Traffic light Detection Question

[EcotronCorp]

What is the reason for adding M_PI_2 when calculating the tl_yaw angle of traffic lights in traffic_light_map_based_detector? After the range screening is completed, the angle value obtained for different traffic lights is always a fixed value of 1.57079. When there is a traffic light in front of the vehicle, but the difference between the angle between the camera and the traffic light is greater than 40 degrees, it will not be selected as a possible traffic light to be detected.