This is a guide to completing a survey with an OxTS INS device. It will help you with setting up and using your device, completing your survey and processing your data. Links to other support guides will be provided that cover different parts of the workflow in more depth.
Survey workflow summary:
- Collect all of the correct equipment for your application: e.g. xNAV, 2 antennas, 2 antenna cables, laptop, ethernet cable, (ethernet-USB adapter), xNAV user cable, survey equipment and vehicle.
- Set up your equipment on your vehicle ensuring you have considered baseline, multipath, vibrations and movement etc.
- Configure your device. Power the INS up and connect it via ethernet to a laptop or PC and open NAVconfig. Input the measurements you need. If this is not possible, measure all of the measurements now and you can make a configuration file after the survey although it is highly recommended to get it right at the start.
(Measurements needed: INS device orientation with respect to the vehicle, position of the primary antenna with respect to the INS, position of secondary antenna with respect to the primary, height of the INS above the ground, position of the centre of the rear axle (if applicable) with respect to the INS, position of the centre of the front axle with respect to the INS device, position and orientation of survey device with respect to the INS)
- You can now power the device down. Move to the area you wish to survey. Power up the device again.
- Initialise your device and perform a warmup.
- Complete your survey.
- Perform a warmdown.
- Retrieve your files from your device(s) and process your RD files into NCOM files using NAVsolve.
- Analyse your data.
Before heading out you will need to have all of the necessary equipment.
- INS Device: Collect your xNAV, Survey+ or xOEM device depending on your application.
- Surveying Device: Collect your surveying devices, relevant power connections and cables for connecting them to your INS.
- Antennas: Collect your antennas. Ideally you will have two unless your application can only use 1 antenna. Remember to collect the suitable cables for connecting the antennas to the INS.
- Laptop: This is not necessary for many applications but it makes it easy to check that everything is working correctly and can save time so it always recommended where it is possible. Make sure you can connect to the INS, this requires an ethernet port, if you do not have one then a USB-ethernet adaptor will be needed. Ensure you have enough battery and/or an appropriate charger and that all necessary software is installed and updated. Latest NAVsuite.
- Power supply: You will need a power supply compatible with both the INS and survey device. The 12V from a car battery through a cigarette lighter port is usually sufficient. A different power source may be ideal if the engine is likely to cut out. xNAVs and xOEM devices run on 10-31V power supplies and the Survey+ runs on 10-48V. Consider what cable interfaces the power supply requires and what the user cable may handle.
- User cable: You will need the user cable for your INS to provide power to it and to connect to other devices and the laptop.
- Mounting units: You will likely need some way to mount the devices on the vehicle and you will have to consider how to do this. An example suction cup mount is shown below.
- (Boresighting targets): If you intend to perform a boresight calibration then you will need suitable targets. These should be square, flat targets (wooden boards will do) roughly 80x80cm and covered with reflective material (retroreflective tape is suitable).
This section will take you through setting your equipment up. There are many considerations to take into account but in general you can follow the following points.
- Consider several things: Make sure the survey device is in a suitable position to survey and set up around that. Think about how to make the baseline (distance between antennas) as large as possible. Consider vibrations, the way you set up may trigger vibration in the devices and this is not desirable. Consider multipath, this is when a signal from a satellite can hit your antenna from beneath or after reflecting off of the ground. Consider any EMI sources, keep these away from the antennas if possible.
- Place your INS device and survey device securely onto your vehicle. Ensure that they cannot move relative to each other - they must be rigidly connected together and this should not move relative to the vehicle at any point while in use. If you are using a Survey+ you might want to use an OxTS RT-Strut. Ideally some bespoke mount will be created that rigidly hold the surveying device and INS and mounts securely to the vehicle. Ensure that cables can reach each device and the surveying device is able to view the environment and does not view the vehicle.
A further consideration is that of vibration. Some damping methods may be necessary although there are some ways to mitigate vibration in OxTS processing.
- Set up your power supply. Ensure that it will not cut out at any point during the survey and that cables from the devices can reach it.
- Set up your antennas. It is important that you have them as far away from each other as possible. You may place them at the front and back of the roof of a van or on a long bar mounted to a UAV for example.
Make sure that GNSS signals cannot hit your antennas from underneath; this may be the case if the surface is glass. Ensure that the antennas have the orientation (within 15°).
- Connect up all the devices and antennas. Using the antenna cables, survey device cables and INS user cables connect up all your devices. Ensure the INS and surveying device have power and the antennas are connected to the INS correctly (your primary antenna connects to the primary antenna port) and it is likely you will need to connect the INS to the survey device (using the user cable this can be done by serial or ethernet). You can also connect the INS to the laptop for the next step.
The next thing to do is configure your INS device and check the surveying device. Often a surveying device will have a way of interfacing with it using a laptop connection and on the manufacturer's software or web interface you can check the settings for it. It is not strictly necessary to connect to the INS to configure it, this can be done afterwards but it is recommended to do it at this stage. Consider how the surveying device will log its data. The INS has 32GB of storage that can be used. Check that your surveying device is logging data correctly and it has the time sync (PPS) and navigation NMEA data.
You will at least need to make the necessary measurements which are: the INS device orientation with respect to the vehicle, position of the primary antenna with respect to the INS, position of secondary antenna with respect to the primary, height of the INS above the ground, position of the centre of the rear axle (if applicable) with respect to the INS, position of the centre of the front axle with respect to the INS device, position and orientation of survey device with respect to the INS. Make these measurements as accurate as possible, in general they must be within 10cm of the reality and remember to measure from the measurement point of the INS.
To configure your device, make sure it is powered up and connected via ethernet to the laptop.
- Read Configuration: Open NAVconfig and the device IP address should be viewable automatically on the Read Configuration section. Select the device and select the vehicle type and proceed to the Hardware Setup section.
- Hardware Setup: This is where you input all of your measurements. You can wait until now to do the measurements and input them in order. It is likely the 'GNSS Differential Corrections' tab will not need changing unless you wish to use SBAS. If you are using a LiDAR scanner then you use the 'LiDAR scanner' tab. Here select the scanner, select to log data and telemetry and if you are connected to the LiDAR via ethernet or serial. You will need to put the IP address of the LiDAR. A more detailed guide to setting up for LiDAR can be found here. Proceed to the Interfaces section.
- Interfaces: You will likely not need to change these settings. If you are using a survey device such as a camera that needs to have a trigger to take a picture then you can change these settings on the 'PPS / Triggers' tab. Proceed to the Environment section.
- Environment: Here you must choose how you want to initialise (see next section in this guide), you can choose to initialise statically or dynamically and at what speed. Generally, if you are using a UAV you will use static initialisation and if you are using a land vehicle then you will use dynamic initialisation at 5-10m/s. You can also tell the device how much vibration it should expect. In addition you can add local coordinates which are necessary for using OxTS Georeferencer.
- Advanced Tools: Advanced tools are unlikely to need changing. You may wish to select the output lock feature in the 'Output Lock' tab. You can select here to use OxTS gx/ix or the GNSS receiver's own calculation. Another point is on the 'Displace Output' tab. This can be used with cameras or other devices to displace the output position of the INS to the survey device's position. Do not use this if you are using a LiDAR with OxTS Georeferencer. Finally, you can change the coordinate system you are working in on the 'Global Coordinate System' tab. The default is the WGS84. Proceed to the Write Configuration section.
- Write Configuration: Commit the configuration you have just written to the device with the 'save changes and reset the device' option.
You may wish to stay connected to the INS and to open NAVdisplay so you can view the diagnostics of the device.
A detailed guide to using a LiDAR device with your INS can be found here.
Your device will need to warmup before it can be used to spec. A support article on why a warmup is important and how important it is can be found here. Take your vehicle to a suitable location to perform a warmup and power up the device. A warmup takes 15 minutes to get to the full abilities of the device which should be better than the specification given however a few minutes of warming up is often all that is needed.
Initialisation: An initialisation must be carried out every time the device powers up. Getting the initialisation right is important and your manoeuvers cannot be redone in post-processing. If you have selected static initialisation then the device will start looking for a lock on its position and heading immediately after booting up and this will take about a minute. Make sure you have maximum satellite visibility for this and you do not crowd around the antennas while it is initialising. If you have selected a dynamic initialisation then make sure you drive in as straight a line as possible until the threshold speed is realised.
The same raw data with different initialisation settings (left is the correct settings and on the right are incorrect initialisation settings).
How long do I have to do a warmup for?
There is an initial warmup of 15 minutes and following this each standard warmup only needs to be 2-5 minutes. This applies if the setup doesn’t change.
In more detail: After powering up the unit, an xNAV unit will typically take 2-5 minutes to warm up depending on the precision of the configuration and the GNSS conditions, this is after a single-time initial warmup of 15 minutes. The warmup time also depends on the level of precision you require. Doing this full warm-up will allow the xNAV to often exceed the specification that OxTS state for it but 5 minutes can achieve decent accuracies and precision. Making more precise configuration measurements to begin with will make warming up faster too.
The xNAV warms up faster than the Survey+ due to the different IMU used but again 15 minutes the first time followed by 2-5 minutes every time the unit is powered up will be enough to achieve the full specification or better.
With an improved or 'tightened' configuration the warmup will take 2 minutes or less.
What is the warmup procedure?
Generally, the procedure for the best possible data is as follows:
- Set-up: Set up your device and take the measurements that are needed for NAVconfig. That is, the position and orientation of the antennas with respect to the INS device and the INS to the vehicle axes. These can be within a few centimeters and the INS will itself correct the values you give it.
- (Recommended): Use NAVdisplay to monitor the progress of your warmup. More information is given in the next section on how to use NAVdisplay.
- First warm-up: When you are happy with your measurements and you are powered up you can start the warmup. We recommend 15 minutes for achieving the full specification or better and there should be good GNSS conditions (open-sky with few obstructions). This will only need to be done once as long as you maintain the same configuration (ie don’t take the INS out of the car or off the UAV).
- Improve Configuration: After 15 minutes of doing manoeuvers typical of the dynamics you will do when surveying you can open NAVconfig and click Improve Configuration. The INS will use the warmup dynamics to improve the measurements that you gave it to a much higher precision. You can monitor in NAVdisplay the progress of the warmup, the accuracies of each measurement will be shown and should get more precise over the warmup duration.
- Roll precision: If you care about absolute precision you can improve the roll precision manually. The car is unable to improve this as there isn’t a no-roll point on the car we can utilise. To improve roll precision open NAVdisplay and come to a stop and view the roll angle that is stated. Drive out and come to the same spot but facing the opposite direction and view the roll again. Your roll offset (the error in your roll measurement) will be the sum of the two roll angles divided by two. This can then be added to the roll angle you set in NAVconfig.
- Subsequent warm-ups: Each time you come to use the unit again after powering it off or resetting it you should do another warmup; this warmup will only have to be a couple of minutes. As long as you have not changed the original configuration this warmup will not have to be long.
- You can start a new file for your survey or in post-processing you can split up the file if you want the warmup separated from the survey.
What dynamics are needed for the warmup?
Typically, you need to have dynamics that are representative of the manoeuvres you will be doing when using the device. The warmup therefore does not need to be excessive.
For land vehicles, we recommend doing figures-of-eight of various sizes, driving in circles clockwise and anticlockwise (this helps roll accuracy), driving in straight lines at constant speed (this helps heading accuracy) and doing various accelerations and brakings (this helps pitch accuracy).
For UAV vehicles the principle is the same, figures-of-eight at various angles, ascensions and descensions and accelerations and stops will be used for a warmup.
Why do I have to do a warmup?
A good warm up is important to ensure that your OxTS product is producing precise, accurate and reliable data.
For an INS to reach optimal specification - the Kalman filter (algorithms that it uses to refine its predictions) needs to account for a number of factors; sensor stabilisation, correcting GNSS antenna and IMU position and mounting misalignment. The Kalman filter also accommodates for device-dependent unknowns such as the age of the device (the device moves away from calibrated settings over time) and temperature (sensors are temperature-sensitive).
The Kalman filter compares and puts together the IMU and GNSS data, it therefore needs open-sky conditions for good GNSS data and a decent warmup to understand the IMU.
Troubleshooting the warmup
It may be that after clicking 'Improve Configuration' you get values that are clearly wrong. When the INS is improving settings it uses the measurements that you give it with a certain tolerance (for example 10cm), it will look within that tolerance for the improved values. If your original measurement was too far out then it may change other measurements to wrong values to find the best possible match. If this occurs the two best ways of troubleshooting are remeasuring and making sure that your measurement is correct and as accurate as possible and also relaxing the tolerances within which the INS searches, this is done in NAVconfig.
After setting up and doing a warmup you are now in a position to start the survey. Every time the device starts up it will start logging automatically with the configuration that it had the last time it was up. Get in position to start your survey and initialise your device following this with a short warmup (2-3 minutes) if possible.
Boresighting: If you plan to use our boresighting calibration solution then you can do the boresighting procedure now as part of the survey run, alternatively; you can do the boresighting run separately as long as the setup hasn't changed at all between that and the survey.
Monitoring: It can be useful to use NAVdisplay and an FTP connection to the device throughout the survey. An FTP connection allows you to see the files that are currently logged on the device and to download them when you want. This allows for flexibility in how you split parts of your survey into different files. Opening the device in NAVdisplay is helpful for viewing if the system is working in spec. Here you can view the accuracies of different measurements and if they are as they should be. The INS device itself will display some diagnostics through the LEDs mounted on the front.
After finishing your survey do a short set of manoeuvers at the end for 2 minutes just like the warmup at the start for maximum performance.
A Brief Guide to NAVdisplay:
NAVdisplay has a huge range of tools for viewing navigation data in real time. OxTS is the benchmark of the automotive industry and so our products are used by test engineers in real time to test safety criteria; it can therefore look foreboding but it is relatively simple. Having NAVdisplay open is especially helpful during the warmup period to check everything is working properly although it isn't necessary it is recommended.
- Starting: Open NAVdisplay and you should be asked to choose which device to view automatically and you can select your device. You can select 'Performance' along in the bar at the top for all the measurements that you will need for a warmup and likely your survey too.
- First checks: Make sure your antennas are the correct way round by viewing the heading and checking that it is roughly correct (point your vehicle North and check that it is (360° or 0°) for example.
- Warmup monitoring: You can see the accuracies of various measurements (heading accuracy, roll accuracy, pitch accuracy, velocity, position north and east accuracy) and these should get better throughout the warmup. Monitoring this allows you to warmup until you are happy with the accuracies. Eventually the accuracies should be better than the specifications. If your accuracies are not getting better then it is likely that one of the measurements is incorrect and you can change it or change the tolerance on it in NAVconfig.
- Survey monitoring: You can see the diagnostics for satellites on the left side of the 'Performance' template. If you are using a RTK corrections in real time and using gx/ix then you should see 'gxInteger' as the position mode for the best data and 6 or more satellites being used. If this does not occur and the environment does not appear to block satellite signals then you should check your antenna setup.
Retrieving files: The files that are logged on your device can be retrieved by an FTP connection. 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 screenshot below). 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. This will give you an NCOM file. If you are using Georeferencer you will also need the .vat file found in the ConfigurationFromRawData folder.
A brief guide to NAVsolve:
A more extensive guide can be found here.
- Open NAVsolve to the Source section and choose 'Select raw data from a folder on your computer' and navigate to the folder that you have the RD file in. Select the RD file and then move to the Preview section.
- Here you can view various diagnostics of your data and see a trace of where your survey took place. Move to the Process section.
- This is where you choose options for processing your data into an NCOM. You can click 'Review configuration' to update any of the measurements or settings you made when configuring the device earlier. Alternatively you can do that all now if you have the measurements on hand. We recommend you choose 'combined' processing if you remembered to do a short warmdown at the end of your survey.
- If you did not add local coordinates to your configuration when configuring and want to then you can do that here on the 'Local coordinates' tab.
- On the 'Base station' tab you can add base station RINEX files if you used your own base station and heave them or you can use public stations. If using public stations you can click search for them to automatically come up. Choose as many as are needed, only the most relevant base stations will be used in processing. A base station is needed to achieve centimetre-level accuracy.
- On the 'Advanced settings' tab we recommend you select 'Advanced smoothing'. Select 'Process'.
Useful NAVgraph tools:
You now have your NCOM and can view it in NAVgraph. Here you can see all of the measurements at all times in the survey and the accuracies thereof. You can crop the NCOM into smaller files here to represent different sections of your survey. You can also export different sets of measurements into CSV files for different uses.
- You can choose what diagnostics and measurements to see by right-clicking the table and clicking 'configure table' and then 'Add Measurements'.
- Create a cropped file by pressing 'r' and selecting the time frame you want.
- To view different measurements on the graph right-click and select 'configure graph' and you can select what measurements are shown. Remember to select a different axis for a different type of measurement.
- After selecting the relevant measurements for your graph you can export these into a CSV file by right-clicking and choosing 'Export' and then 'Binary file format'. You can also create a KML file which will give a trace of your journey that can be overlaid on Google images.
If you are using a LiDAR device and OxTS Georeferencer then you can follow a detailed guide for that workflow here.
- Your configuration only needs to be boresighted once as long as it remains as it is and the LiDAR does not move relative to the INS
- OxTS Support is dedicated to helping you get your solution working, you can email them using the address below
- Using NAVsolve
- A full guide to using Georeferencer
- Optimising the output of your INS
- Further detail on RINEX files and differential corrections
- Accuracy of longitude and latitude measurements
- Introduction to the boresight calibration webinar
- The benefits of gx/ix processing webinar
- An overview of what gx/ix is
- Using 'Displaced Output'
- Setting a local coordinate system
- Advantages of using multiple satellite constellations in urban environments
- Performance test in GNSS outages
- The importance of a warmup
- Performing a boresight calibration (you must be signed in)
- email@example.com for technical support with using OxTS Georeferencer and taking your survey data
- firstname.lastname@example.org for sales enquiries
- email@example.com for data sets or information
- firstname.lastname@example.org for further questions on the survey process or products contact Survey and Mapping product engineer Jacob Amacker