I am a student at the University of Nevada, Reno and working with Original Piksi RTK Kit (915MHz) and Pixhawk to get precise positioning as reported by the Pixhawk.
My setup consists of Piksi connected to Pixhawk on 4/5 Serial Port and further the Pixhawk is connected to a companion computer (Odroid) via usb cable. The companion computer asks pixhawk about position and based on the location I get, I have to perform some operations. Please note I have followed the getting started guides and I was able to get 3D RTK fix seen on Mission Planner.
According to the Mavlink Message Definitions at [https://pixhawk.ethz.ch/mavlink/#GPS2_RAW] the latitude and longitude calculations start from 10th byte of message #124. I can see the latitude and longitude information but the problem I am facing is the Pixhawk is not showing me correct info. I am off by a couple of miles every time I try to decode the mavlink GPS2_RAW packet. Do I have to do some filtering or bias calculations that will give me correct location?
Here is the whole GPS2_RAW packet I get:
0x18 0x7a 0xd97 0xf0 0x00 0x00 0x00 0x00 0xc6 0x91 0x17 0xc3 0x88 0x95 0xb8 0x70 0x0c 0x15 0x00 0x00 0x00 0x00 0x00 0x60 0x00 0xff 0xff 0x03 0x00 0xa3 0x28 0x05 0x07 0x00
(This packet was captured after I see 3d RTK fix on Mission Planner.)
decoding the latitude : 0x91 0x17 0xc3 0x88 in (WGS84) format I get Latitude : 39.5413699
decoding the longitude: 0x95 0xb8 0x70 0x0c in (WGS84) format I get Longitude : -119.8191504
where as the correct lat long were : 39.546833,-119.832129 as seen on the Piksi Console software.
Is there something I am missing ? Any help regarding this is appreciated.