How do I draw a line along the major axis as found with regionprops

I have used the regionprops to find the MajorAxisLenth of each object in my image. How do I draw a line along the major axis?

Answer 1

[Walter Roberson]

If you get the Centroid and Orientation and MajorAxisLength properties, then this becomes mostly a traditional y = m*x + b problem, where m is tan() of the Orientation and b is chosen so that the line passes through the Centroid.

Or even easier, MajorAxisLength * cosd(Orientation) to get the x axis coordinate difference, center that around the Centroid, likewise MajorAxisLength * sind(Orientation) to get the y coordinate difference, center that around the Centroid; then line() between the two endpoints.

[Pooja lepcha]

How do I get the other points meaning the x and y co-ordinates of the ends of the major axis on the object?

[Eric T]

Pooja: say you have deltax and deltay, and centroid coordinate is x,y. Then the line ends are:

xVals=[x-deltax/2 x+deltax/2]

yVals=[y-deltay/2 y+deltay/2]

line(xVals,yVals) will plot the line.

[Abhinav Agarwal]

What is delta x and delta y?

[Image Analyst]

It's the width of the bounding box.

Now they have bwferet() so look into that.

Answer 2

[Doug Hull]

This is somewhat similar.

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