opencv_traincascade: How are positivies compared during training?

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Dear OpenCV Team and Users,

I wonder how positives are evaluated by opencv_traincascade. Is it required that the cascade returns a hit on each exact positive image, or is it sufficient to hit a subwindow of each positive image? In the latter case: are there parameters to control the maximum deviation, e.g. in scale?

I ask because I have the effect that my trained cascade frequently returns a hit on parts of the objects I want to detect, but not on the entire object.

Can someone point me to the code where the comparison of positives is done during training?

Thanks & best regards,

Michael