Pixhawk with FAKEGPS

Recently I just want to use fake gps signal to make the drone fix indoors in Loiter mode with Pixhawk. ( I programed to convert the UWB xyz position info to NMEA protocol and pluged in gps port )

Now the drone can fix in one position, but it still drifts, not that still. (Following is the test log link), The error on mission planner like Error pos horiz variance often happens.
#Does anyone encounter these problems? I really hope someone could help me~~

https://drive.google.com/open?id=0B1XJyGUjIacXdW9OdWtMb21UOHc

This was appearing as a blog post so I’ve modified the category.
If you don’t get a response you might want to check in the VisionProject gitter chat room.