Setting the base in remote locations

Hi, I’ll be doing some surveying of Ground control points for photogrammetry in a very remote location in Africa. There’s no internet signal or telefone signal available. There are also no known points of interest with known coordinates that I can use.

How should I proceed to setup the base in these areas and get an accurate base location before start surveying with the rover?

(I’m very new to this)

Thanks
Luis

First of all, if you’re not confident in the methodology/process of what you are trying to do, you better either take a crash course on land surveying or take someone with you who is knowledgeable in land surveying, familiar with the use of GNSS equipment and has experience in providing accurate photo target coordinates using RTK or PP capabilities. The work will not just end in the field.

It would not be good to have to revisit the remote site because of your lack of knowledge.

Install permanent mark for the base for future reference, measure instrument height to ARP (antenna reference point), take pictures of base site, bring compass/tape for base site orientation (draw sketch of base site), log base data for a minimum of 8 hours or longer (preferably dual frequency data) and submit data to AUSPOS or Canadian PPP service.

Are the targets in clear unobstructed skies, wiil they be permanent long enough for the flight ? How are you locating the photo targets ? Are the targets within radio range of the base receiver ? How long are the baseline distances from the local base to the photo targets ? If not using radio RTK, sufficient observation time for each target should be a minimum of 30 minutes. If baseline distances are exceeding 5 km, I would recommend a minimum of at least 1 hour per photo target. Make sure you also measure the ARP of your rover for all the photo targets.

Keep good notes ! You may have to revisit the site someday. Good luck !

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Hi again and thanks for the quick reply.

Just to clarify when I said I’m very new to this, I mean I never used Emlid before or RTK to measure the ground control points. However, I did many surveys using drones and ground control points surveys using a total station in Europe (I was not the one using the total station) so to answer your questions, I’m surveying several beaches in several small islands with max 2 kms long each beach. The final objective is to get an orthophoto and DEM photogrammetry model of each beach for inundation simulations and animal’s nest locations in ArcMAp.

In reality I don’t even need a super accurate position on the base as I’m more concerned with the elevation accuracy on my final DEM. Each beach will only be surveyed once so no need to setup a permanent mark for future surveys. I’ll go to 1 beach do the survey of that beach and move to another one to do the same.

So the idea will be to go to a given beach, setup the base on the highwater mark on the sand and have those coordinates more or less accurate in terms of Lon+Lat (<3m error) and set the Elevation of base manually to Zero. Then I’ll survey the ground control points and ideally would have an accurate elevation difference to base <10cm error for each GCP. As for the Lat+Lon coordinates related to base, will the Emlid give me the accurate positions related to the base as well or will this error be bigger?

Many thanks in advance

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Wow, that would be cool to survey on the beach in a remote area. I’ve got 2 M2’S and a RS2 as well as all JAVAD equipment. The Emlids are great receivers for the cost. This should answer your question per the spec sheet.

If you’re using radio RTK, you shouldn’t have any issues with radio range. In my area of SC USA, there’s not much flat lands… mostly rolling hills with hardwoods/pine forests. However, during testing the longest range I’ve achieved is about 3km.

Wish you a lot of luck on your project !

Hi Luis,

Welcome to our community forum! Hope you’ll enjoy it :slight_smile:

Working in RTK, you’ll be able to collect centimeter-accurate points relative to the base. So it should allow getting several centimeters of accuracy for your model.

At the same time, the way you set the base affects the absolute accuracy of your project. We provide a detailed guide in our docs that describes different ways of setting the base. And I see 2 possible options that may suit you:

  • Average Single: you need to place the base and average its position. As a result, your base position will be several meters-accurate

  • PPP service: you need to record a 4-hours log and upload it to the PPP service, for instance, NRCAN CSRS-PPP. If you upload the raw data log from Reach RS2 after 90 minutes of recording, you’ll get the base position with 15 cm of accuracy. To learn more about working with PPP services, I’d recommend you to check this guide

It’s essential to set the correct elevation for your base. Otherwise, the rover won’t be able to calculate a Fix. However, you can correct the heights of all the points manually after you finish the survey, so the base height becomes 0.

Also, just want to agree with Bryan’s suggestion of using the LoRa radio to pass the corrections from base to the rover. The normal operating range for Lora radio is 8 km in line of sight. So as your working area is quite small, I believe it’ll work well for you.

Hi Julia, thanks for your reply.

A few questions:

1- you mentioned the PPP service, but since I’ll have no internet or phone connection I wont be able to upload anything anywhere so therefore this option would not work right? Or do you mean doing this in post processing once I return home to Europe and correct all the survey?

2- “It’s essential to set the correct elevation for your base. Otherwise, the rover won’t be able to calculate a Fix” - Can you elaborate on this please? for my objectives I want that all the water and anything bellow high tide mark to be considered zero elevation, so I can then calculate flooding scenarios on the beach. So if I manually set the base elevtion to Zero and start a survey, will I get accurace differences between the base elevtion and rover elevation? Say I set the base elevation to zero and then measure a GCP which is 1m above the base in terms of elevation, will my survey show the elevation of that GCP as 1m?

Thanks for your help

Luis,

Oh, you are right. The Internet is needed to upload files to the PPP service. But you suggested a good idea of post-processing the data. You can use our Stop & Go feature for it.

To use it, you need to Average single the base and collect points with the rover parallel recording raw data logs on both receivers. After post-processing them in Emlid Studio, you’ll be able to achieve centimeter-accurate points. All steps of the workflow are also described here.

You can preprocess the data in your work area to ensure that you get centimeter-accurate points relative to the base. Once you come home and get the precise base position from the PPP service, you’ll be able to process the data once more and get absolute accuracy.

I think that I understand the idea of your project. However, RTK and PPK algorithms can’t calculate centimeter-accurate points if you set the base height as 0. That’s why a workaround is needed.

To get all heights relative to the base, you can manually subtract base height from points’ heights after the survey. As a result, you’ll get correct horizontal coordinates and heights, which would be if the height of the base station were 0.

Hi Julia,

Thanks again for the extra info.
So, I went to do a test on the field and do a survey. I got fixed lock, took 4 points in the survey which I can see in my survey menu from the rover and can export as well. So far so good.

Wanted to try the post processing but the tutorial here: https://docs.emlid.com/emlid-studio/ppk-workflow/ is not made for newbies so I was wondering if you could help.

1- the tutorial says: “To perform post-processing, you will need the following files:
a RINEX observation file from the base
a RINEX observation file from the rover
a RINEX navigation file from the base or from the rover”

How do I make sure I’m recording these observations when I start surveying? is it automatic? Do I have to do anything?

2- then the workflow says “Choose one of the positioning modes:
Kinematic mode: for the moving rover…”
Where and when? When I do the survey? I did the survey on Kinematic mode but this seems like something else.

3- Then it shows an image of a PPK screen that I cannot find on the reach panel. Where is this screen?

4- Then says “Add the RINEX observation file from the rover.” - where do I get these files from? I can see on the logging menu the “logs” in the end. Is it here? But these seem to have ALL the logs and not setarated by survey, so I dont understand.

Can you help?
thanks

Hi Luis,

I’m here and ready to help you walk through it. Feel free to ask me if something is unclear :slight_smile:

To post-process the data, we provide an Emlid Studio app. It’s free and available for both Windows and macOS devices. So the PPK guide you’re trying to walk through refers exactly to it.

To record and download RINEX raw data logs, you need to go to the Logging tab. There you can also set the logs format, version and if it’s needed, set automatically to start recording them once the receiver turns on.

Observation and navigation files are the parts of the RINEX format. So if the RINEX log is recording, you can be sure that you’ll get both of these files.

These files are indeed in the same Logging tab at the bottom of the page. Each log has a time when the recording started, the main info about the file, and its weight. After the logging is stopped, you can download the files there.

Just one more note: I see that you are using the Reach Panel app. However, we recommend using the mobile ReachView 3 app instead. It contains all the last fixes and improvements. The app is also free and can be downloaded from Google Play or App Store.

Hi Julia,

Ok, so In the logging, I’ve changed the Raw data to Rinex 3.03 and set it to automaticaly record.

I’m guessing the Raw data is the only file we need to export to the Emlid Studio right?

When I’m done processing in Emlid studio I get 2 Files .Pos . where do I open these files, since what I need is a LON, LAT, ELEV data for each point on the survey like I get with the CVS file when I export the survey file from the rover.

Thanks again for your help.
Miguel

Hi Again,

One more question, should I use the general coordinates WGS84 or the local coordinates. I’ll be surveying in Guinea Bissau which has UTM 28N. Can you advise?
Thanks

Hi Miguel,

POS file from the Emlid Studio contains the position data for the whole survey. To get coordinates for the exact points in PPK, you need to use Stop & Go feature. This guide explains all the steps of its use.

To work with Stop & Go in Emlid Studio, you need to upload:

  • raw data logs from the base
  • raw data logs from the rover
  • CSV file with collected points from ReachView 3 app

After post-processing, you’ll get a CSV file with corrected coordinates of the collected points.

The coordinate system of your project doesn’t affect working with the Stop&Go feature. So you can set it by default.

All points output from Emlid Studio in WGS84 with ellipsoidal heights. However, if your project requires them to be in UTM 28N, you can apply a projection to the points using QGIS app or online services such as ToolOnline.

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