[R-sig-Geo] 3D grids of discrete values and corresponding polygons

[Waichler, Scott R]

Hello,

I am working with a 3D grid of a small number of discrete values, where
the grid is Cartesian (cell borders are orthogonal) but has irregular
cell width/length/height.  I would like to make plots of 2D cross
sections through the grid.  I want to show the exact outlines of
contiguous groups of like-valued cells.  A couple of years ago Roger
Bivand pointed out how to do this in 2D, using Polygon(),
unionSpatialPolygons(), and other functions.  Is there a way to do this
with a cross section taken through the 3D grid in one of the principal
directions?  I don't see mention or examples of 3D polygons.  Or do I
need to derive the polygons and union them separately for each cross
section?

Also, is there an easy way to search the R-sig-geo archives?

Thanks,
Scott Waichler
Pacific Northwest National Laboratory
scott.waichler at pnl.gov