Re: [ATM] Dumb Question: how to measure a...

[George Anderson <tillerman1@videotron.ca>]

I think that Richard Schwatz would be the perfect person to provide the
ideal solution to this question. It is the type of geometric puzzle that
I think he would enjoy.

George Anderson
Montreal Canada

Clear skies and good health

Mutalib Abdallah wrote:
> 
> Circle.
> 
> Given a circle of glass, how can I measure it to characterize its
> circularity?   Assume I do not know where on the glass is the "center", if,
> in fact a center exists.
> 
> The only way I can thing of is to measure the coordinates of a large number
> of edge points, copy the data into a computer file, and then do a curve fit
> to find the circle of best fit (either rectangular or polar coordinates).
> Or maybe a truncated fourier series (which is a least squares best fit).
> 
> Another way might be to measure the diameter at many points, but I know that
> there are non-circular forms with constant diameter.
> 
> Suppose I was writing a specification-- how would I specify roundness?  Is
> there some way to just measure it directly?
> 
> I ask this because a friend is making round looking mirror blanks on a jig
> that geometrically should not work.  I want to measure the error of his
> ways.
> 
> Ideas?
> 
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