[R-sig-Geo] shared boundary lengths ?

[Roger Bivand]

On Mon, 26 Jul 2010, Toby.Patterson at csiro.au wrote:

> Hi, Apologies up front if this has been covered somewhere already -- I 
> have seen some discussion of a similar problem on the list, but it 
> doesn't quite seem to cover what I'm after.
>
> Also I'm new to the spatial side of R, so I might not quite use the 
> correct lingo!
>
> My problem is this:
>
> For a set of polygons (a SpatialPolygonsDataFrame) with shared 
> boundaries (i.e. with no overlapping regions or gaps between them), I 
> need to know the length of shared adjacent boundaries. Note, in this 
> case all polygons will have a boundary shared with at least one other 
> polygon.
>
> So I'm after a square symmetric matrix with diagonals zero. The i,j th 
> entry would then be the length (in some appropriate coordinate system) 
> of the boundary between polygon i and j.
>
> Also - I'm not sure if sufficient information is stored in the 
> SpatialPolygonsDataFrame class actually allow these shared lengths to be 
> calculated. I'm sure someone can quickly clear that up for me. Possibly 
> this can only be done in GIS systems?

Indeed, only in topological GIS, because the nodes and arcs must be 
identified and the topology built. The only provision in R-spatial is 
using vect2neigh() in the spgrass6 interface to GRASS6. You would need to 
install GRASS first, export the polygons to GRASS, then read off the 
neighbours and the boundary lengths with the function. As far as I'm 
aware, it doesn't work on Windows because of the inadequacy of cmd.exe 
(script variable quoting) for running v.db.addtable, but on other 
platforms works fine. The function is described in:

https://stat.ethz.ch/pipermail/r-sig-geo/2005-October/000616.html

and on its help page.

Hope this helps,

Roger

>
> Any help would be much appreciated as this it seems quite a fiddly one 
> to write myself.
>
> Thanks,
> Toby
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no