How to visualize regionprop object orientation using imshow.

I would like to plot a line along the major axis of an object. For example, given:

A = [ 0     0     0     0     0;
      0     0     0     0     0;
      0     0     1     0     0;
      0     1     0     0     0;
      0     0     0     0     0;];
imshow(A); hold on;

props = regionprops(A,'Orientation','Centroid');
c = props.Centroid;

Creates an image with an object that has a major axis at 45 degrees to the X axis. Regioprops agrees:

>> props.Orientation

ans =

      45

If I understand my trigonometry:

x = c(1) + 10 * cosd(props.Orientation);
y = c(2) + 10 * sind(props.Orientation);
line([c(1) x],[c(2) y])

should produce a line along the Major Axis of the object. Instead it produces a line perpendicular to the major axis. Why is the line not along the Major Axis of the object?

Answer 1

[Image Analyst]

y goes downward for images. You'd need

y = c(2) - 10 * sind(props.Orientation);

[Animesh Biswas]

Hi,

I have a follow up question here. I would want to plot many orientation (line as mentioned above) of an object with color gradient, or with different colors. Please suggest how can I do that.

Thank you

[Image Analyst]

Not sure what you want. Maybe you could use markers with plot() if the line needs a color gradient along the line, or maybe you could specify 'Color' in line(). Show a screen mockup of what you want.