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LPMS-IG1P needs to be installed in the vehicle in a known orientation ideally with the coordinate axes of the IMU arranged in parallel to the vehicle coordinate system. As vehicle reference frame we are using the VW coordinate system shown in the image below. Connect the USB connector of LPMS-IG1P to the host computer. If needed an active or passive USB extension can be used. Make sure to check data integrity with the LpmsControl 2 data acquisition tool, we have noticed communication issues with some passive USB extensions.
See the appendix for further information how to set up LPMS-IG1.
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VW frame x: back y: right z: up |
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Global Positioning System (GPS)
The We provide two options of global position reference:
GPS receiver is integrated with the LPMS-IG1P sensor. Connect the antenna cable and place the GPS antenna on top of the vehicle
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Standalone multi-channel RTK GPS
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receiver module. This requires setting up an RTK-GPS basestation. Details are provided in this chapter.
CAN Bus Connection
FusionHub can be connected to the vehicle CAN bus by using one of the following CAN bus interfaces:
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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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The following is an excerpt from the Emlid RTK-GPS base station documentation. We’ve added it here for convenience and because it explains the principle of RTK-GPS in a very instructive way. Please make sure to check the original documentation here. |
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GNSS receivers measure how long it takes for a signal to travel from a satellite to the receiver. Transmitted signals travel through the ionosphere and atmosphere and are slowed down and perturbed on the way. For example, travel time on a cloudy day and in clear sky conditions would be different. That is why it is difficult for a standalone receiver to precisely determine its position. RTK is a technology that solves this issue.
High real-time precision
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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Corrections over NTRIP
You do not necessarily need a second unit for RTK all the time. Usually, there are local services that share base corrections over the Internet. This technology is called NTRIP.
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:
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Autonomy in remote areas as there’s no need in the Internet connection
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The correction data is sent from the base station to the rover as so-called RTCM data packets, that are sent using the NTRIP protocol. Base and rover are connected via a caster service, that relays the data from the base to the rover.
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 could be used, or you could even easily set up your own caster service.
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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. |
Components
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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:
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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.
References
Emlid Reach RS2+ documentation
Ublox ZED-F9P module documentation
Appendix
LPMS-IG1 Setup
General documentation for LPMS IMUs is here.
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