Thread Subject: How to find normal distance between two curves from one point in a curve?

I have two continuous curves for which I have only the data points. Both curves approx. look like a semi-circle (though not a semi-circle). From a known point on one of the curves, I want to find the NORMAL distance (not smallest distance) to the other curve.
      The data points are closely spaced. So what I planned to do was to find the normal at the said point (say A)(lying on curve 1) and find the point of intersection of the normal and the other curve (curve 2).

I have found the slope of normal at the point by using the point A by using the two points adjacent to it. But how to find the point of intersection?

Thanks.

Vinay

"Vinaykumar " <vin1009@yahoo.com> wrote in message
news:he7ug5$k3v$1@fred.mathworks.com...
>I have two continuous curves for which I have only the data points. Both
>curves approx. look like a semi-circle (though not a semi-circle). From a
>known point on one of the curves, I want to find the NORMAL distance (not
>smallest distance) to the other curve.
> The data points are closely spaced. So what I planned to do was to
> find the normal at the said point (say A)(lying on curve 1) and find the
> point of intersection of the normal and the other curve (curve 2).
>
> I have found the slope of normal at the point by using the point A by
> using the two points adjacent to it. But how to find the point of
> intersection?
>
> Thanks.
>
> Vinay

may be one suggestion:

can't you just fit a curve (polynomial) to the few points around A? then
find its derivative at A, this gives you the slope s of the tangent at A,
then slope of normal is -1/s, then you have the line equation of the normal
line (slope + coordinates of point A i.e. y-y1=slope*(x-x1) ), then find
intersection of this line with the other curve equation (which you also
would fit to a curve, so you have its equation). solving the 2 equations for
the intersection point?

--Nasser

"Vinaykumar " <vin1009@yahoo.com> wrote in message <he7ug5$k3v$1@fred.mathworks.com>...

>
> I have found the slope of normal at the point by using the point A by using the two points adjacent to it. But how to find the point of intersection?

Just writing down both the segment and the normal lines in parametric form. The intersection condition provides a a 2 x 2 linear system, which can be solved it using backslash.

Bruno