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lines in cv::HoughLines typically returns a N x 1 32F C2 Mat,N is the number of lines identified.Channel 1 which is named ρ and took the range between(-∞，+∞)represent the minimum distance beween the line and the origin.Channel 2 which is named θ represents the direction of the line relative to the orign and took and range of [0,π).At θ=0 the line will be vertically points to y+ (imagine line has direction, in Mat or image y+ is downwards) if the origin is on the RHS of the line ρ will be positive else will be negtive.As θ increase the line roates and shifts clockwise until it reachs θ=π¯ which is a vertically line points upwards.

Still a bit of wordy and not very intuitive.