I had better luck today, but I am now facing some new questions and difficulties
I wanted to test the reliability of establishing a FIX using an NTRIP network for base correction., and compare difference in coordinates that I log. I hoped the separation would be minimal. My NTRI[P service provider is Cansel, which operates the Can-Net network. The intention was to test the reliability of establishing a FIX with the REACH RS mounted on a static tripod, and then using the same REACH RS on a rover pole. Throughout all my tests, I maintained connection with around 15 satellites.
Test 1: Static Tripod configuration was used first. I logged the position using Fix-and-Hold GPS AR mode, and then with Continuous GPS AR Mode. GLONASS AR mode was off in both configurations. The GNSS constellations utilized were GPS, GLONASS and SBAS. Update rate was 5hz in both configurations.
The image below demonstrated the settings used (with GPS AR mod later changed to Continuous):
Using Fix-and-Hold mode, I was able to establish a fix relatively quickly, and the AR Validation ratio quickly climbed to 999.9 I logged the static position 3 times when the AR validation ratio reached 999.9. The logging time as between 1 and 2 minutes for each sample.
Test 2: I switched to Continuous GPS AR Mode, while leaving the reach in the same position. With the exception of this setting, everything else was the same as the configuration in Test 1:
It took considerably longer to establish a fix while in Continuous mode, and the AR Validation ratio did not climb very much past 3. I was able to get a fix, but it did fall out a few times. I logged the position of the REACH RS twice. Each collection lasted between 1 and 2 minutes.
Test 3: Switched back to Fix-and-Hold, without moving the REACH RS. I again surveyed my Static tripod position for between 1 and two minutes. I performed this test in order to compare the first run of Fix-and-Hold points performed in Test 1 to those in Test 3, in order to understand the accuracy of a Fix-and-Hold solution. I hoped to see minimal difference in the recorded positions, given that they were taken at the same location.
Analysis: The difference between the two sets of Fix-and-Hold solutions is unacceptable. Pictured below are two clusters of points. The lower grouping includes the first series of Fix-and-Hold solutions, as well as the Continuous solutions. The upper pair are the second series of Fix-and-Hold (Test 3).
As shown, the difference between the clusters is about .5 m. This difference undermines my trust to perform NTRIP based RTK with the REACH RS in FIX and Hold mode, as I understand it at this point. Given that the location was static, I would expect the results to be much closer. While performing a Kinematic survey with a rover, would the accuracy not be further reduced especially if I am in more rugged terrain or an urban environment?
Next, I looked at the differences in the tighter cluster. The yellow points shown below are the Continuous fix solutions, which are at least close together, separated by only a few millimeters. The grouping of the Fix and hold is also only a few millimeters apart as well.
If these coordinates are reliable, than the spacing in encouraging to using Reach RS with NTRIP to establish a known location, or to survey points. To verify the accuracy, I will next perform this test over a monument with a known position.
Test 4: Kinematic Mode
I next attempted to test the Kinematic Positioning mode. I turned off the REACH RS, attached it to a survey pole, and rebooted and created a new job. I set Positioning to Kinematic and used Fix-and-hold GPS AR mode.
The terrain was quite open, but it is my understanding that Fix and Hold should be used in rugged terrain, or where multipath interference is likely. I hope to use this gear for agriculture purposes, where multipath interference will be present, so I sought to use the setting that seem to be recommended for my actual work conditions.
Now set up with a Rover, and having established a FIX, I surveyed the same spot where my Tripod had previously been set up. The results are seen below, wit the GREEN POINTS showing the supposed location I surveyed with the ROVER pole.
This is a full Metre from the position given it Continuous and Static mode, and near the same difference from the Second sample (Test 3) using Fix and Hold. Given that I want to use this system with Real Time corrections applied, these differences are discouraging. In my experience with other stand alone systems using a rover and NTRIP network to supply the base, I needed to calibrate myself on site. Granted, in this case I was using a local coordinate system and associated datum, rather than simply using the WGS84 information from the GNSS network that Reach RS, so I am not sure if calibration is something that can be forgone. Can-Sel provides an adequate summary of the process involved in calibration, which is basically what I followed by tying into local monuments. The system I used in that case gave me a real time position the local coordinate system, which I could see was off from the monument position until I performed an inverse solution based (I hope my explanation makes sense here, as I was shown how to do this in a n ad hoc manner)
http://www.can-net.ca/index.php?option=com_content&view=article&id=32&Itemid=74&lang=en
Anyway, I would like to know if I am out to lunch on this stuff.
How do I improve consistency in my surveyed points?
What sort of tests can I perform to ensure the coordinates I log can be used as a base position in the future?
Is there perhaps a compatibility problem with the NTRIP provider and REACH RS?
How can I determine whether I can trust the results from Fix and Hold or Continuous (setting up over a monument is my next step).
Thanks.
