Silhouette of a facetted polyhedra

[Dickinson, John]

Thanks for the pointer.  I checked out your online abstracts an they look
impressive but not really along the line or simplicity of what I am looking
for.  I can reduce my task to the more simple problem of unioning many
triangulare planar facets together and then working with the resulting
polygon.

Of course, calculating the union of an unordered list of triangle facets on
a plane can be very expensive if not done correctly.

John

-----Original Message-----
From: Steven Spitz [mailto:StevenS at proficiency.com]
Sent: Wednesday, April 11, 2001 4:07 AM
To: 'Dickinson, John'
Subject: RE: Silhouette of a facetted polyhedra



John,

It sounds like you are interested in related problems from computer
graphics: shading, visibility, and accessibility.  I personally did some
work in accessibility, but used discrete techniques.  You can find papers
at: http://www-pal.usc.edu/html/publications.html or
http://www-pal.usc.edu/~spitz

Steven

> -----Original Message-----
> From: Dickinson, John [mailto:John.Dickinson at nrc.ca]
> Sent: Monday, April 09, 2001 3:27 PM
> To: 'compgeom-discuss at research.bell-labs.com'
> Subject: Silhouette of a facetted polyhedra
> 
> 
> 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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