[R-sig-Geo] convert Map shapes to logical matrices - for set operations

[James Muller]

Hi, I have a little problem.  (and sorry for the cross-post of this)

I'm trying to do the following:
 Convert  _projected_ shapes from a Map object into logical matrices. 
That is, rasterize a shape into a logical "in-the-shape" and 
"out-of-the-shape" matrix.

What I'm trying to do is get an 'equal-area' estimate of the area of 
intersection between two overlapping shapes, without any concern about 
there being holes in the shapes. I know owin can deal with most of this, 
but for sure it doesn't support geographic projections, which will allow 
the 'equal-area' estimate to be equal.

An idea I had was to pipe the output of the maptools Map plotting 
function map into the matrix. But I really have no idea how to do that 
at this point in my R education.

Any suggestions are extremely welcome.

Cheers,

James