My team and I are currently preparing a demonstration that requires accurate, real-time tracking of an electrical prototype car to create a VR-overlay.
For this application, we are looking for a GNSS solution that meets the following requirements:
Minimum update rate of 20 Hz
RTK-level accuracy (at least 1.5 cm CEP)
Reliable performance under dynamic conditions
Temporary setup (demo at several locations), meaning easy configuration and portability
There is no internet available, but the demo radius will stay within 1km and with open sky.
Looking at the SparkFun product portfolio, we found the RTK Express as potential base, combined with the RTK Express Plus as rover. The RTK mosaic-X5 (as rover and base) would also be an opportunity, but we did not find clear information regarding its suitability for dynamic testing scenarios and ease of configuring. Any other solutions are always welcome!
What would you advise as the most appropriate solution for our use case?
My suggestion to also consider the Facet FP was driven by your comment below:
The FPL is +$150 over the RTK Mosaic-X5, and seems like a better fit.
If the IMU is critical for your project, then maybe not?
I don’t know how much longer the Express and Express Plus will be produced. All the newer GNSS products use an entirely different firmware (RTK Everywhere) which is under active development. I’m not speaking for SparkFun… I’m a customer just like you
rftop is correct. The Express Plus is no longer produced. Help me understand: Why do you need an IMU if you’ve got a clear view of the sky? IMUs help with degraded GNSS reception (ie, tunnels).
The situation has changed a bit since a last meeting.
Given that we need to also stream the data from the car back to the person with the VR-set, we plan on installing a 4G/5G router on the car. This enables the use of NTRIP. Reading through the forum, this is a more ‘easy’ setup than always configuring your own base.
That still leaves the choice of rover open. The update rate has become more important than initially thought, which is why we are leaning to the mosaic-X5 (100Hz). All the facet-FP’s only reach 20Hz (even with mosaic-X5 core).
My question is whether the following setup will work, or if I’m overlooking problems. Also, what would be the main reasons to switch to the facet FP instead of the mosaic-X5?
RTK/GNSS sensor on car, receiving RTK corrections over NTRIP from a 4G/5G router.
The sensor sends its position over wifi to a stationary laptop, which processes the data and is connected to the VR-set.
Yes, if cellular is available then NTRIP will make your life easier
I don’t have a RTK mosaic-X5 (designed as a dedicated base station) and I’ve never tested one. I am however slightly skeptical of 100 Hz update over WiFi for your application, with the ESP32-WROVER as the Ethernet-to-WiFi bridge. The X5 module is capable of 100 Hz, but I’m not sure the entire system is (outside of perfect conditions for product specification).
This product has it’s own dedicated firmware so its likely possible. I expect SparkFun can offer some clarity if 100 Hz is realistically possible over WiFi, but the local RF environment will play a factor. The math (packets-per-second, bandwidth, etc) say’s it can work, but the real world always seems to have a curveball for me.
Last thought: Since 100 Hz is now a requirement, then you are looking at the device with the best chance (IMHO). Maybe start with just the RMC sentence and work up from there ?
This will be an interesting and educating discussion either way.
Good luck, I look forward to seeing the outcome if you are able to share
For a 100Hz VR application, I would suggest looking at the mosaic-H (dual antenna) as this would give you better vehicle heading and attitude information in real time.
Sadly we (SparkFun) don’t have a mosaic-H product. But there are several out there.
Have a good think about your requirements and data rates. Will a single UART meet your needs? Or do you need the additional speed of Ethernet-over-USB or true Ethernet? Perhaps you need multiple interfaces, say UART / virtual-UART-over-USB / TCP (over Ethernet) for NTRIP plus another UART / TCP connection to return the position and attitude information to the laptop? The mosaic-H itself supports all these options. The available interfaces will guide you to one vendor solution over another.
My advice would also be to avoid WiFi if possible and use hardwired interfaces for integrity, reliability and known well-understood throughput. The SparkFun RTK mosaic-X5 uses an ESP32 as an Ethernet to WiFi bridge. We do see throughput issues and packet errors when using WiFi to update the X5’s firmware. It works, but it is nowhere near as clean as Ethernet or Ethernet-over-USB.
