This is a full guide for using OxTS Georeferencer to produce pointclouds of your surveys. This will guide you from recording your data to viewing your pointcloud. This guide follows an example of an xNAV and VLP-16 although the principles are the same for any compatible LiDAR device and OxTS INS.
- Set up your INS and LiDAR devices in your vehicle. Connecting them to a power source and to a computer and make sure your IP configurations are correct. Follow this Hardware integration guide for VLP-16 integration
- Measure precisely the angles (yaw, pitch and roll) and distances (x, y and z) between the INS and the LiDAR, using the IMU measurement frame as your datum.
- Check your data streams and logging if you are viewing them in real time.
- Complete your initialisation and warm-up run. To get the best output from your unit you can read here.
- Complete your boresighting procedure if you are doing one. Remember to log this run in different files to a survey.
- Complete your survey run, check again beforehand that your data is logging and in a separate file to your boresighting run. Do another warm-up at the end of the survey if you will use combined processing, you can turn the LiDAR logging off for this.
- FTP to your INS device and retrieve the RD, LCOM and VAT files from your runs.
- Process your raw data file how you want it, with combined processing and RINEX files using NAVsolve to produce your NCOM file. Ensure Local Coordinates are enabled
- Create your LIP and LIR files from your measurements. Use a boresighted LIR file if you made one.
- Drag your NCOM, LiDAR, LIP, LIR and VAT files into Georeferencer and check the journey path in the window.
- Check in the Hardware tab that your configuration is correct and make appropriate adjustments.
- Run Georeferencing to produce your pointcloud.
This section is a brief guide to setting up your equipment to make a LiDAR survey. A full guide for integrating the hardware of a VLP-16 with an OxTS INS device can be accessed here. You will need to place the INS and LiDAR device on or in your vehicle with the LiDAR having an appropriate view. It is very important at this stage that you make sure both devices are secure and do not move during the survey. The next step is to measure the positional and angular offset.
When you set up your configuration you will need to measure the relative distance between the INS measurement point and the LiDAR optical centre. Make sure to do this accurately and that you measure from the measurement point of each device not just the centre of their housings. These measurements include the XYZ linear displacement and also their relative roll, pitch and yaw. This is in addition to the INS-vehicle configuration measurements that NAVconfig requires (VAT file). These measurements won't be needed during set up but note them down for later. If you want centimetre accuracy you will have to ensure the XYZ displacment is accurate to better than a centimetre.
It is particularly convenient to use a fixed mounting if you want to take many surveys and to be more accurate in your measurements. If you have a standard, repeatable configuration your life will be much easier as you only need to take configuration measurements once. CAD files of the LiDAR will be available from the manufacturer and of the INS from OxTS.
Figure 1: A mount that OxTS uses internally. It has a fixed relative position and orientation and holds both devices securely to the vehicle. On the right is a view of the setup that can be seen in Georeferencer.
There are many different ways of setting up your cable connections depending on your preferences. Below, on the left, is a diagram of the setup for taking data. On the right is a selection of choices for viewing data. These are discussed more thoroughly in the next section. You can choose setup 1 or 2 to view both streams of data in real time or setup 3 to see only one stream of data or to setup the INS. Your computer may require USB-ethernet adapters.
Figure 2: Diagram of a device setup. On the left, the setup of cables to run the devices and log data. On the right, setup for viewing data in real time.
If using a Velodyne product, you can use the Velodyne web interface to make some checks. Putting the IP address of the VLP into a web browser will bring up the web interface (see Figure 3), you can check there that the PPS is locked and that there is a real time GPS position (the LiDAR is receiving NMEA data). Additionally, you can open VeloView to see the LiDAR data in real time.
Figure 3: The Velodyne web user interface is accessed by typing the IP address into a web browser tab. Check that PPS is 'Locked' and the GPS Position is updating in real time (and so the LiDAR is receiving NMEA).If you are using two ethernet ports to your computer to view both the INS data and the LiDAR data in real time you will likely need to bridge the connections and ensure all devices are using the correct IP addresses. You will have to configure IP address if using setup 1 or 2 from the above section. This is so the computer can receive both streams of data but also so that the LiDAR can receive the NMEA from the INS and the INS can log the LCOM data. The LiDAR data can be recorded as a PCAP file in VeloView (for Velodyne products) simply by clicking the record button or by using Wireshark.
In NAVconfig > Hardware Setup > LiDAR Scanner, select your scanner type and, if using onboard LiDAR logging, tick the boxes for logging data and logging telemetry. You then have a choice of sending your NMEA data over ethernet or over serial (see Figure 4). The cable connection that supplies the LiDAR with power from the INS also sends the PPS and serial data. NMEA data can be sent over an ethernet connection using a connector, a switch or a network bridge. The default ports should not need to be altered. If you are sending data over ethernet you will need to put the IP address of the LiDAR device in, alternatively you can use the broadcast IP address 255.255.255.255 but this may unnecessarily saturate your network.
Figure 4: Selecting how NMEA data is transferred from the xNAV to the VLP (right highlighted box). Selected scanner type, inputting IP address and data logging settings (left box).
It is important that your INS is initialized while it is taking data, this is because initialization is used as part of the synchronization check. Initialisation is when your INS device locks onto its location and heading. You are able to view in NAVdisplay if your system is initialised or is ready for initialisation. You do not have to begin your survey initialized but at least one third of the time your data file is recording you should be initialized. In NAVconfig > Environment you can set your initialisation settings to use static (requires dual antenna) or dynamic initialisation .
If you are not using NAVsuite 2.8 and you choose ‘Send NMEA over serial 1’ as an option you will need to then go to NAVconfig > Interfaces > Serial 1 Output and ensure that GPGGA and GPHDT are switched off (see Figure 5).
Figure 5: Ensure that the only message transmitting at 1Hz is the GGRMX and that GPGGA and GPHDT are disabled. You won't have to do this if using NAVsuite 2.8.
In NAVconfig > Environment you will need to select ‘Enable local coordinates’ and choose your origin (see Figure 6). This can be done in post-processing in NAVsolve > Process > Local coordinates or by creating an LRF file manually. Doing it before your survey will simplify the processing later.
Figure 6: Enabling local coordinates in NAVconfig, you can then choose your origin.
It is encouraged that you check that the correct data is being logged and to have a trial before starting your survey. You can easily connect the INS to the LiDAR via the INS user cable and when they are connected and configured properly the INS should be automatically taking the LiDAR data and storing it locally as an LCOM file. OxTS offers multiple cable types with LiDAR adapter interfaces, these can be seen in the manual. Version 3 OxTS INS devices can store up to 32GB of raw data (INS + LiDAR).
While taking your data, you may wish to break up your survey into multiple runs. This can be done easily using NAVdisplay. If you are viewing your INS data in real time then you can click in the box at the bottom of NAVdisplay and type "!log log on" and "!log log off" and then click send to stop and start data logging. The RD file will continue to log as it runs in a separate process of the firmware but the LCOM will stop, you can view this happening by using an FTP connection and seeing that the file size does not grow after refreshing. You can use the same RD file for multiple surveys later.
If you open OxTS Georeferencer you will see that you require 5 files in the Files tab. These are an NCOM file, a LiDAR and an LIP, LIR and VAT file (see Figure 7). All of these files are simple to obtain after completing your survey, they can also be available during your survey. You can drag your files from File Explorer into Georeferencer.
Figure 7: The Files tab in Georeferencer showing your 5 files and the NCOM journey on Bing maps.
You will need information about your vehicle trajectory in order to Georeference. This will be in an NCOM file. To obtain your NCOM file you will need to retrieve your raw data file from the INS and then process it into an NCOM. You can FTP to the INS via an ethernet connection and download any files you need, this can be done in NAVsolve, File Explorer or Filezilla and you can then download the files to your computer. In File Explorer type ftp://192.168.1.xxx where the x's are the IP address of the INS (see Figure 8). The time that the data log started is recorded in the name of the file. When you have the RD file you will need to process it, this is done using our NAVsolve software and you can find a guide for processing your RD file here.
Figure 8: Using an FTP connection (ftp://192.168.1.13) to the INS to retrieve the two most recent files in its data. You can use an FTP connection in real time to check that the INS is logging the RD and LCOM file by refreshing the File Explorer window and viewing the file size. The highlighted RD file was created on the 12th February 2020 (20/02/12) at 15:24 as seen in its filename.
The second file you need is a LiDAR file, this can be LCOM or PCAP. An LCOM file can be found on the INS via an FTP connection if you set up your devices for this. If you didn't setup your devices to record LCOM then you will have recorded a PCAP during the survey run via some software like Wireshark or Veloview. You will need to take this file from where you saved it and drag it into OxTS Georeferencer.
The first check that OxTS Georeferencer makes is that the LiDAR data is PPS synchronized and has NMEA data, this will depend on if you have set up the device connections correctly. If the data passes this check you should see a tick. If the file fails synchronization, consider your setup again and check any connections and network configurations you have, you should be able to do this in real time (see above sections). Remember that the INS must be initialised for the LiDAR log to have the required synchronisation. To be able to process your pointcloud the NCOM and LiDAR data must align in time as well. Opening an NCOM in OxTS Georeferencer will show your journey route overlaid on Bing maps to help you check which survey the NCOM corresponds to. If using a PCAP, you will see under the map the time overlap that the PCAP and NCOM data sets have. A pointcloud will be created for the time that the LiDAR and INS data overlap.
The VAT file is the angular configuration of the INS with respect to the vehicle frame. You must put in some preliminary measurements for this when setting up in NAVconfig but the system will intelligently improve the angles throughout the journey. You therefore do not have to make a VAT file yourself. After processing your raw data file the VAT file will be available in the "Process_..." folder created by NAVsolve. The VAT file is a simple text file with a .vat extension.
The LIP file is the positional configuration of the LiDAR with respect to the INS frame. This is the x, y and z displacement from the INS measurement point to the LiDAR device, each of these measurements is on their own respective line in a simple text file with an .lip extension. You can create an LIP file by clicking on the LIP plus icon in Georeferencer and then input the numbers in the Hardware Configuration tab. You should have measured these while setting up and they should be as accurate as possible.
For users used to using commas instead of points for a decimal point separator you must use a point. The next version of Georeferencer will accomodate for comma separators.
The LIR file is the angular configuration of the LiDAR with respect to the INS frame. This is the relative yaw, pitch and roll displacement between the INS measurement axes and the LiDAR device axes, each of these measurements is on their own respective line in a simple text file with an .lir extension. You can create an LIR file by clicking on the LIR plus icon in Georeferencer just like the LIP.
You can make estimations for the correct axes beforehand and then edit them in the Hardware tab of Georeferencer where you can view the configuration. In addition, if you have done a boresighting run, make sure you use the boresighted LIR values. A boresighted LIR file will have a flag value of '1' on a fourth line to signify it is optimised.
Example LIR, LIP and VAT files are available at the bottom of the page.
Figure 9: In the Files tab you can create the LIP and LIR files by clicking the plus icon. The files are then edited and viewed using the Hardware Configuration tab.
Figure 10: The hardware tab allows you to view your configuration and make alterations to the LIP and LIR files.
Boresighting is OxTS’s in-built calibration method. When you make your angular offset measurements they can be quite difficult to make accurately. A small angular error can make a large difference to a pointcloud and potentially lower the quality of your survey. We recommend you boresight your configuration before carrying out a survey; but once a configuration is boresighted it will not need to be boresighted again. Boresighting will make your LIR file much more accurate and prevent blurred images or ‘double vision’ that may occur. A guide for boresighting can be viewed here.
Figure 11: Example comparison of an unboresighted (left) and boresighted (right) LIR (orientation) file. The calibration is able to refine the orientation much finer than it is possible to do by sight.
Figure 12: Example of a pointcloud before (left) and after (right) boresighting.
A useful feature for different applications is the ability to choose the distance range of points that OxTS Georeferencer will turn into a pointcloud. This is done by changing the minimum and maximum parameters under 'Range Between which points will be written (m):' section in Files > Advanced Settings. If you want to only see a road for example and not surroundings far away then you can restrict the range to 0-10m. If you wanted to only see over a certain range, in some geographical application for example, you can set the range to 10-100m.
Many of the advanced settings are achievable in pointcloud post-processing software but due to the large file size it is often more useful to do it during the creation of the pointcloud.
With your 5 compatible files you will be able to click Run Georeferencing. This will create a folder in the directory that the NCOM data is in or where you specify in the Files tab; the folder will contain your pointcloud, the LIP, LIR and VAT used and 2 processing logs.
Georeferencer can create pointclouds in LAS, LAZ (compressed) or PCD formats. This is chosen in the Files > Advanced Settings tab. The default is an LAZ file.
You will now be able to view your cloud in your choice of pointcloud viewing software (eg CloudCompare, QT reader or others). OxTS Georeferencer is available to download and will be available for use with all OxTS systems until September 2020 (feature codes will be required after this point), if you would like example sets of data please get in touch or download straight from the website. We also appreciate you sharing your data with us.
Figure 13: Example of cloud being viewed in CloudCompare after being processed in OxTS Georeferencer.
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