I setup the antenna and have started logging. I note something very strange:
With just the faucet I get the location almost spot on (100mm) and on google maps it shows the correct location.
The reference station is reporting it’s location almost exactly 3m North of it’s true location (+/- the error), East/West is correct.
When I use the faucet with the correction data from the reference station it is then also 3m North.
The question is why 3m North? Is there an offset setting? If the faucet and my phone’s GPS are returning more accurate location data than the reference station what could be going on?
I understand I will set the location of the reference station with PPP but the currant location error is above my expectation given that even my phone is more accurate.
Is the Reference Station in “Base” mode? Has it completed its Survey-In? I wonder if you moved the antenna while the Survey-In was already running, causing the offset?
No it was in Rover because I read this was what I should use while collecting for PPP. I just downloaded the ubx file and loaded it into u-center (v1). I have attached the deviation and altitude plot and as you can see sudden jumps in the positional data. The antenna is fixed in its permanent position on the roof of my house so No it did not move. I am still not sure the position is accurate but it could be a map error as it looks about 50cm off to me. I am just wandering why the jumps and I am hoping after getting it’s final position from CSRS-PPP this error will fix itself (I hope). As an added test I took the faucet down to the sea (with NTRIP connected, about 100m away) to get an altitude and It reported -1m height. Something just does not stick with me as it feels wrong so I am looking for ideas to fix/understand why.
I worked it out, I must have had a short power cut (common where I installed it) and the Reference Station then restarted in Base mode. It’s the only logical answer after eliminating everything else. I confirmed this as I had multiple log files on the SD card when there should have been one. Once in Base mode it maintained it’s location and altitude for as long as possible as a static reference to provide relative location data. I reset it again today to start collecting data and hope no power cuts for the next 2 days
Survey-In is not particularly reliable, unaided it’s prone to have the same CEP type numbers as regular GPS/GNSS, you just tend to average the inherent biases.
Where this is the only method available, I’d tend to record and stick with one set of values. Perhaps have software record and log the position at a given location, and snap the static location to the prior one so there is consistency between visits.
Does assume you have a hard-mount antenna fixture at the location so you’re surveying the same spot.
Around here contractors use a mix of iron pipe, fittings, and 5/8" bolts to establish locations of key fence posts or poles.
From what I found out Survey-In is problematic because as the Sats come in and out of view. The base station then recalculates it’s position, you can see the jumps in altitude from the attached image. As the rover is relative to the base if by any chance the base recalculates it’s location (a) you would not know because the rover gets corrections and (b) your marks will just move during the survey.
If you are in base mode this recalculation should not/never happen as is shown in the picture (but his might be inevitable). I agree that once the Survey-In is completed at the start the location should be recorded and the position marked then verify at the end too.
As for the logging data that I collected I was surprised that the data I collected in base mode was good when I sent it to CSRS-PPP for processing it gave 2mm accuracy. As I did not trust this original data I re-logged the data in rover mode to compare and the location came back the same +/- 2mm. This means the GPS coordinates in base mode has little effect on determining an accurate location!! Or in base mode the data logged was RAW (I think this option) and CSRS-PPP use this RAW data.
Just for addition information I also found you get better accuracy in low humidity conditions and this shown in my data too.
You are Right, while the ZEP is logging raw data in the correct setting, it doesn’t really matter if the unit is in base or rover,
but Having 2 units, one acting as a base is the way to go. You can survey a land/property in RTK mode, and latter at the office correct your base position. there fore all your collected data ill be accurate talking about absolute position.
Another example. There are times when you can’t have a bridge to communicate your 2 units in real time, In that scenario, log raw data at your base and also in your rover, making both units log at the same time. Later that, when you correct your base, you can correct all your logged points with with the rover with a post processing software, and you will be amazed by the precision you can achieve.
