Opencv. LBP cascade. How to exclude redected results at the same place

edit

I have trained LBP classifier for searching cars top view. And i do not know how to exlude redetection at the same places during searching.

I saved a resulting picture, as you see one car is found twice:

I use this function:

cascade.detectMultiScale( smallImg, cars,
    1.1, 3, 0
    //|CV_HAAR_FIND_BIGGEST_OBJECT
    //|CV_HAAR_DO_ROUGH_SEARCH
    |CV_HAAR_SCALE_IMAGE
    ,
    Size(30, 30),
    Size(700,700)
    );