Where will positioning take us next?

Several positioning technologies are commonly used in off-highway applications. Fleet management systems use GPS to track the location and movements (or lack thereof) of tractor-trailers, service trucks and other vehicles. Some advanced machine control systems used on earthmoving, grading and mining equipment also use GPS in combination with an inertial measurement unit (IMU). Distance measurement instruments (DMIs), commonly known as odometers, are used to record the distances covered by commercial vehicles for tracking maintenance needs.

Individually, the three positioning devices have greatly improved productivity and efficiency. Combined, these same positioning technologies have been used to develop a new system with unique functions—the mobile mapping system (MMS).

Mobile mapping systems are designed to be mounted on a car, truck or other vehicle with two rear wheels. They collect digital data that includes the route of the vehicle; millions of x, y, and z points from laser scanners; and images from camera systems.

The development of an MMS by Topcon Positioning Systems Inc. (TPS), Livermore, CA, was driven by the needs of Internet map data providers. These companies require mobile data collection systems that can efficiently collect geographic information and images on a global scale. Over the past three years, TPS has expanded on the OEM systems to create two commercially available mobile mapping systems: the IP-S2.1 and the IP-S2.2 HD Mapper.

Vehicle positioning devices

The operation of mobile mapping systems is best explained as the integration of two subsystems: vehicle positioning components and information sensors. Three positioning technologies are used to establish the location and orientation of a vehicle as it moves along the surface of the earth:

GNSS receiver and antenna: GNSS includes GPS plus the satellite systems established by Russia (GLONASS), the European Union (GALILEO), and China (COMPASS). It will also include all future systems that go into orbit around the earth. GNSS establishes the vehicle’s horizontal (x,y) and vertical (z) position on the earth to a certain degree of accuracy.

IMU: IMUs are typically used to track motion vectors of airborne objects (airplanes, missiles). The motion paths are known as roll, pitch and yaw.

In a mobile mapping system, simply knowing an x, y, z position on the earth from GNSS is not enough information to align sensor data to the vehicle’s trajectory. During a data collection mission with an MMS, it is possible to temporarily lose GNSS signals or encounter a degradation of the signals due to sky view obstructions. Since IMU’s operate continuously without interruption, they provide supplemental tracking information to the MMS.

DMI: TPS’s systems use two DMI’s on the rear wheels, enabling extrapolation of direction or heading information. In mobile mapping systems, DMIs contribute to the processing of a vehicle trajectory and help in solving any gaps in GNSS by providing motion or path related information.

Data sensors

The typical MMS used for geographic mapping uses laser scanners and digital cameras to collect information along the vehicle trajectory.

Laser Scanners: Laser scanners operate on a principle known as LiDAR. Laser scanners produce millions of x, y and z points, known as point clouds.

Digital Cameras: While laser scanners provide geospatial positioning information for objects mapped along the vehicle trajectory, it is also useful to have images of the area for visual recognition. Single cameras can be configured in arrays to cover specific angles of view.

TPS’s mobile mapping system uses a camera with six CCDs and lenses in one housing. During data processing, the images from the individual cameras are stitched together to create a single 360 degree panoramic or spherical image. The capture rate of the camera is user-adjustable by time or distance intervals.