Reach RS2 PPK Workflow for logging and surveying

Reach RS2 / RS2+ RTK / PPK configuration
1

Hello-
I’m new to the Emlid family having recently purchased 2 RS2 receivers. Some quick background info, we fly sites with a non-RTK drone equipped with an Applanix GPS/IMU board for agricultural mapping in rural areas where CORS networks are >80km away. Many of our sites are 4+ hours away and we are trying to fly multiple fields in 1 or 2 days, spending at most 2 hours at a site.

Question 1: So for starters, I would like to use one RS2 as a base for logging raw data to be used to post-correct our drone trajectory. Applanix has said the log files should be in RINEX format, using all GNSS types, using the static position mode in RTK settings, and 1Hz update rate.

To match these specifications for Applanix, I would go to RTK settings and select “Static” as my position mode, select all GNSS types, select 1HZ rate and then begin logging the Rinex file. Correct?

Question 2: Some sites we will want to use and survey the absolute position of GCPs. Again, these sites are hours away from our home site so using PPP is not an option so I assume PPK is the best option. What would the workflow look like if we are trying to survey GCPs and logging our raw data during our drone flight for post-correcting Applanix trajectory? It seems like the position mode in RTK settings would be different for the base depending on whether is being used to survey (kinematic mode) vs logging data (static) for Applanix? Could someone please suggest a workflow along with the appropriate Emlid settings?

Thanks

3

Hi, i`ll take a shot at this from my point of view

This is more or less a YES. The important one is GNSS and HZ. Select all GNSS is almost a nobrainer unless you have a storage issue or really know that you are not going to use a specific satellite system.
Hz is like resolution on a camera. Its easy to crop down but hard/impossible to gain more pixels.
Usually 1hz is enough for base stations taskes. If you are not sure and have enough space and time for 5/10 or even more, then go ahead, use a higher frequency.
You will have more work later one processing it down to a lower speed if only 1hz is needed but at least you are not totally lost.

This is a bit more tricky.
The first question i would ask. What absolute accuracy do they need?
Relative accuracy is not that hard (relatively speaking phun intended) and should give you the accuracy needed by just having your base up and running( recording data too) along with your rover within the baseline limits.
At least for the base-rover part.
Camera, lever arm etc or other kind of gear used i can not say as i dont have the spec for it.

Assuming its all PPK /static (base accuracy), i would reckon you should get a horizontal accuracy within 2-4cm with a CORS network >(greater then) 80km away from your base and also having a NrCan tool in backup.
I also assume you have around 2 hours of base data to process. 2 hours is just about enough to get you into the the ball park of 2cm horizontal accuracy in my area with your numbers and the right PPK tools for PPP. For Z values you need to double that.

Edit: Sorry, i missed the gcp part in the last question.
If a RTK link to your base is possible, then doing the GCP survey in RTK mode with base is the way i would do it. Then you will have all your accurate relative measures between rover and base and
when your final PPK/PPP job is done with the base, you only have to apply a shift to the coordinates you created.
There should be more details in this forum on how to apply a shift, if you do a search.

Hope this was helpfull

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4

Thank you TB_RTK!

I have some follow-up questions.

  1. Does the positioning mode in the RTK settings (static vs kinematic) matter when logging raw data on the base and rover? I plan to use the PPK workflow found in Emlid’s documents to post-correct my base and rover logs. I saw a recent post on the forum that said the only data selection important for logging is the GNSS selection? Is this correct?

  2. The reason for the question about positioning mode during logging is because when I use RTK to survey my GCPs, I am setting my base and rover positioning mode to kinematic.

  3. When surveying my GCPs, how long is a reasonable time to collect data at each point? Again these points with be run through the PPK workflow.

  4. In the logging tab of the app, what is the position and base correction log used for? Do I need this for PPK?

5

No. Only if you have some kind of correction input active.

Enable raw logging, GNSS selection and HZ are the ones you use with PPK

If using base-rover configuration, you need the base coordinates with RTK survey. You set the RTK mode on the rover.

Depending on your need for accuracy. I reckon somewhere between 5-30 epochs and do a check later on if you got the time or need for it.
I prefer two short measures with some time between rather then one long one.

For the base you need the raw log only. For the rover and GCP points i only use the RAW and base RTCM for backup, and use the surveyed points exported from the survey menu to get the coordinates from the RTK session.

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6

Sorry for all the questions. Trying to wrap my head around the process.

My thought was to use the RTK base - rover configuration and the survey tab in the app for surveying my GCPs. Since I don’t know my base coordinates, I was going to use averaging single for 20 or 30 minutes. During this whole process I would also be logging the base raw data for PPK.

My thoughts on workflow in the field for collecting and post-correcting GCPs:

  1. Setup base RS2 over an unknown point
  2. Setup base for RTK surveying (kinematic position, LoRA settings, GNSS selection, HZ rate)
  3. Begin logging base RAW data - used for PPK of base done on a later day
  4. Begin average single of base for RTK - averaging time of 20-30 minutes
  5. Setup RS2 rover (kinematic, LoRA setttings, etc)
  6. Beginning logging RAW data - used for PPK of rover?
  7. Use survey app while in RTK mode to collect coordinates of GCPs (5-30 epochs per point)
  8. Stop logging of base and rover
  9. Export base raw file, rover raw file, and survey GCP coordinates

Does this sound like what I would need for post-correcting my GCP locations? Should I also be logging the corrections of my rover, is that what you are suggesting?

For PPK workflow, I am first correcting my base with a CORS station. CORS is about 80km away. Correct?

How do I correct my rover on site? Am I using the logs or can I do something with my exported survey coordinates?

7

If you intent to post-process the Base Location anyhow, then no need to average for so long. 2 minutes should be plenty to not be completely off on-site.

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8

Yes.
I would probably use much shorter average. 2-3min tops. Instead boot the base up as soon as i get into the field and after other gear is out and after few minutes of warmup, when the base has passed the cold start, i would start the average. I dont see any point using long average time as long as the base shows you are in the ball park and do not jump all over the place (max 10-15m)

Other then that it seems you have the basics all sorted out. Well done.

You could, but since you log raw data back at base you really dont have to. As long as you remember to turn on logging.

Yes. But also remember to note the base coordinates when you do the RTK in the field. Take a picture or a screenshot of the base coordinated used.

When you have done the PP of the base, you need to apply the same shift you get from average base and PPK base coordinates to all your captured points from survey. This is done in e.g a spreadsheet.

Here i did the shift for another user. As an example

9

There are other ways to adjust coordinates on the fly.

E.g with Survey Master that i sometimes use.
All points is surveyd in RTK with an averaged base. After PP of the base, your shift is computed (e.g X=-1,234 Y=2,345 X=3,456)
In Survey Master, the site calibration (localization) is used to adjust for base location. When i export these coordinated now, they are all adjusted with the shift that i applied.

Easy peasy

You could probably survey all your points with Reachview, export to Survey Master, apply shift (localize) and then export.

10

Thank you! This is all making sense now. I think the part that I wasn’t getting is that there are multiple ways to correct my GCPs. One is applying the shift after doing a PP of my base and the other is using the log files from my rover. I guess with the log files method, I don’t need to use the survey function in the app, just sit over each GCP. Applying a shift seems much quicker and easier.

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11

I thought of another question, this time relating to using OPUS to correct my base.

I have a site we fly locally, so I set up my base and collected RAW files for 3 hours. I uploaded to OPUS and now have the report.

I need help understanding what coordinates to us? I’ve read a lot of articles on accessing the quality but I am having trouble understanding what values to input into the manual base mode of my RS2.

On my report:
There are coordinates under: Ref Frame NAD83(2011), ITRF2014, a section with (Lat, E LON, W Lon, EL hgt, ortho hgt), and then UTM coordinates.

What should I use for my base coordinates? And do I need to convert them?

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4 posts were split to a new topic: Difficulties with getting fix in PPK

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Someone with local knowledge should answer this question. There`s probably a transition that need to be done.

17

Hi Matt,

Welcome to our community!

I want to sum up the following points:

To match these specifications for Applanix, I would go to RTK settings and select “Static” as my position mode, select all GNSS types, select 1HZ rate and then begin logging the Rinex file. Correct?

Yes, you can choose the settings in the RTK Settings tab. Reach RS2 should log data with the settings just fine. However, we haven’t tested Reach RS2 with Applanix.

Some sites we will want to use and survey the absolute position of GCPs. Again, these sites are hours away from our home site so using PPP is not an option so I assume PPK is the best option.

We don’t have a ready-to-go workflow for GCPs collecting in PPK. The data is collected as 1 continuous log, so you will need to extract the data for each point manually. To do it, you need to save the start and end time for points during the survey.

What would the workflow look like if we are trying to survey GCPs and logging our raw data during our drone flight for post-correcting Applanix trajectory? It seems like the position mode in RTK settings would be different for the base depending on whether is being used to survey (kinematic mode) vs logging data (static) for Applanix?

The workflow for Reach receivers is the following:

GCPs collection:

UAV PPK:

  • Set up the base. To get absolute accuracy, you should place it on a known point.

  • Enable logging on the base

  • Enable logging data on the rover installed on a drone

  • After the survey, process the data from the drone with the base data

You can set the Static mode for the base in both cases, as the unit doesn’t move. The mode can help to resolve ambiguities faster.

For PPK workflow, I am first correcting my base with a CORS station. CORS is about 80km away. Correct?

The atmospheric conditions might affect the satellite signals’ transmission. If there’s a long distance between the base and rover, the difference between the atmospheric conditions becomes significant. We’ve tested that Reach RS2 can get centimeter-accurate coordinates in RTK on up to 60 km baseline. On the 80 km baseline, the result may have a bit worse precision.

There are coordinates under: Ref Frame NAD83(2011), ITRF2014, a section with (Lat, E LON, W Lon, EL hgt, ortho hgt), and then UTM coordinates.
What should I use for my base coordinates? And do I need to convert them?

At the moment, you can enter the base coordinates in ReachView 2 only. The app requires a position in WGS84.

However, the NAD83 ellipsoid is quite similar to the WGS84 one. So, you can enter the coordinates in NAD83 without issues as well. In this case, the rover coordinates will be calculated in NAD83.

Please note that you can’t enter the base coordinates measured in metric units (like in UTM), as in this case, the calculations are made another way.

18

Hi - excuse me for jumping the thread…

I would like correct my UAV-rover data using an RS2. I survey in locations without CORS/NTRIP or similar. So my plan was to log the RS2 for 4-5 hrs as recommended elsewhere in this community and then PPK my rover to my base. But the absolute accuracy of my rover will be the RS2 accuracy which essentially is “Single” or 1-2[m]. So I thought to PPP with NRCAN as discussed elsewhere in the forum to get down to [cm] level on my base. But that leaves me with a single coordinate for the base (.pos file for the base) that can not be used say with RTKLIB for PPK since the requirements for PPK are OBS files of the rover and base over the same time period of observation.

My question is - what is the flow for my purpose?

Is it :

  1. Log base for 4-5hrs and collect RINEX
  2. Fly rover and collect the RINEX
  3. PPK rover to base to get relative [cm] accuracy but still maintain 1-2[m] absolute accuracy.
  4. PPP my base RINEX with NRCAN to bring thebase to [cm] level accuracy.
  5. Find the shift between the original base coord’ and NRCAN’ed coord’
  6. Apply the shift to all the coordinates of the rover found in (3) above via excel/QGIS/etc as discussed elsewhere in the forum.

Is it possible to PPP my base and get back an OBS file in order to then PPK the rover directly and get [cm] level positioning of the rover right away?

I’m trying to streamline the process in order to go through many surveys rather than just doing it on few occasions. Is there a faster way to do the above and say remain all within RTKLIB (through command line interface) that would allow to forgo the excel or QGIS?

Thank you very much !

19

Incidentally, when I try to use NRCAN for PPP, I don’t see how to select ultra rapid, rapid and final solutions. I seem to simply get a response which is either rapid or final without having any control over it.

How does one select the desired solution on NRCAN?

Tnx

20

The PPP service simply gives you the best solution possible available at the time of submission. Ultra-rapid is within a few hours of observation (I think the system was upgraded and now it’s even shorter, under 2 hours), rapid is about a day after, and final is about two weeks later.

About your workflow, it would be simpler to send your base data first to the PPP, then use the returned precise base position as the true position in RTKLib when you want to post-process the rover data against the base.

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21

Don’t put too much into what solution you get from NRCAN when using multifrq, pay more attention to your obs-times: Study of deviation of PPP with RS2 with different observation-times - #5 by wizprod

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22

If I wanted to apply a shift to my rover points using just a spreadsheet like excel, do I just find the difference between my base lat/lon of the corrected and average positioned base? My coordinates are in decimal degrees latitude and longitude.

Corrected base lat: 40.7201186694 degrees
Average base lat: 40.7201284977 degrees

When I look at the points in a GIS software, they are about 1.6m apart.

23

You could probably use lt/long if you find the right tool but I usually use UTM as its much easier without a complex formula.

Yes.

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24

ok - but when processing in rtklib I will still use the original obs file from the base. You say that if I use this original obs but place the corrected precise base location after PPP here

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my position file for my rover after PPK will be at the absolute accuracy I got from the PPP ?