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The IMU sensor can be mounted in any way but the ImuToCarRotation quaternion needs to be provided to transform the IMU data into VW frame. For example, if the IMU is mounted like follows:
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Communication with External Applications
There are multiple ways that LPVR-POS can communicate with external applications:
WebSocket APIs
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Connect via WebSocket API to FusionHub WebSocket server to configure FusionHub node parameters and to stream data to a client application. This method is being used by the FusionHub frontend application.
Stream data to a client application via JSON / Protobuf-encoded ZeroMQ. This method is used internally by FusionHub to connect its various nodes. Each output node can be configured to stream data not only internally but also externally.
Forward pose data to a client application such as the Unreal Engine via VRPN. This is in many cases the easiest way of streaming data to a client, but it is not as flexible as using the Websocket API or ZeroMQ.
WebSocket APIs
Apart from manual editing the config.json configuration script or modifying it through the GUI, FusionHub also offers a WebSocket API for external applications to change its configuration. The GUI uses this interface to access FusionHub’s settings.
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RTK is a technique used to improve the accuracy of a standalone GNSS receiver. Traditional GNSS receivers, like the one as used for instance in a smartphone, could can only determine the device’s position with 2-4 meters (7-13 feet) accuracy. RTK can give you centimeter accuracy.
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Two receivers are used in RTK. One of them is stationary, another moves freely. They are called base station and rover.
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The base's mission is to stay in one place and send corrections to a moving receiver. Rover uses that data to achieve centimeter precise position. Any number of rovers can connect to one base if their input settings match the base's output.
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NTRIP is a good option for areas with strong 3G/LTE coverage and a vast network of NTRIP bases nearby. In other cases, using the second receiver as a local base station has two advantages:
autonomy Autonomy in remote areas as there’s no need in the Internet connection
independency Independency from local providers, no additional fees by NTRIP service
For LPVR-POS we use a free NTRIP caster service provided by the company Emlid. The caster service handles the NTRIP communication between base station and LPVR-POS in the car, without the need of these systems knowing the IP address of each other. Besides the Emlid caster, alternatively another caster service
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could be used, or you could even easily set up your own caster service.
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How to Set-up RTK-GPS for LPVR-POS
In the case of LPVR-POS the above-mentioned rover is the vehicle that contains the computer running LPVR-POS is running in. To enable GPS with centimeter accuracy, we need to install a base station in a fixed location in the vicinity of the vehicle, or alternatively use an available NTRIP service. We will focus here on setting up a base station as it is in this way wer are location and infrastructure independent.
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Note that both, the base station as well as the vehicle need to be connected to the internet in order to make communication between the two work. You can directly insert a SIM card into the Emlid RS2+ base station that we optionally provide with LPVR-POS. |
In order to set up an RTK GPS system to work with LPVR-POS follow the below steps. You need to do these steps only once, after that the system should be ready to work when you turn it on:
Set up an NTRIP caster service by creating a free Emlid Flow account. Note that you only need the free version.
Set up the Emlid RS2+ base station. A detailed guide how to connect it to the internet using a SIM card and adjust its settings is here: https://docs.emlid.com/reachrs2/rtk-quickstart/connecting-reach-to-the-internet/enabling-cellular-modem
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Once you successfully connect your base, you will see the ONLINE notification next to the mount point name.
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Once you successfully connect your roverstart FusionHub and it successfully connects to our NTRIP caster, you will see the ONLINE notification and the number of the connected rovers in the My rovers section.
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FusionHub should now output the status of the RTK-GPS connection to the command line. Note that currently we don’t yet output the status in the GUI. This will follow soon. There three states to the RTK-GPS system:
GPS (RTK not connected, output has normal GPS accuracy)
Float (RTK connected and working, but not enough data to get high accuracy output)
Fix (RTK connected and in high-accuracy mode)
Preferably we always want the system to operate in Fix mode. This requires working connection to the NTRIP caster, decent antenna placement and a sufficient number of satellites in view of the car’s antenna and the base station antenna.
As for LPVR-POS we are using a multi-channel GPS system, performance should be relatively robust. Check the output of the Emlid software to check the number of satellites the base station is seeing.
If you managed to get an RTK-GPS fix, your LPVR-POS system is now ready to operate with RTK-GPS as global centimeter-accurate position reference.
Appendix
LPMS-IG1 Setup
General documentation for LPMS IMUs is here.
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