While working with 2D transformations and ellipses I painfully found out that the orientation of the angle in ellipse and getRotationMatrix2D is different. What is the reason for this inconsistency?
The ellipse angle is positive in clockwise direction:
The getRotationMatrix2D angle orientation is described as Positive values mean counter-clockwise rotation (the coordinate origin is assumed to be the top-left corner).
I assume that the coordinate system origin is in all OpenCV functions in the top-left corner, which is standard when working with images.