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# Coordinates between two antennas

Q&A forumCategory: QuestionsCoordinates between two antennas

Hi,
I am using simpleRTK2B+heading modules to get an accurate heading on my robot, so I have two antennas on it.
Is there a way to get the GPS coordinates of the point in between the two antennas (midway) ?

Hello,
If I understood well you want to compute the middle point coordinates (Xm, Ym, Zm) of the 3D straight line segment between the two antennas. If the coordinates of the first antenna are (X1, Y1, Z1) and the coordinates of the other antenna is (X2, Y2, Z2), then the middle point coordinates are:
Xm = (X1+X2)/2
Ym = (Y1+Y2)/2
Zm = (Z1+Z2)/2

If you know the reported position of each antenna, and the distance is short (1-2m) couldn’t you just use simple geometry?
For a relative NED value the parameters would simply halve.
In the ECEF frame, find the average and convert that to LLH, the math would be heavier, and wouldn’t likely yield any higher useable precision.

thanks for your answer, but I don’t know the GPS coordinates of each antenna. I’m using UBX messages and I find GPS coordinates for only one of my antenna.

Missing a trick there then. Pulling PVT+NED from the secondary receiver is going to give the most noisy/fragile solution.

If you only have one set of coordinates, you’d probably want to place “that” antenna over the turning center of the vehicle, often that is above the centre lines of the rear fixed axle. Figure out where the front of the vehicle is from your own measurements, and the angle it is pointing.