,
> 416.9 240.9,
> 416.7 162.3,
> 413.2 162.3,
> 413.4 243.1
> ))
>
> resp.
> 010300000001000000090000006666666666D679403333333333636E406666666666FA82406
>666666666866E400000000000F8824066666666666E72403333333333CF85406666666666767
>2409A99999999D985409A99999999396E4066666666660E7A40CDCCCCCCCC1C6E40333333333
>30B7A409A999999994964403333333333D379409A999999994964406666666666D6794033333
>33333636E40
>
> leads to the expected buffer:
> POLYGON((609.172261037685 243.512992930268,609.26383338939
> 243.821372982058,609.29996498814 244.211834112356,609.011804031568
> 292.911035772954,695.948180429531 293.389233662932,697.151062564334
> 243.793477951075,609.172261037685 243.512992930268))
> resp.
> 01030000000100000007000000DD1965CA600983408D5226706A706E403118AE541C0A83402
>AF8FDAF487A6E400A300B54660A8340DB175558C7866E405E4CB62C1808834035253F9A934E7
>2405BFC9EDF95BF8540BECC134D3A567240B72B4A6035C98540EB3EDF2B64796E40DD1965CA6
>00983408D5226706A706E40
>
> I tested this on different geos versions among them
> 3.0.0rc4 and 3.0.0
>
> I would say that this is a bug but it would be nice if somebody could
> confirm this - and perhaps you even have an idea how to solve this? I did
> not find any entry in the bug tracker but maybe I just missed it. In this
> case I would be glad for a hint.
>
> Many greetings,
>
> 	Silke



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