Thread Subject: smoothing

Hey all..

I have coordinate points for an image. I know the general shape I get if I connect the points is a parabola. Can anyone tell me how to smooth the curve out (since the number of points are less). I tried using SPLINE...didnt work...Any other methods????

Thanks for any help in advance...

Matt

Dear Mathew!

> I have coordinate points for an image. I know the general shape I get if I connect the points is a parabola. Can anyone tell me how to smooth the curve out (since the number of points are less). I tried using SPLINE...didnt work...Any other methods????

Please define "smooth" and "didn't work".
Jan

"Mathew Thomas" <mathew99@gmail.com> wrote in message <heamlh$81c$1@fred.mathworks.com>...
> Hey all..
>
> I have coordinate points for an image. I know the general shape I get if I connect the points is a parabola. Can anyone tell me how to smooth the curve out (since the number of points are less). I tried using SPLINE...didnt work...Any other methods????
>
> Thanks for any help in advance...
>
> Matt

Hi Matt.

If I understand your question well, your problem is rather simple. The equation of (quadratic) parabola is f(x) = c1*x^2 +c2*x + c3. I should be an approximation of measured points y(x). The unknowns coefficients of f(x) may be obtained by the following code:

x = x(:);
c = [x.^2, x, ones(size(x))] \ y(:);

Hope it helps.
Mira

"Miroslav Balda" <miroslav.nospam@balda.cz> wrote in message <heb8hd$p9j$1@fred.mathworks.com>...
> "Mathew Thomas" <mathew99@gmail.com> wrote in message <heamlh$81c$1@fred.mathworks.com>...
> > Hey all..
> >
> > I have coordinate points for an image. I know the general shape I get if I connect the points is a parabola. Can anyone tell me how to smooth the curve out (since the number of points are less). I tried using SPLINE...didnt work...Any other methods????
> >
> > Thanks for any help in advance...
> >
> > Matt
>
> Hi Matt.
>
> If I understand your question well, your problem is rather simple. The equation of (quadratic) parabola is f(x) = c1*x^2 +c2*x + c3. I should be an approximation of measured points y(x). The unknowns coefficients of f(x) may be obtained by the following code:
>
> x = x(:);
> c = [x.^2, x, ones(size(x))] \ y(:);

Or by using

c=polyfit(x,y,2);

which has some beefed up measures to handle numerical issues.

"Miroslav Balda" <miroslav.nospam@balda.cz> wrote in message <heb8hd$p9j$1@fred.mathworks.com>...
> "Mathew Thomas" <mathew99@gmail.com> wrote in message <heamlh$81c$1@fred.mathworks.com>...
> > Hey all..
> >
> > I have coordinate points for an image. I know the general shape I get if I connect the points is a parabola. Can anyone tell me how to smooth the curve out (since the number of points are less). I tried using SPLINE...didnt work...Any other methods????
> >
> > Thanks for any help in advance...
> >
> > Matt
>
> Hi Matt.
>
> If I understand your question well, your problem is rather simple. The equation of (quadratic) parabola is f(x) = c1*x^2 +c2*x + c3. I should be an approximation of measured points y(x). The unknowns coefficients of f(x) may be obtained by the following code:
>
> x = x(:);
> c = [x.^2, x, ones(size(x))] \ y(:);
>
> Hope it helps.
> Mira

Thank you soo much...About to try it out right now...

"Jan Simon" <matlab.THIS_YEAR@nMINUSsimon.de> wrote in message <heb8fd$l8t$1@fred.mathworks.com>...
> Dear Mathew!
>
> > I have coordinate points for an image. I know the general shape I get if I connect the points is a parabola. Can anyone tell me how to smooth the curve out (since the number of points are less). I tried using SPLINE...didnt work...Any other methods????
>
> Please define "smooth" and "didn't work".
> Jan

Hey Jan,

I meant the points are being connected as a straight line...and I want it curved...When all the points are connected, it should more or less have a parabolic shape...

Thanks.

Dear Mathew!

> I meant the points are being connected as a straight line...and I want it curved...When all the points are connected, it should more or less have a parabolic shape...

With the above mentioned POLYFIT, you can get even an exact parabolic shape.

Good luck, Jan