I have a sparkfun express plus with the u-blox zed 9r chip in it. I’ve been logging data in u-center via usb and the config ublox port. The z data is known not to be that accurate, however it mirrors the x data in a linear fashion without altitude change . Below id just a sample of the deltas on y & z, and I have multiple data sets where there is a linear relationship between them.
y z
0 0.01
-0.02 0
-0.03 0.02
0.32 0.35
0.38 0.4
0.46 0.48
0.49 0.54
0.42 0.44
0.53 0.57
0.68 0.73
0.84 0.9
0.82 0.87
0.82 0.87
0.85 0.89
0.8 0.88
0.84 0.9
That should be Y & Z ! :roll:
Hi,
I think this is due to the ECEF coordinate system being 3D?
The “rule of thumb” is that height / altitude is twice as inaccurate as latitude and longitude. That’s because there are no satellites ‘below’ you when calculating the height.
Think about sailing East-West along the equator. In Latitude, Longitude, Height coordinates, only the Longitude is changing. The Latitude and Height are constant. But in Earth Centered Earth Fixed coordinates, both X and Y are changing. Only Z is constant.
Likewise, if you sail due North, only your Latitude changes. Longitude and Height are constant. But in ECEF, it is complicated. If you are on the Prime Meridian (0 degrees Longitude), X and Z are changing. Y is constant. But if you did the same thing at 90 or 270 degrees Longitude, then Y and Z would change. X would be constant.
I think this explains what you are seeing?
The chart from u-center is velocity in Z and Y (VZ and VY in meters per second). The effect will depend on where you are and your antenna’s view of the sky. If the satellite signals are reflected off surrounding buildings, that really complicates things…
Best wishes,
Paul
This path was pretty much due north for about 38m then back south , then about 285 W / E , both 3 times. Nothing to obstruct or reflect, rtk base mounted in my back yard. N/S has less than a 1m drop. W/E no altitude. Doesn’t matter the path, they basically act like that anywhere.
