Hi Bill and everyone, We have an application where we need to know if a polygon intersects another polygon by a 'reasonable amount' - in this case 10%. The existing Bureau application does this by internally rendering both polygons and testing for pixels being overwritten. After some head scratching, it seems that this includes a clipping problem. All the google search results were scary, and the clipping I did at uni was the special case of clipping against a view pyramid, which is easier. We need to clip against an arbitrary polygon. Looking at DelaunyCustom, there is a clip method, but it says it clips against a half plane (is that like a flat hobbit?). Has anyone done any work in visad to clip a polygon against another polygon? Alternately, is there a good way of knowing how much two polygons intersect by? By the way, some of our polygons are representing state and council boundaries, so they have hundreds of vertices. thanks, Andrew. -- Andrew Donaldson Email: A.Donaldson@xxxxxxxxxx Bureau of Meteorology Phone: +61 3 9669 4537 P.O. Box. 1289K/150 Lonsdale St, Fax: +61 3 9669 4128 Melbourne, Australia.