2-Reach RS2 Workflow Check

[j.r (Jacob R)]

Hello everybody,

After reviewing the Docs and Forum, I still have a little brain fog over a proper workflow utilizing two Reach RS2 (one as the base and one as the rover) and the PPK process. I would greatly appreciate a confirmation, correction, or a redirect to an appropriate process. I will be receiving two demo units in a couple of weeks to experiment with and I want to “hit the ground running” to make the most of the 3-day lease.

Background:
I work in a river authority and help manage a sewer pipeline transmission system covering hundreds of square miles. We routinely collect data points for manholes, siphons, meters, etc. This data is used by a GIS system for numerous applications. Currently our survey instruments use an RTK solution - which can be accurate to 4 inches - and require only a 20 second gathering time per survey point.

Objective:
I want to implement the Reach RS2 with a PPK solution to improve accuracy and increase the number of survey instruments available to my workers.

Current Workflow Understanding

1. Setup one receiver over an unknown point.
2. Set to base mode and begin raw data logging.
3. Use average single to receive a placeholder coordinate for the base.
4. In corrections output, turn on LoRa radio (will be working in line of sight).
5. Setup other receiver as the rover.
6. In corrections input, turn on LoRa radio and tune to the base station.
7. Setup new survey in the app and log points for 20 - 60 seconds. Repeat for each point.
8. Turn off rover unit.
9. Stop raw logging in the base unit and then shut it down.
   Note: Ideally, my guys would do this in about 15 minutes. Is that feasible?
10. Return to the office and extract logs.
11. Process base and rover logs using data from the nearby CORS station and calculate an absolute base station coordinate.
12. Correct the rover units using the corrected base station coordinate as a reference.
13. End up with cm accurate, absolute points for the GIS system.

Conclusion
This is my current understanding in a nutshell. Is this workflow correct? Did I miss anything? Are my expectations reasonable? If I misunderstood anything, what is the appropriate solution? Thank you in advance for the help and apologies for the long post!

[TB_RTK]

Congratulation on your decision. RS2 is really bang for the buck.

For the answers below i assume you have a LoRa RTK or some other connection to the rover giving you a RTK session. PPK is something els and you dont need LoRa for that.

@j.r

Setup new survey in the app and log points for 20 - 60 seconds. Repeat for each point.

This point (7). For confirmation i would rather pick a 2-5 second collection time (ok rms) and if the point is crucial, resurvey this point one or two more time with minimum of 20min apart with the same 2-5sec iteration.
The longevity of collection time doesnt do you any good in the case. Either you have fix or you dont. If you have fix the next question would be if the fix is good or fals, you cant verify that with a 20-60sec session.

For PPK you really dont know if you have a FIX or not in e.g a manhole as your workflow is collecting raw log from rover and base and process them later, NOT in real time like RTK.

It sounds like you should use RTK with correction obtained via LoRa or NTRIP over internet/ethernet

#my2cent

[j.r (Jacob R)]

@TB_RTK Thanks for your quick reply! Some more explanation is due to you:

@TB_RTK

For the answers below i assume you have a LoRa RTK or some other connection to the rover giving you a RTK session. PPK is something els and you dont need LoRa for that.

Maybe my understanding of PPK and RTK is still muddled. I want the baseline measurement to be accurate (thus utilizing the LoRa radio). So the relative positions is corrected in real time (RTK) but to receive the correct absolute position, I would need to post process the base station with a CORS station. Now the rover points will be translated to same amount as the base station and result with correct absolute points. Is this correct?

@TB_RTK

Either you have fix or you dont.

Fix meaning good connection with the satellites?

[tracy.love]

your on the right track, once you get the receivers it will make more sense.

“Use average single to receive a placeholder coordinate for the base.”
<write down your resulting X,Y,Z>
then begin a raw file for the base
then turn on lora

if you turn on raw logging for the rover then you can post process (PPK) the rover file against the base station but the result will be a very accurate track file as your “events” (here is a manhole cover) are not represented in the raw file, only in your rover survey file.

afterwards you will need to post process as static the base raw file against a CORS station. this will tell you where you really were. i then use a tool in my desktop GIS to shift the rover points to match.

I currently log base and rover files and do PPK even if i have a day where its all great RTK fixes. the PPK in this case provides a check on my RTK work to make sure i didnt get any false fixes.

[conehead (Chris)]

As Tracy mentioned you will need to enable logging of raw data on the Rover as well as the base to run PPK. Correcting the base position can be done with PPK using a nearby (<100km) reference station (CORS or other) or with PPP by submitting the Base RINEX log to an online PPP service. Either way to perform PPK on your Rover locations you will need a corrected Base position and raw logs for both Base and Rover. Also good practice to perform some observations at known survey monuments within the area of interest.

[TB_RTK]

Sorry, it was late Friday night and I see the beer didnt help me at all.

First of, in your line of work deep down manholes and what nots I am guessing you would be facing the same issues I have, getting FIX.
Working deep in a trench and so on is really pushing the limits. You would pretty much have the sky blocked or most of it and powercables running close by doesnt help at all.

I would do the survey in RTK mode (yes, you will have raw logging on base and rover too). Rover relative to your base.
RTK feeds you live solution of your plot, either a SINGEL, FLOAT or as a FIX status, this will give you a indication if surveying a point is doable or not. I am assuming this step is clear, right?

@j.r

Now the rover points will be translated to same amount as the base station and result with correct absolute points. Is this correct?

Raw data from base can not be processed with data from the survey menu (exported geojson, csv etc). You need raw or rinex files from the logging menu on both rover and base.

Now, if you do your survey with a unknown base station and you dont have any known points or anything nearby to work of, there are few ways to solve that. Also assuming the end goal is absolute positions of all your points.

PPP. Process base data with NrCan. Depending on the accuracy you would need to wait some time (min 24hours) to get any decent data.

As you mentioned, Cors or any other system with refrence stations. Process recorded data from base against a nearby station

And since rover is relative to your base, the points you collected in survey mode need to apply the same shift your base would get (the difference between the average used position of the base and the position you get later when you process it against CORS or PPP).
Remember to record the base station coordinates used in the RTK session. Those coordinates is averaged on base and are not saved. You could pick up base coordinates from the base correction log on rover.
I usually do the shift in excel and use UTM coordinates.

There are other ways to get by the relative points on your rover but its more complicated and higher risk of getting error.

Your could read more about PPP shifts here
https://www.nrcan.gc.ca/maps-tools-and-publications/tools/geodetic-reference-systems-tools/tools-applications/10925

When to use CSRS-PPP, before or after the Real Time Kinematic survey?

Suggested methodologies

1. It is preferable to compute the base station’s coordinates before starting the Real Time Kinematic (RTK) work. You could setup the base station ahead of time and collect raw GNSS data (anywhere from 2hrs to 24 hrs depending on the accuracy required). Leave the base station in place. Transform the raw data to RINEX and submit it for Static CSRS-PPP processing. CSRS-PPP can process the data approximately 90 minutes after data collection. Once you have your accurate coordinates from CSRS-PPP, you can begin the RTK work.

2. If it is not possible to collect raw data and run CSRS-PPP ahead of time, the RTK survey can still be performed entering the Base Station’s approximate coordinates. Ensure that base station raw data is recorded (uninterrupted) for as long as possible. Run Static CSRS-PPP after the RTK survey, compute the difference (between approximate and PPP coordinates) and apply a 3D shift to the entire survey. A minor drawback here is that for each ten meters of error in the Base Station position an additional 1ppm (1mm per kilometre) error is introduced in the baseline computation.

3. A popular methodology is to establish accurate coordinates for 2 points within the survey area (a fair distance apart and inter-visible). Collect raw GNSS data simultaneously at both points and post-process both using Static NAD83 (CSRS). Also process both files as a baseline (distance, azimuth) using your phase differential post-processing software. From the CSRS-PPP output coordinates, you can compute the distance and azimuth between points as well (program INDIR, inverse solution ). Comparing these results can serve as quality control plus you now have 2 geodetic control points to choose from. Make one of them the main Base Station location; the survey will be anchored to this point. The other point can be tied with the Rover during the RTK survey (as an additional check) and used as a back sight for traditional surveying.