Clear Filters
Clear Filters

ellipses on image

3 views (last 30 days)
thoraya on 20 Jun 2012
hi; I have a set of ellipses where each ellipse is defined by its center position (x,y) , an orientaion angle teta, major axe a and a minor axe b. i want to find a way in order to draw those ellipses on a given image* Img* . any idea please? thank you
  1 Comment
Image Analyst
Image Analyst on 8 Jul 2012
"Burn" it into the image pixels, or just display above the image in the overlay (without changing image pixel values at all)?

Sign in to comment.

Answers (2)

Walter Roberson
Walter Roberson on 8 Jul 2012
One way is to calculate a circle such as is described in the FAQ. Make it a unit circle as you first calculate it. Multiply the x coordinates by (a/2) and the y coordinates by (b/2). Then use hgtransform() to rotate it around the angle. Finally, add the center coordinates to the transformed results.
Richard Brown
Richard Brown on 9 Jul 2012
Sorry, didn't read the question properly:
phi = linspace(0, 2*pi, 100);
Q = [cos(theta), -sin(theta); sin(theta), cos(theta)];
X = bsxfun(@plus, [xc; yc], Q * [a/2 * cos(phi); b/2 * sin(phi)]);
plot(X(1, :), X(2, :))
... yes, your way may be cleaner :)
Walter Roberson
Walter Roberson on 9 Jul 2012
I have no objection to using a rotation matrix instead of hgtransform() :-)

Sign in to comment.

Ryan on 9 Jul 2012
Edited: Ryan on 9 Jul 2012
Use pdeellip (if you have the PDE toolbox):
(xc,yc) = centroid
(a,b) = semiaxes
phi = rotation of ellipse


Find more on Animation in Help Center and File Exchange


Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!