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From: Allen <ajhalldeleteme@gmail.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Area of specific pixel color?
Date: Mon, 24 Mar 2008 20:48:05 -0500
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Hi Walter,

You're very right to be concerned about the foreshortening.  Basically, 
due to the projection of the surface onto the view-plane (since I'm 
looking down the z-axis), the areas will be altered into their 
projection.  If the selection algorithm is exactly perfect, then I'll 
get exactly the area of desire, and the foreshortening will not affect 
the results.  However, if there is some error in the selection process, 
you're absolutely correct.

I determine bounds for the selection angles (surface normals), and this 
highlights the regions of interest for me.  These bounds are the perfect 
way to express your error as you suggested.  I'll definitely implement 
that in my work!

Thanks for your thoughts, Walter!  I appreciate them!  :)
-Allen

Walter Roberson wrote:
> I am concerned about the foreshortened areas. I see that there
> are corrections for it posted ("divide by the cosine of the angle")
> but there will be angles for which there would be considerable
> error inherent in that process. In your particular application,
> would it make sense to produce an error estimate as part of
> the output? For example "The boundary that would have produced
> one less pixel coloured would have been Xn and the boundary
> that would have produced one more pixel coloured would have been Xf
> so the true area is between Xn/cos(angle) and Xf/cos(angle)" ??