Polygon intersection

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.



 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.

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