SMARTNAV L1 RTK field test results, as promised. Please have a look at this previous post before reading.
The reference trajectory will be displayed in dark blue whereas SMARTNAV's output will be displayed as :
- red for "single" solutions (when RTK is not available)
- yellow for "float" solutions
- green for "fix" solutions (maximum accuracy)
So first we will review all the points listed in the previous post.
It is common knowledge that GNSS tend to output poor vertical position accuracy due to the low vertical spacing of satellites. We wanted to check whether RTK could enhance this.
Standard deviation is about 4 meters. This is not bad considering the "low VDOP" of satellites and the measurement conditions.
The idea behind this test was to monitor how receiver would deal with successive acquisitions/losses of satellites.
Receivers loses lock completely under bridges and tunnels. Reacquisition is quite fast and even if there are some glitches convergence is fast.
The trajectory is very good here, due to the open sky view. But it is difficult to measure repeatability under those conditions.
The most difficult environment, really small roads with high buildings.
Here the output is not correct at all. The receiver has a hard time calculating the solution. Even the reference trajectory is not precise at all. This is normal considering the conditions, glitches go up to hundreds of meters.
We wanted to know whether trees affect position stability or not.
At the moment we drove under the trees, they were masking the sky completely. We can easily see that solution is not robust in this kind of area.
Repeatability was difficult to measure with the car, because it is difficult to make sure to follow the same path several times in an urban area. So we did another test. SMARTNAV was placed on a square table, calculating real-time RTK solutions. Baseline was about 10 meters. SMARTNAV was moved around table's edge several times, always following the same path.
It is very easy to reproduce the same path. Here the accuracy is under 5 cm.
In open sky conditions, accuracy is always better than 20 cm.
However, when conditions are difficult, offsets as high as 1 meter can be observed. Offsets tend to appear after a glitch is observed. A time of convergence shows up after a glitch to come back to the reference trajectory.
In stationary, this is the position calculated by SMARTNAV.
This is the position calculated by L1/L2 AsteRx (without inertial hybridation).
There does not seem to be much precision difference between the two.
NRTK (SMARTNAV real time) availability :
- Fix : 27%
- Float : 62.5%
- Single : 10.5%
L1/L2 (post-processed) availability :
- Fix : 50.6%
- Float : 46.1%
- Single : 3.2%
L1/L2 is much more available than L1, which means it will be more robust in difficult environments or longer baselines.
- RTK in urban areas is not a pipe dream
- reacquisitions are fast
- excellent precision/accuracy in open sky views
- still quite strong in "medium" environments (could be enhanced by hybridation with an IMU or a better software cycle slip detection)
- not reliable when sky view is heavily obstructed
- L1/L2 does not look more precise than L1, but it is more robust and available