Center for Mapping
HARDWARE IMPLEMENTATION
The prototype of the integrated GPS/INS/CCD system (Figure 2) designed for precision monitoring of the highway edge- and centerlines comprises two dual-frequency Trimble 4000SSI GPS receivers and a medium-accuracy and high‑reliability strapdown Litton LN-100 inertial navigation system, based on Zero-lockTM Laser Gyro (ZLGTM) and A-4 accelerometer triad (0.8 nmi/h CEP, gyro bias – 0.003°/h, accelerometer bias – 25mg). The LN100 firmware version used in this project allows for access to the raw IMU data, with an update rate up to 256 Hz. Estimation of errors in position, velocity, and attitude, as well as errors in inertial and GPS measurements, is accomplished by a 21-state centralized Kalman filter that processes GPS L1/L2 phase observable in double-differenced mode together with the INS strapdown navigation solution. The estimated standard deviations are at the level of 2-3 cm for position coordinates, and 5-7 arcsec and ~10 arcsec for attitude and heading components, respectively.
The final implementation of the imaging component will be built around the TMC-6700, Pulnix digital camera (Figure 3) or its color version with 9.07mm by 9.16 mm imaging area (9-micron pixel size) and 15 images per second acquisition rate (15 Hz), which allows for 60% overlap in image acquisition at normal highway speed. For testing and performance evaluation of the positioning component, a digital camera based on a 4,096 by 4,096 CCD with 60 by 60 mm imaging area (15 micron pixel size), manufactured by Lockheed Martin Fairchild Semiconductors was used. The imaging sensor of this experimental configuration, (Figure 2), is integrated into a camera-back (BigShot™) of a regular Hasselblad 553 ELX camera body, and the camera is installed on a rigid mount together with the INS.
Figure 1.
Sensor Integration and dataflow block daigram
Figure 2. GPS/INS/CCD hardware configuration
Figure 3. TMC-6700,
Pulnix digital camera