MATLAB: How to visualize regionprop object orientation using imshow.

Image Processing Toolboximshoworientationregioprops

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?

Best Answer

y goes downward for images. You'd need
y = c(2) - 10 * sind(props.Orientation);
Related Question