curvature calculation

[SUSIE]

I have an image smoothed using Gaussian smoothing technique. The edges of the object in this image has been detected. Next, i would like to calculate the curavture of the edges. How can do so using Matlab 6 ? thanks.

 

[Sonya]

you might try using a function like polyfit in matlab to fit a polynomial of whatever degree you find appropriate to your edge, or parts of it. from the function that is returned to you, you can analytically compute the curvature.

hope this is useful.

Sonya

 

[SUSIE]

Hello,

thanks for the reply. I had actually tried using polyfit to do so. But the problem is : there are multiple points occur with the same x or with the same y. So, how can i eliminate this ?? thanks

 

[joe3]

Hi,
1)Use contour to get contineous lines.
2) Find turning points by chacking sign(diff(x)) for each line and split it to single valued lines.

Joe
BSTEX - Equation viewer for Matlab

http://www.geocities.com/bstex2001

 

[SUSIE]

Hello,

There are a lot of circular objects which are the objects of my interest. So, I dun think using contour can help me to draw the the continuoes line for all the circular objects where some are connected and others are not. Moreover, I really don't know how many line i need to draw.

I am actually thinking whether i can just count the curvature at each of the edge point that i found from the Canny Edge Detector method. Is there any way for me to do so ?? Thanks.

 

[joe3]

Hi,
Sure you can do it because any 3 points defines a unique circle that its radius can be associated with the curvature at the mid point. This is a simple Euclidian geometry. The only thing is that:
1) You have to make sure that any point has only 2 neighbors (use 'thin'), and to check nearest neighbors.
2) The result will be very 'noisy'.(You may try to smooth the curvature result after computation.

Joe
BSTEX - Equation viewer for Matlab

http://www.geocities.com/bstex2001

 

[SUSIE]

Hello,

If i do have any preliminary knowledge on the radius of the circular objects, is there any way for me to calculate the curvature at the edge point ? thanks

 

[SUSIE]

Hello,

If i do NOT have any preliminary knowledge on the radius of the circular objects, is there any way for me to calculate the curvature at the edge point ? thanks