How to visualize MajorAxisLength and MinorAxisLength on images?

Hi,

I would like to replicate something similar to that shown in the explanation of "Orientation" property of the "regionprops" function, as viewable here:

http://it.mathworks.com/help/images/ref/regionprops.html

I would plot the red ellipse and the blue lines representing the axes, over my images (both binary and grayscale). I found this example:

http://blogs.mathworks.com/steve/2010/07/30/visualizing-regionprops-ellipse-measurements/

but I can't understand how complete the code to plot the blue lines. Could anyone help me, please?

Thanks for your answers.

Answer 1

[Image Analyst]

Get the two endpoints of the line, then call plot. For example x1 = xCentroid + (majorAxisLength/2) * cosd(orientation). Same for y1, x2,and y2. It's just simple trigonometry. Then call plot([x1,x2], [y1,y2], 'r-').

[Image Analyst]

Note that the ends/tips of the major axis don't usually lie on the perimeter. If you want/need that, see my attached demo.

[Nut]

You're right, it was very simple but I didn't see the solution, I don't know why!

About the ends of the axis, I already know they don't usually lie on the perimeter, but it is not an issue in my work, I have not to plot the axes so precisely. Anyway, your demo is very interesting, I'll keep and try it.

Thank you very much!

[hu]

Is it possible to modify the code so I can see how to run it on image contain several objects (like rice.png)?

Thanks a lot.

[Image Analyst]

See Steve's blog: https://blogs.mathworks.com/steve/2010/07/30/visualizing-regionprops-ellipse-measurements/