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

[Dale Eason <atmpob@yahoo.com>]

The definition of a circle is all points equal radius
from a point.  Thus any diameter should be the same
within a tolerance you pick and can measure.

I know of no other geometry that has that attribute. 
Can you give me one?

Dale Eason


--- Mutalib Abdallah <omegatroid@hotmail.com> 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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