RTK GPS (Emlid) Field How-to

Equipment needed:

Communicating with Emlids. Need the Emlid Flow app on phone or tablet. I've been using bluetooth (which is technically beta). Only place it won't work is downloading the base datafile (then wifi seems necessary). CU's internet authentication setup will not allow the Emlids on campus network.

Preparing base station: (can be before going to field; presuming naming, etc., complete; most if this probably carries over)

  1. Connect to the base unit.
  2. Go to Settings [not Base Settings] and tap GNSS settings. Pick each of the satellite systems.
  3. Set the GNSS update rate at 1 Hz. [UNAVCO had suggsted 5 Hz, but seems only suggested for rover]
  4. Return to the Receivers screen. On the Base settings screen, go to RTCM3 messages.
  5. Select to output RTCM3 messages as follows:
  6. Tap Apply.
  7. Return to the Receivers screen. On the Base output screen, select LoRa.
  8. Tap the Edit button in the LoRa cell. Select frequency and set the output power at 20 dBm.
  9. Set air data rate at 9.11 kb/s. Tap Save.
  10. Return to the Receivers screen. Select Logging, then Recorded logs and settings. (This usually requires a connection through wifi, which often automatically happens).
  11. Tap the gear icon at upper right. Click on OPUS as the format. Enter RINEX 3.03 for the format (unless you know better). Click Apply button at bottom of screen.

Set up rover:

  1. Connect to the rover unit (on the Receivers page).
  2. Go to Settings and tap GNSS settings.
  3. Select the same GNSS systems as for the base, and set 5 Hz GNSS update rate. Apply changes.
  4. To configure LoRa radio on the rover unit to receive the corrections, return to the Receivers screen and tap Correction input.
  5. Select LoRa. Set the same frequency and air data rate as for the base. Tap Save.

Create a project:

  1. Open Emlid Flow and go to the Survey tab.
  2. Either choose an existing survey or tap the Plus button in the top right corner to open the New project screen and fill in your project info.
  3. Specify the coordinate system you want to work in. NOTE: Most non-WGS coordinate systems will require a download.
  4. Select the measurement units for your project from the Linear Units drop-down menu.
  5. Select the angle display format: DD or DMS.

Can turn off Emlids until needed in the field.

 

Field setup:

  1. Mount Reach RS2/RS2+ base (the 50 cm extension is needed on regular tripod).
  2. Accurately level the tripod.
  3. Put the rover (RS3) on the pole.
  4. Attach LoRa antennas to both units.
  5. Turn on the receivers. [This MUST be after the base is installed or your log file will be a problem]

After placing the base on the tripod, you can complete its setup:

  1. Connect to the base.
  2. On the Receivers screen, tap Base settings.
  3. Measure the antenna height from the bottom of the EMLID to the ground.  (The internal height in 2+ is 134mm, which is automatically added, so just measure to the bottom of the device). Enter in Base Settings page.
  4. Tap Coordinates Entry method. Select Average SINGLE as the base coordinates entry method and set averaging time (default is 1 minute; I've used 5; regardless, until this completes, you won't get differential locations). Tap Save. [If a known point, choose Manual and
  5. After accumulating the data, you will see averaged coordinates in the Base marker section. Now your base is set up and transmiting corrections to the rover. Write down the location from BAse marker as that will help troubleshoot any later problems in elevation.

Now connect to rover (RS3):

When you completed your RTK setup over LoRa radio, you can see the current solution status in the top right corner of the Emlid Flow app:

After a short period of time, the rover gets a fixed solution. In good environments, it will take a few seconds to get a fixed solution. In tough conditions, it may take a little longer. Once rover gets FIX, you are all set for surveying.

You can also find the current solution status as well as your position in real time on the Status screen.

Tilt correction for rover (optional):

  1. Open the Emlid Flow app.
  2. Connect to your Reach RS3
  3. Set up RTK connection and wait for FIX.
  4. Once you've got FIX, watch the tilt compensation status in the Status bar (top of screen). Once initialization is complete, you will need to rotate the receiver or simply walk with it for a few seconds until you hear the notification sound and see the message indicating that the tilt compensation is ready.
  5. You can turn this off in the Survey Settings page. Turning off the IMU sensors will save battery power.

Survey points:

  1. Go to the Survey tab and open or create a project.
  2. The height of the pole (2m for us) should be visible; enter if needed (often shows up in Base Settings for the rover, which is a little confusing)
  3. Tap the Plus button to open the Collector menu. There is a gear to left to set averaging time (defaults to 0, which is just a single measurement.  5s seems OK, 30s might be somewhat more precise).  Can also set a maximum uncertainty to accept a FIX location.
  4. Collect the point. You have options to name it, etc.

You can see the location of a point by tapping on it in the survey map and swiping up from the bottom. Both the local and global coordinates will be available (so if you use a state plane, which gives UTM-style numbers and elevations above sea level, you can also see WGS lat lon and height above geoid).

When survey is over:

Connect to Base, go to Logging and stop logging there to avoid messing up that file. If you haven't already, make a note of the position the base has been using (if not a predetermined point). Probably wise to download the log (Logs section at bottom of logging screen) then before shutting down the base (tap on base receiver name and then Shut Down twice). Similarly will want to download from the rover before shutting it down (in the Survey tab, should see project name at bottom; swipe up to reveal Download options. Note that the data is already on the device; this is to get it into other software. Continuous log probably requires accessing the rover itself like the base as described below).

Downloading:

This is from the phone or tablet controlling the survey. For the points surveyed, open Emlid Flow. Click on Survey button and choose the survey you want to download.

For the Base log file (needed for OPUS check on location used), have to have the Base station on. Connect to the Base. Select Logging, then Recorded logs and settings. Choose the desired file (listed by date) and tap the down arrow at right. You then have choices. (this did work in bluetooth recently). Or you might get hit with a demand to connect to the receiver's wi-fi hotspot...which then won't connect but a retry it does connect (it seems) only to not allow you to download any files. Solution there was to get a laptop on the hotspot wifi, find the IP address in the Wifi settings page, use a web browser to go to the reciver's IP location (http://192.168.42.1 worked for my trouble). [You can also put the receiver on a local wi-fi, though the CU wifis are kind of unhappy about allowing much from a device like an Emlid]. If you connect OK will see the Emlid screen; go to Logging at the left and choose to download file(s) desired.

Processing:

This blindsided me, so worth some mention; the key element is that the rover only figures its position relative to the base's antenna (specifically the antenna phase center); it knows nothing about the height of that antenna at the base.

If setting up the base with a known location there is no issue so long as you properly enter the height of the antenna above your reference point. The base will adjust and transmit the location of the antenna, and the rover locations will be correct.

If using a base that has to acquire a location (so a "SINGLE" location), the base will transmit the antenna's presumed position obtained by averaging at the start. When you go to post-process the location to get an accurate position, if you enter the height of the antenna's reference point, OPUS will give you the elevation of the spot on the ground. To correct the rover points, you need the difference in the computed height of the base antenna added to the elevation of the rover points.

A wrinkle is that the OPUS solution is apparently to the antenna reference point (ARP), which, on the Emlid 2+ is 13.4 cm below the antenna phase center (APC). It is the APC information that is sent to the rover. In entering the info for OPUS, you should aparently use the ARP. If you enter the APC by accident (as might happen if using values from the rover csv file), the ground location will be 0.134m too low, so need to add back in 0.134m.

So, for instance, a base point is placed on the ground. The antenna APC is 1.5m above that point. The base gets its own estimate of its position, yielding an elevation of 1500m on the ground and 1501.5 is transmitted to the rover (which would then show up in the exported rover location file). The 1500m elevation is not saved anywhere unless written down [it might be buried in one of the log files but I haven't found it]! The rover gets a point at 1510m. After the survey, the base log file is uploaded to OPUS with the correct antenna ARC height of 1.366m; this returns an elevation of 1501m for the point on the ground. To correct the rover, the difference between the two elevations on the ground must be added to the rover elevation, or the difference between the two estimates of the antenna position. In this case, the 1.0m increase in elevation estimate of the base is added to the elevation of the rover point, which is now 1511m. What you do not do is use the difference between the base elevation from OPUS and the base elevation recorded by the rover, as these are different points.

 

Please send mail if you encounter any problems or have suggestions.

ERTH4714/5714 public home | C. H. Jones | CIRES | Dept. of Geological Sciences | Univ. of Colorado at Boulder

Last modified at Saturday, October 3, 2026 9:27 PM

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