How to get estimated global coords without GPS

Hi all,

I use Arducopter at Pixhawk without GPS sensor. I have set EKF3 origin coordinates with mavlink message SET_GPS_GLOBAL_ORIGIN and origin coordinates are reflected correctly in message GLOBAL_POSITION_INT, which I receive from Pixhawk.

But when I move my copter (no difference armed or not) down the street, I don’t see any change in estimated GPS coordinates in mavlink message GLOBAL_POSITION_INT. Yes, there are no GPS sensor, but IMU should fix movements, isn’t it?

How to get estimated GPS coordinates? May be some mavlink message, may be pixhawk logs, any source would be fine. I know, IMU is completely not enough to get correct coordinates, but I have improved IMU and I need to know how many seconds I can rely on it without GPS signal. How many seconds I will get correct coordinates without GPS.

Please help, friends. I have wasted more than week trying to resolve this issue. Any help will be very appreciated. Thank you!