Problems when using hil gps

Hello . I am using raspberry to send gps information to pixhawk( I am using a gps card which is not officially supportted) . pixhawk could get all the values except eph and epv data . And I don’t know what caused this problem? I trid to change mavlink_receiver.cpp and give hil_gps.eph a fixed value , but I still get value 0 from qgroundcontrol