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

["Jerry" <wa4guu@verizon.net>]

Well... I know exactly what Mutalib is asking. How do you find the "best
center" that would give the largest perfect circle within the not so
perfectly round disk. Then there would be a maximum radius difference of
that largest perfect circle to that point on the edge of the glass at the
maximum distance from the best center.

Let me know what you find out on this Mutalib.

Jerry

-----Original Message-----
From: Dale Eason
 
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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