I am trying to detect near-vertical lines in an image using ippiHoughLine_Region_8u32f_C1R.
The documentation doesn't define theta, but it is apparently the angle of the normal to the line, relative to horizontal. So a vertical line in the image would be 0 radians, and as that line rotated counter-clockwise the angle increases.
The function is working for me for lines that are vertical or positive theta. But I can't get the correct angle for a line that is near-vertical but sloped the other way (slighly clockwise of 0), what would normally be negative theta. Regardless of the range parameters I specify (for some reason named dstRoi in the arguments), I cannot get the angle to be found correctly. The angle theta is always small and positive, as if it is reflected about the origin. I expect theta to either be a small negative number, or close to 2*PI.
This seems to be a bug in the function, or am I doing something wrong?