Re: Template Matching with Rotation ?

Posted by Ronald Michaels on May 14, 2010; 2:06pm
URL: http://imagej.273.s1.nabble.com/Template-Matching-with-Rotation-tp3688295p3688296.html

Is there a simple way to detect rotated shapes ?

Hi -

In concept, yes.

Disclaimer:  I work with convolution in the x,y coordinate system and I have no direct experience with r, theta systems.

In x,y coordinates, convolution will find the similar shaped (and oriented) object anywhere in the x, y coordinates of the image.  Convolution using r, theta coordinates should find a similar object anywhere along the theta axis.

Here is a possible route to a solution.  Convert the "certain shape" and the object in question to r, theta coordinates.  The r, theta origin should be at some definable, repeatable point like center of mass of the shape.  Convolve the images using the Convolution Theorem.  The result should have a response at the angle of rotation of the object in question.

I suspect that the hard part may be finding the location and center point of the individual shapes.

Perhaps someone more familiar with ImageJ plugins may be able to suggest a computational route within ImageJ.  I personally would use a Math package like Scilab for this problem.

Best wishes

Ron