RT-Range technical note

RT-Range – an introduction to OxTS’ comprehensive ADAS testing solution

August 15, 2016

The RT-Range is a powerful system that has been designed to work in conjunction with our GNSS-aided inertial navigation products. Its main function is to produce real-time distance measurements between itself and other objects such as cars, pedestrians or lane markings. Those measurements can then be used to monitor things like time to collision, relative position or even visibility. The system is used extensively in the automotive industry for the test and validation of ADAS technology, but has many other applications.

There are two types of RT‑Range. The Hunter version is the main product and can be considered the key component; thanks to its powerful processing capabilities it’s where all the data is collated and where measurements are calculated and output. In contrast, the Target version of the RT‑Range is a much simpler device and exists only to collect and transmit information back to the Hunter for processing.

How does the Hunter know where it is?

RT-Range Hunter components

Before any measurements can be calculated, the Hunter must know where it is and how it’s orientated. This information is typically gathered by linking it to one of our GNSS-aided inertial navigation systems—such as an RT3000. Once connected via a simple ethernet interface, the precise position, orientation and velocity measurements produced by the RT3000 are available to the RT-Range Hunter.

How does the Hunter know where the Targets are?

The Hunter knows its own location at all times thanks to the information supplied by the inertial navigation system (INS) it is connected to, but in order to calculate measurements to Targets, it must know where they are too. The Hunter gets this information in one of two ways depending on the type of Target being tracked. Three different types of target can be tracked as shown below:

  • A fixed point target (real or virtual) is used to identify an object that will remain stationary for the duration of a test. Fixed point targets are simply defined by latitude, longitude, altitude and heading—allowing the Hunter to easily compare its own position to theirs. Examples of fixed point targets includes street furniture and parked vehicles.
  • A mobile target has the potential to move, even though it may not. In order for a mobile target to know its own position and orientation it must be fitted with an OxTS RT and an RT-Range Target. Once the position information is sent back to the Hunter via wi-fi or radio modem, it can be used to calculate measurements to the Target. Examples of mobile targets are cars, pedestrians, motorcyclists and other vulnerable road users.
  • A feature point is actually a file containing the latitude, longitude, altitude and heading of up to 65,000 individual points. The Hunter compares its own position with that of each point. However, instead of interacting with each point in the file continuously (like fixed points), the Hunter only interacts with feature points when they fall within a specific area called the field of view. This makes a feature point ideal for testing vision-based systems that need to selectively interact with a large number of points. Examples of fixed point targets includes street furniture and parked vehicles.

 How are measurements calculated?

When using the most basic settings, RT‑Range measurements are calculated from a specific point on the Hunter to a specific point on each Target. The point on the Hunter is referred to as the sensor, while the point on each Target is called a bulls-eye. By default, the sensor and each bulls-eye have zero offset. This means they are located at the measurement origin of the local INS (in the case of Hunters and mobile Targets), or at the point specified by the lat/lon/alt of fixed points and feature points. However, in real-world applications, an offset is often required to move the sensor and bulls-eye points to a location on the perimeter of the vehicles being tested.

Applying an offset to the sensor or bulls-eye

The RT‑Range Hunter is configured using the RT-Range software. To access the configuration software panel:

  • Launch the RT-Range software
  • Select the Real-Time Display button
  • Select Configure RT-Range

Note: it is not necessary to be connected to a live RT‑Range in order to create a configuration as they can be saved to disk and committed to the hardware at a later date.

Sensor and bulls-eye offsets are defined under the range measurements page as shown below (select range measurements from the left-hand navigation bar). Sensor offsets are defined in the vehicle frame and originate from the IMU measurement origin, not from the Hunter.

RT-Range software Hunter

Once a fixed point or mobile target is added in the Hunter/Targets setup page, additional tabs will appear next to the Hunter tab where the bulls-eye offsets for those targets can be entered. Target tabs will not appear for feature pPoint targets as no offset can be entered for that type of target.

RT-Range offset

A separate document explains how to define the Hunter and Targets as polygons. Setting up polygons is useful in many ADAS applications where it is necessary to calculate measurements between the nearest point on two objects regardless of their relative position and orientation.

The image below shows how a Hunter will calculate measurements to a mobile and fixed point Target. The bulls-eyes on the mobile Target has been offset, as has the Hunter’s sensor.

RT-Range static and mobile target

The location and heading of each INS is show by the red square. The sensor offset on the Hunter is shown by the dotted line; there is only a longitudinal offset in this example. On the mobile Target there is also a longitudinal offset from the INS measurement origin to the bulls-eye. On the static Target there is no offset, so the bulls-eye is centred on the latitude/longitude used to define the static Target. The RT-Range measurements, originate from the sensor to each bulls-eye. As the Hunter and mobile Target vehicles move, the sensor and bull-eyes maintain their relative position to the INS mounted in each vehicle.

While this article gives a taste of the comprehensive features of the RT-Range, there are many more. To find out more about the OxTS RT-Range, contact us today.