Hi Guys, I have to admit I am not familiar with a lot of the packages, terms, and tools you are talking about in this forum. I do have Linux experience, but not so much hardware interface experience.
Could someone provide some hints on the most basic steps to retrieving either live or recorded IMU data from the Reach? I’m looking for stuff like: (1) What cable needs to be plugged into my Ubuntu 22.04 desktop Intel NUC? (2) Is there an approach that can transfer the recorded data over WiFi? (3) How to get the Reach to record the IMU data, or does it already do this? Is this what RTIMULib does once it’s installed on the Reach? If so, what scripts or install should I look at to make it happen?
For my workflow, literally all I need is the recorded accelerometer and gyro measurements, no calibration or anything else will be necessary, although I suppose that would be nice.
It’s not possible to record such information about IMU with Reach. One possible option is to stream the NMEA ETC message from Reach RS3. It can provide you with real-time information about the actual operation of tilt compensation.
Thank you for the answer Kornel. That is disappointing. Very interesting to have an IMU but not allow that data to be output, I think the Emlid products are the only GNSS/INS packages I’ve seen with that limitation. It certainly limits the use-cases for the sensor. Is there a technical limitation of the hardware preventing output of IMU data, or just software at this point?
Hi Kyle,
If you are after using raw IMU readings with a 3rd party software (or your own software), it is not supported by the M2/RS2/RS3 receiver.
The NMEA ETC message contains the tilt angle of the receiver (that is, the inclination of the pole) as well as its north-heading at 1-5 hz, but not the 100 hz raw readings of the IMU. My understanding it the receiver uses these raw readings and some fancy math to calibrate the IMU and then calculate tilt compensation.
The NMEA stream even provides the location of the receiver before and after tilt correction is applied.
I believe IMU readings could be accessed some a few years ago (have a look at the forums, it involved ssh-ing into the unit and doing some fancy configurations) but at some point that option was closed.
In summary, if you want IMU readings, either Emlid updates the firmware or you will have to use an external IMU. There are multiple options, even some of then can communicate using bluetooth and wifi.
Hi Kornel, the main application for my project is LiDAR mapping from a drone. If I have access to raw GNSS and IMU data, I can combine them in post-processing (PPK) to get centimeter level accuracy in position as well as <50 arcminute level accuracy in orientation. Without this, we have to go to much more advanced, complex LiDAR mapping approaches that don’t necessarily guarantee an accurate geo-referenced map.
Errors according to the RS3 specs are:
RTK: H: 7 mm + 1 ppm | V: 14 mm + 1 ppm
Tilt compensation: RTK + 2 mm + 0.3 mm/°
You can expect 1-2 cm of error (with RTk, a pole of 1.8m and a small tilt angle). We have used it extensively and it is pretty good.
For your use case with lidar on a drone, I could not tell. One of the big questions is how to synchronize the timestamps of the lidar and GPS and make it work with the different frequencies of the devices. Such setups tend to rely on very accurate IMUs…
Thanks Fernando, this is what I was suspecting might be the case. We have a backpack LiDAR setup with a tactical grade IMU and big UFO-like GNSS antenna, using PTP to time sync everything together. We get great results from that. I wanted to see what was possible with something like an Emlid Reach, but maybe I don’t need to go that far down that road and can just tell my superiors that it won’t be accurate enough for what we need.
