Silhouette of a facetted polyhedra

[Dickinson, John]

I want to get the shadow or projection of a 3D facetted polyhedra on a
plane.  In other words I want to project all the triangles that describe the
surface of the polyhedra onto a plane and union them so that I have a
polygon possibly with inclusions or holes (e.g. project a donut onto a plane
perpendicular to the axis of its hole).

Can anyone point me to some code or papers that would give decent algorithms
for doing this (specifically the union of all the facets into a polygon)?

The goal of this is to determine the centroid and area of the resultant
projection.  Is there a way to do this without building the projected
polygon first?

John

--
-((Insert standard disclaimer here))-|--- Washington Irving (1783-1859) ----
John Kenneth Dickinson               |   "A sharp tongue is the only
Research Council Officer  IMTI-NRC   |    edge tool that grows keener
email: john.dickinson at nrc.ca         |    with constant use."
http://publish.uwo.ca/~jkdickin/     |



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