Polygon difference

[johnny xia]

Hi,

I am using shapely.geometry for Pytong to do some polygon operation. Here is a short description of my problem is:

I have a Polygon A, B, C. B and C is contained in A. Now I want to calculate the polygon of (A - (B + C) ). If result Polygon has holes, I want to convert it to a MultiPolygons.

Any idea about how to use shapely.geometry to resolve the above problem.

--
Thanks,
Johnny Xia.

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[Sean Gillies-2]

On Sep 11, 2009, at 8:00 AM, johnny xia wrote:

> Hi,
>
> I am using shapely.geometry for Pytong to do some polygon operation.  
> Here is a short description of my problem is:
>
> I have a Polygon A, B, C. B and C is contained in A. Now I want to  
> calculate the polygon of (A - (B + C) ). If result Polygon has  
> holes, I want to convert it to a MultiPolygons.
>
> Any idea about how to use shapely.geometry to resolve the above  
> problem.
>
> --
> Thanks,
> Johnny Xia.

Hi Johnny,

More or less like this:

   x = A.difference(B.union(C))

Holes of the resulting polygon (x) can be accessed via the `interiors`  
attribute:

   http://gispython.org/shapely/manual.html#id52

Cheers,
Sean

--
Sean Gillies
Programmer
Institute for the Study of the Ancient World
New York University

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