[R] GIS re-mapping / polygon overlap

[Hisaji Ono]

Hi.

 How about GEOS available at.

 http://geos.refractions.net/

GEOS supports hole for clipping.

 I could build it in MiGW.

 However I've only executed demo codes.


----- Original Message ----- 
From: "Ross Ihaka" <ihaka at stat.auckland.ac.nz>
To: "Jens Oehlschlägel" <oehl_list at gmx.de>
Cc: <r-help at stat.math.ethz.ch>
Sent: Friday, October 24, 2003 6:13 AM
Subject: Re: [R] GIS re-mapping / polygon overlap


> Jens Oehlschlägel wrote:

> >     - is there an efficient R function that can determine the amount of
area
> > overlap between two general polygons (beyond gpclib)
> >
> > I am willing to share developed code for this problem (that's why I
would
> > prefer gpl code over gpclib, which is not really free)

>
> There is pretty cool polygon intersection algorithm available at:
>
> http://davis.wpi.edu/~matt/courses/clipping/4th.html
>
> with the code at:
>
> http://davis.wpi.edu/~matt/courses/clipping/code.html
>
> You can pick up the paper the code is based on from kai hormann's home
> page (currently):
>
> http://vcg.isti.cnr.it/~hormann/
>
> The only problem with the algorithm is that it doesn't handle holes, but
> for area computations you could just join the holes to the boundary.
>