ELT RTK Base

Determining Coordinates

Determining coordinates is necessary to find the exact coordinates of the antenna. Start with a rough determination of coordinates using the built-in PPP, then refine the coordinates using one of the more accurate methods. Before determining coordinates, be sure to read the section on accuracy and stability on our blog.

Frames and Epochs

It is very important to remember about frames and epochs. Ublox has a good tutorial on this topic, and a brief explanation can also be found on Onocoy. The PPP and HAS methods give results in the ITRF frame associated with the Earth's center, while the RTK methods sometimes use the ETRF frame associated with continents. The difference between frames in Europe is currently about 80 centimeters, so it is recommended to use a frame calculator for conversion.

Determination Time

The determination time should be no less than a full day, ideally 23 hours and 56 minutes (86160 seconds). For high accuracy, it is better to use several daily RTK measurements and perform adjustment. The most accurate way is to hire a surveyor or use a paid service.

Antenna Stability

The main condition is that the antenna should not move relative to the ground. High bending masts are not suitable.

Specifying Coordinates

When specifying coordinates, there are two main options:

• If coordinates 0.00 0.00 0.00 are specified, the receiver determines its coordinates by averaging the autonomous solution within a minute.
• If other values are specified, the receiver tries to establish them.

If the coordinates are incorrectly specified (more than 50 meters from the value determined by the receiver), the Unicore receiver will not work. In this situation, only the Beidou and QZSS satellites will be visible on the Status page. To avoid this, when specifying incorrect coordinates in the settings, the receiver uses the averaged value of the autonomous solution. The indicator next to “Main service” will be orange, not green.

Status Indicator Colors

• Green — everything is fine.
• Yellow — the service is running with errors.
• Red — the service is not running.
• Blue — the service is currently in the process of starting up.

Determining Coordinates using the PPP Method

To determine coordinates using the built-in PPP, go to the Status page after a day and copy the coordinates as described “Checking Satellite Reception”. Note that each time the base coordinates or other main service settings are changed, the PPP refinement process starts from scratch.

Download and Unpack

Insert the SD card sent to you into your computer's card reader and download the self-extracting archive WinRtkBaseUtils.exe to your hard drive. You can also download this archive from GitHub using the provided link.

Run the file to unpack it. During the run, you can choose the folder for unpacking and click the Extract button.

Sometimes the antivirus may give a warning, and you need to explain to it that this file is safe. For example, Microsoft Defender may display the following message. In this case, click “More Info”.

Next, click “Run anyway”.

Important Requirements

Important Requirements

To determine coordinates using the WinRtkBaseUtils package, you must enable the “Rtcm tcp service” by clicking the “On/Off” button to the right of “Rtcm tcp service”, and after determining the coordinates, disable it again. Enabling this service allows access to change the receiver settings from outside the Raspberry PI, and in the worst case, even outside your local network. The list of messages for this service is obsolete and does not affect anything.

Moreover, if there were failures during the execution of RTK.bat or HAS.bat, you must reconfigure the receiver as described in the “Configuration” section. The WinRtkBaseUtils package reconfigures the receiver, and in case of a failure, it must be reconfigured back.

It is not possible to run multiple RTK.bat or multiple HAS.bat from the same directory simultaneously, even with different Raspberry pi and receivers. This is due to the impossibility of simultaneous use of the same temporary file. Trying to do this will result in a message like the one shown in the picture.

If the receiver firmware version is outdated, there may be messages like the one in the picture. In this case, check the receiver firmware version as indicated in the “Checking the Receiver Firmware Version” section.

After changing coordinates by clicking the Save button, all services are stopped. If the “Main service” was running at the time of clicking Save, it will restart, but the other services will remain stopped.

Determining Coordinates via RTK

RTK stability on Unicore receivers is about 4 mm CEP50 horizontally and 8 mm CEP50 vertically. Accuracy is approximately 1mm per kilometer of distance between the receiver and the base. For increased accuracy, network corrections with virtual bases should be used.

Before using this method, you need to locate a nearby base station and obtain its NTRIP v1 parameters. This could be a free base station from the IGS. EUREF, RTK2go networks, or a paid station from Onocoy, Geodnet, or other providers. I can't say which network is most popular in your country—that depends on local conditions.

It’s important to determine which reference frame your base station uses and which frame you intend to use for your own coordinates. The RTK method provides coordinates in the same reference frame as the base. If needed, you can convert the resulting coordinates using a reference frame transformation calculator. Onocoy provides a clear explanation of what reference frames are and why there are two of them (ITRF for GNSS and ETRF for mapping).

To determine coordinates using RTK, run the RTK.bat file. In the opened window, enter the receiver address and port. If you use Raspberry pi on the local network, do not change them. Then enter the address, port, mount point, login, and password for the NTRIP server, as well as the measurement time. The entered parameters are saved in the Ini.cmd file.

Communication with the receiver and server is checked, then the receiver is configured, and then RTK starts.

In the end, the coordinates are copied to the clipboard and displayed on the screen, and the receiver is configured back to base mode. For early termination, press the Q button. After completion, press any key to close the window.

Determining Coordinates via HAS (Only Unicore)

Determining coordinates using the HAS method is available only for Unicore receivers. To do this, run the HAS.bat file. In the opened window, enter the receiver address and port. If you use Raspberry pi on the local network, do not change them. Then enter the measurement time. The entered parameters are saved in the Ini.cmd file.

Communication with the receiver is checked, then the receiver is configured.

HAS resolution starts in 2–10 minutes.

In the end, the coordinates are copied to the clipboard and displayed on the screen, and the receiver is configured back to base mode. For early termination, press the Q button. After completion, press any key to close the window.

Determining Coordinates via External Services

Using External RINEX Services

Another method is to use an external RINEX post-processing service operating in your region. For example, for France, IGN services (instruction) and Orpheon are suitable, and for the rest of the world, NRCAN. Such services are usually paid.

Recording the Measurements

First, enable the “File Service” and record the measurements. You need at least one full day according to Greenwich. The fact that recording is in progress is visible on the Logs page by the increasing size of the rtcm3 file. For this, only one file should be recorded per day. Turning off the device or stopping the file or main service will result in the daily archive being unsuitable for conversion to RINEX.

Converting to RINEX

After recording, go to the Logs page. Click on the pencil icon next to the full-day ZIP archive file. Unfortunately, only ZIP-format files can be converted to RINEX. Ideally (and for Centipede), use an archive older than 15 days so that the service can form final satellite orbits.

A window like this will open. For NRCAN, select “Nrcan”, for IGN - “Ign”, and click the “Create RINEX file” button.

A message indicating the file creation process appears. Wait a few minutes.

The RINEX file is created. Click “Download it!” to download it.

During the download, a message about unsafe downloading may appear. Click “keep”. The downloaded file size is 6-8 megabytes.

After downloading, the created file can be seen in the log list for re-downloading.

Registering with NRCAN

Next, you need to register (or log in) on Nrcan.

Click “New User: Create an account!” and fill in the details. After completing the form, click “Submit”.

You will receive a message that an email has been sent to you.

Open the email and activate your account by clicking on the link.

You will receive a message confirming successful registration and a prompt to log in.

Click “Sign in” and log in.

You will be greeted with a message congratulating you on successfully logging in. Click on “Geodetic

tools and data”.

You will land on the “Geodetic tools and data” page. Click on “Canadian Spatial Reference

System Precise Point Positioning (CSRS-PPP)”

You will be taken to the PPP calculation page. Select ITRF (not NAD83) and Static (not Kinematic).

Scroll down the page. Click “Choose File” to select the RINEX file, and then click “Submit to PPP”.

After processing, you will receive a message that the result has been sent to your email.

Open the email and click on the “summary” link.

Follow the link to view the coordinates in the ITRF2020 frame.

Another interesting section in the report is “Orbits and Clocks Used”. In our example, it shows

“Ultra-rapid”, but if we had waited 15 days, we would have received the much more accurate “Final”.