Optimising RT data collection

1: Introduction 

This guide outlines the steps required to ensure accurate RT data collection:

• Accurate INS configuration measurements
• Ensuring high heading accuracy
• Proper initialisation
• Thorough warmup
• Applying improved settings to the configuration

2.1: INS configuration measurements

During installation, configure the following settings:

• IMU orientation
• Primary antenna position
• Secondary antenna position
• Lateral no-slip (IMU position in relation to the centre of the rear axle)
• Vertical no-slip (IMU position in relation to the centre of the front axle)

All measurements must be within the chosen accuracy range in NAVconfig (default is 10cm) for accurate data collection.

2.1.1: Hardware installation

When setting up antennas, ensure the following:

• 1m minimum antenna separation 
• Clear any obstructions around the antennas
• Ensure antenna cables exit in the same direction  
• Mount antennas on a metal surface with a minimum radius of 10cm to counteract multipath signals

2.2: Initialisation types

Dynamic initialisation is preferred because it allows the RT to initialise while moving, ensuring accurate heading results with much higher precision than static.

Dynamic initialisation -  Be sure to drive in a straight line when the initialising speed (default set to 5 m/s) is achieved. If the vehicle is not driven in a straight line, the initial heading calculation will be wrong, causing errors throughout data collection.

Static initialisation - RT should begin initialisation once both antennas receive a consistent signal. Static initialisation can only be performed with a dual antenna set up and should only be done in areas with good GNSS signal and open sky conditions.

2.3: GNSS differential corrections

Without differential corrections, expect a position accuracy of around 1.5 meters. When using corrections, the positional accuracy improves to around 1cm - 2cm when integer level is achieved (gx/RTK). There are several ways to apply differential corrections:

• SBAS (Satellite Based Augmentation Systems) (not recommended as it is not available worldwide and only compatible with GPS)
• Local base station (internal NTRIP client)
• Network DGPS corrections
• RINEX (only for post processing)
• Terrastar (PPP) (only suitable for NovAtel units)

2.4: Warmup

After initialisation is complete, a warmup process should be performed to further refine the RT to achieve optimal specifications using an algorithm known as the Kalman filter. Several factors need to be accounted for by the RT's Kalman filter, including antenna position, IMU orientation, sensor stabilisation, and RT mounting misalignment.
 

Warmups include driving in various manoeuvres to excite the IMU in all directions for around 15 minutes. Hard acceleration and deceleration, as well as driving in circles and figure-of-eight patterns, providing input to the IMU, allowing the unit's Kalman filter to calculate errors in antenna position and IMU orientation filtering them out.

Warmups are also used to correct RT mounting misalignment by reducing the slip offset caused by misalignment between the IMU's perceived heading and the direction of travel, which allows the RT to gather precise data.

During the warmup, all parameters are displayed in real time using the warmup template in NAVdisplay, which is located in the default templates at the top of the window.

Improved settings must be applied via the improve configuration option in NAVconfig. You will be given the choice to select the device in use and which parameters you want to improve: 

• IMU orientation
• Primary antenna position
• Secondary antenna position
• Wheel speed sensor position (can remain unticked if not needed)

The improved values and accuracies should be generated, If satisfied with them, the new values and accuracies can be committed to the RT. After that, reset the device so that the new configuration takes effect.

For optimal data collection, it is advised to carry out a brief moment of dynamic motion after stationary periods.