Sending hil_gps msg with mavros

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Hello,

I'm trying to build indoor system with ultrasonic sensors. I'm substitute mocap msgs by publishing correct data to /mavros/mocap/pose and /tf , pixhawk accepts it but led won't go in green. So as I understand for flying indoor I also need to give fake gps data? As I undestand I can do it with sending HIL_GPS message. Is it possibly to send this msg with python+mavros? If yes, where I can learn how to do it? Any example?

P.S. I'm not sure but mby its possible to fly indoor without faking gps? If so, can you help me with that?

Thanks in advance, xFirefly