int x = 0;
int y = 0;
int width = 100;
int height = 50;
cv::Rect rect(x, y, width, height);

stringstream bbox;
bbox << "bbox: x = " << rect.x;
bbox << ", y = " << rect.y;
bbox << ", w = " << rect.width;
bbox << ", h = " << rect.height;

rect.area();     // rect的面積
rect.size();     // rect的尺寸 100 × 50
rect.tl();       // 左上頂點座標
rect.br();       // 右下頂點座標 
rect.width();    // rect的寬度
rect.height();   // rect的高度
rect.contains(Point(x, y));  // 查看rect有沒有包含Point(x, y)