Synthesize Raw GPS

Hi all,

I’m using Pixhawk v1.0 and I wish to send fake GPS data to the Pixhawk.
I searched the forums and saw mentions of fake gps libraries that use alternative data (e.g. vision, sonar) for location approximation.
I wish to completely synthesize GPS data.
This leads to the question:
What fields in GPS_RAW_INT (#24) are mandatory ? How will they affect Pixhawk’s usage of the message data?
for example - can I only send lat and lon data?
In fields where it says “if unknown write XXX”, If I use all those default values, will the data still be used by the Pixhawk?

Thanks in advance.