Global Positioning System Reference
In-Depth Information
Table 3. Accuracy of the image orientation
4.3 Hybrid positioning by multi sensor integration
The position and attitude of the sensors are dictated by the integration of the GPS and IMU
data, as well as by the image orientations that are acquired from digital cameras or digital
video cameras. One of the main objectives of this paper is to integrate inexpensive sensors
into a high-precision positioning system. Integration of the GPS (which operates at 1 Hz)
with the IMU (200 Hz) has to be made with Kalman filtering for the geo-referencing of laser
range data with a frequency of 18 Hz. The positioning accuracy of the GPS/IMU integration
data is based on GPS accuracy. On the other hand, both position and attitude can be
estimated with very high accuracy using the BBA as image orientations. However, the
images are not taken frequently; in this case every 10 seconds.
Therefore, the combination of the BBA and Kalman filtering is conducted to increase
accuracy, as shown in Figure 6. The BBA results are assumed to be true position values.
They provide initial attitude and heading without any IMU alignment. The IMU is
initialized by Kalman filtering using the BBA result every 10 seconds to avoid a culmination
of errors. That is, after every computation of the BBA, the IMU data and its errors are
corrected. Figure 6 shows the strapdown navigation algorithm for the GPS/IMU integration
and the BBA result. The combination of GPS, IMU, and images can be a hybrid positioning.
As a result of the multi sensor integration, the trajectory of the hybrid positioning can assure
sufficient geo-referencing accuracy for the images. The trajectory of the digital camera can
be representative of the trajectory of the platform because the GPS and IMU data are
initialized by camera orientation. Their coordinate is fitted to the digital camera coordinate.
Figure 7 shows the hybrid position as trajectories of GPS/IMU/images and GPS/IMU. The
coordinate system is JGD2000 (Japan Geodetic Datum 2000). The black solid line is the
combination of GPS/IMU/images, and the red solid line is the ordinary combination of
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