AusPos or RTKPost?

[RoryG (Rory Gillies)]

We have a network of five permanent markers across Shetland so we can use a RS2 base and NTRIP and never have a baseline more than 25km to the rover.

I was using one of the marks the other day and as always set logging in case I needed to PPK any points (areas without mobile data). As a test I submitted the observations to AusPos then converted from ITRF2014 to ETRF89 then to OSGB36. The position uncertainty for the AusPos rapid solution was 0.006E 0.007N 0.026H shown below as OSGB36:

445705.661E 1141458.721N 106.160H

Processing in RTKPost using observations from the National Reference Station less than 2km away we get (again converted to OSGB36):

445705.593E 1141458.766N 106.110H

That’s a difference of:

0.068E -0.045N 0.050H

The RTKPost solution was less than 0.010m ENH from the coordinates we use, so which is likely to be the most accurate? Given AusPos uses GPS only and the RTKPost solution uses GPS and GLONASS I would be inclined to go with our solution. Any thoughts?

I’ll submit the observations to AusPos again in a couple of weeks to get a final solution and see if it’s any nearer the RTKPost solution with the receiver nav files.

[kseniia.suzdaltseva]

Hi Rory,

The specificity of the PPK and PPP technologies is that the highest accuracy they provide is centimeter-level. The coordinates you collected are very similar, so they both look reliable.

You can conduct tests with known marks to say which method’s results are closer to the truth. Also, let’s wait for a while to see how the PPP result changes when you use the Final ephemeris.

Note that the datum transformations can play their part and slightly distort the results.

Given AusPos uses GPS only and the RTKPost solution uses GPS and GLONASS I would be inclined to go with our solution.

The number of the GNSS used indeed affects the solution calculation. Still, if your receiver gets enough GPS signals and collects the log relatively long, PPP can give a very accurate point position using only GPS.