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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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Sending FusionHub Data to External Applications via the ZeroMQ Interface
FusionHub emits the data resulting from the sensor fusion through the local network interface.
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The network port that this information is output to can be configured in the JSON parameter file config.json of FusionHub. Usually each FusionHub node contains a parameter setting such as "endpoint": "tcp://*:8899" that allows settings the output port. The output from the node can then be accessed by connecting to the IP of the computer that FusionHub is running on the defined port.
Data Format
As low level protocol to emit the output data we use ZeroMQ (publisher / subscriber). The data itself is in JSON format and is encoded as Protocol Buffers. Protocol Buffers are documented here. Message are defined in the Protobuf (.protoc) format as defined in the file stream_data.proto. This file is contained in the installation folder of FusionHub.
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Download a Python example that shows how to decode messaged messages from FusionHub from this repository.
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Apply the output from the fusion hub to an Unreal object eg. a cine camera actor.
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RTK-GPS Setup
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Overview
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| Info |
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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 RTK-GPS in a very instructive way. Please make sure to check the original documentation here. |
RTK is a technique used to improve the accuracy of a standalone GNSS receiver. Traditional GNSS receivers, like the one in a smartphone, could only determine the position with 2-4 meters (7-13 feet) accuracy. RTK can give you centimeter accuracy.
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:
autonomy in remote areas as there’s no need in the Internet connection
independency from local providers, no additional fees by NTRIP 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 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 location and infrastructure independent.
| Info |
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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. |
In order to set up an RTK GPS system to work with LPVR-POS follow the below steps:
Set up an NTRIP caster 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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Next, adjust the base station settings so that the base station outputs correction data to our NTRIP caster: https://docs.emlid.com/reachrs2/rtk-quickstart/base-rover-setup Note that we only need to follow the instructions on setting up the base station, the rover we set up via the FusionHub interface.
Configure the base station to talk to our Emlid Flow account: https://docs.emlid.com/emlid-caster/emlid-caster-base-rover-connection
Set up FusionHub to receive RTCM data from the Emlid Flow caster:
For example if your caster configuration is the following:
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Set the parameters in your config.json to the following:
| Code Block |
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"RTCM": {
"type": "NTRIP",
"settings": {
"host": "caster.emlid.com",
"port": "2101",
"mountpoint": "MP...",
"user": "u49528",
"password": "796dqw",
"userAgent": "LPVR",
"initialLatitude": 35.65736,
"initialLongitude": 139.73239,
"forwardGnss": true
}
} |
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 rover, you will see the ONLINE notification and the number of the connected rovers in the My rovers section.
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Appendix
LPMS-IG1 Setup
General documentation for LPMS IMUs is here.
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