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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
Attitude 
Figure 8. Attitude estimation from the Gyro measurements 
Figure 7 plots the velocities in three directions estimated by the 
vision based subsystem comparing with the DGPS measured 
velocity, while Figure 8 show the attitude results from the gyro 
measurements directly. The velocity estimated by the vision 
based subsystem follow closely to the GPS measurements. 
Optical flow and LRF error states 
Figure 9. KF2 error states 
The four states of KF2 are plotted in Figure 9, which show a 
relatively quick convergence. The estimated errors are 
consistent with the specifications of the corresponding sensors. 
5.2 Integrated navigation with GPS outage 
Simulated GPS outage (90 seconds) is applied to the integrated 
system. Figure 10 shows the positioning results, and velocity 
results are depicted in Figure 11. The measurements from the 
LRF, optic flow and gyros are processed to obtain the vision 
based navigation solutions, which are very sable over time 
without GPS aiding. 
6. CONCLUDING REMARKS 
The two independent Kalman filtering designs for all the 
sensors onboard the UAV have significant advantages as there 
are redundant navigation solutions to guarantee the reliability of 
the navigation operations. The experiment results have 
demonstrated the feasibility of using optic flow height control 
for a rotorcraft automatic control and landing. The results of 
preliminary investigations are encouraging and this method can 
be further developed with the inclusion of error modelling and 
estimation for gyro biases, etc. 
Positioning: NED 
Figure 10. Horizontal positioning with GPS outage 
Figure 11. Velocity estimation with GPS outage 
REFERENCES 
Brown, R.G. and Hwang, P.Y.C., 1997. Introduction to Random 
Signals and Applied Kalman Filtering. John Wiley & Sons Inc., 
New York. 
Chatteiji, G.B., Menon, P.K. and Sridhar, B., 1997. 
GPS/Machine Vision Navigation System for Aircraft. IEEE 
Transactions on Aerospace and Electronic System, 33(3): 1012- 
1024. 
Dissanayake, M.W.M.G., Newman, P., Durrant-Whyte, H., 
Clark, S. and Csorba, M., 2001. A solution to the simultaneous 
localization and map building problem. IEEE Transactions on 
Robotics and Automation, 17(3): 229-241.