intersection of objects SpatialPolygonsDataFrame

Try 

?PolySet2SpatialPolygons

This function will bring the newly intersected polygon back to class SPDF
and then you should be able to attach the corresponding data.frame to the
new polygon object.

Andrew Niccolai
Doctoral Candidate
Yale School of Forestry


 
-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch
[mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of Agustin Lobo
Sent: Wednesday, April 09, 2008 9:48 AM
To: r-sig-geo at stat.math.ethz.ch
Subject: [R-sig-Geo] intersection of objects SpatialPolygonsDataFrame

Dear list,

I have two objects of class "SpatialPolygonsDataFrame"
and I want to get the intersection. The first object (x)
are circles (approached as polygons) with a fake data
frame. The circles could be just in a SpatialPolygons
object, I just put the fake data frame to get the same
class as I would have got from importing a shp file via readOGR.
The second object (absUTMpolysHABS2) is a map of habitats
(imported from a shp file
via readOGR). I want the circles to intersect the map
so that I can calculate the area of each habitat in
each circle. I'm not sure if I'm on the right path:

It seemed to me that I had to use function joinPolys()
with operation="INT" from package PBSmapping,

a <- (joinPolys(SpatialPolygons2PolySet(x), 
SpatialPolygons2PolySet(absUTMpolysHABS2)))

a looks good (circles subdivided into polygons)
but SpatialPolygons2PolySet() makes me loss the information
in the data frame of the map, so I do not know the habitat
for each polygon within each circle.

Any way to relate the new polygons to the data frame of the map?
Or should I use an entirely different apporach in R?
Or should I export x to a GIS and do this operation there?

Thanks!

Agus