In the description of cv::HoughLines it says
Output vector of lines. Each line is represented by a two-element vector (ρ,θ) . ρ is the distance from the coordinate origin (0,0) (top-left corner of the image). θ is the line rotation angle in radians ( 0∼vertical line,π/2∼horizontal line ).
So what is the return type? Is it a Nx1 CV??C2 or Nx2 CV??C1? The line roate clockwise or anticlockwise? which direction would a π/2 line points to?
Hopefully someone can wirte a better documentation so the rest the programmer know how to use it right away.