為了提升無人機的飛行安全，近年來影像處理被置入以提升
飛行導控精準度，光流法為其中一項影像演算法。光流將系統
描述為一種物體運動的圖示，藉由光流可以測量出物體平面運
動之軌跡及速度。本文利用光流法預測相機速度模型，並利用
立體相機提升特徵點擷取精準度，整合加速規、陀螺儀、磁力
計以及氣壓計，將光流規格化轉為向北及向東速度，再與GPS
所測量到的速度比較及分析，利用即時速度回饋解決無人機軌
跡飄移，也可達成室內導航的目的。

In order to raise UAV flight safety, visual processing is introduced to
improve their navigation accuracy in recent years. One of visual processing
algorithm is Optical Flow. Optical Flow is one of the important algorithm
which describes the system as pattern of object’s motion. From the pattern,
object trajectory and horizontal velocity can be measured. The application of
optical flow velocity estimation is proposed in this thesis. In order to improve
optical flow accuracy, stereo camera help optical flow capture feature points
between left and right lens. With integration of accelerometer, gyroscope,
magnetometer and barometer compensation, the optical flow can be
transferred and scaled to North and East velocity. Then analysis and
comparison with NE velocity which measured form GPS, the proposed
optical flow takes the advantage of real-time velocity feedback to solve the
problem of UAV trajectory drifting or can be realize for indoor navigation.

[1] J. J. Zhang, “Precise Velocity and Acceleration Determination Using a Standalone GPS Receiver in Real Time,” Doctor of Philosophy, Mathematical and Geospatial Sciences, RMIT University, 2007.
[2] L. Serrano, D. Kim and R. B. Langley, “A GPS Velocity Sensor: How Accurate Can It Be? – A First Look,” ION NTM, 2004.
[3] J. J. Gibson, “The Perception of the Visual World,” Houghton Miffin Company Boston, 1950.
[4] B. D. Lucas, T. Kanade, “An Iterative Image Registration Technique with an Application to Stereo Vision,” Proceedings of Imaging Understanding Workshop, 1981, pp. 121-130.
[5] B. K. P. Horn and B. G. Rhunck, “Determining Optical Flow,” Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, 1981, pp. 185-203.
[6] D. J. Fleet, Y. Weiss, “Optical Flow Estimation,” In Paragios, Springer, 2006, ISBN 0-387-26371-3.
[7] J. How, N. Pohlman, and C. W. Park, “GPS Estimation Algorithms for Precise Velocity, Slip and Race-track Position Measurements.” SAE Technical Paper, MIT, 2002.
[8] E. Rublee, V. Rabaud, K. Konolige, G. R. Bradski. “ORB: An efficient alternative to SIFT or SURF,” ICCV, 2011, pp. 2564-2571.
[9] E. Rosten, R. Porter and T. Drummond." Faster and Better: A Machine Learning Approach to Corner Detection," in IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 32, No. 1, pp. 105-119, January 2010.
[10] M. Calonder, V. Lepetit and C. Strecha, “BRIEF: binary robust in dependent elementary features,” Berlin Heidelberg: Springer, 2010.
[11] F. K. Noble, “Comparison of OpenCV’s Feature Detectors and Feature Matchers,” International Conference on Mechatronics and Machine Vision in Practice (M2VIP), 2016.
[12] J. Y. Bouguet, “Pyramidal Implementation of the Ane Lucas Kanade Feature Tracker Description of the algorithm,” Intel Corporation, Microprocessor Research Labs, 2000.
[13] J. Weber, J. Malik, “Robust Computation of Optical Flow in a Multi-Scale Differential Framework,” International Journal of Computer Vision, 14, 67-81, 1995.
[14] C. Harris and M. Stephens, “A Combined Corner and Edge Detector.” Proc. 4th Alvey Vision Conf., Manchester, 1988, pp. 147-151.
[15] Mitchell and Tom M, “Machine Learning,” Chapter 3, McGraw-Hill, 1997.
[16] M. Ozuysal, M. Calonder, V. Lepetit and P. Fua, “Fast Keypoint Recognition Using Random Ferns,” IEEE Transactions on Pattern Analysis and Machine Intelligence 32, 2010, pp. 448-461.
[17] R. W. Hamming, "Error detecting and error correcting codes," The Bell System Technical Journal, Vol. 29, No. 2, pp. 147-160, April 1950.
[18] K. H. Dang, D. Le, and T. D. Nguyen, “Efficient determination of disparity map from stereo images with modified sum of absolute differences (SAD) algorithm,” International Conference on Pattern Recognition (ICPR) México, December 4-8, 2016.
[19] M. Shibata, T. Makino and M. Ito, "Target distance measurement based on camera moving direction estimated with optical flow," 10th IEEE International Workshop on Advanced Motion Control, Trento, 2008, pp. 62-67.
[20] G. Cai, B. M. Chen, T. H. Lee, “Unmanned Rotorcraft Systems,” 2011, Chapter 2, Coordinate Systems and Transformations, pp. 23-34.
[21] L. C. Silva, M. R. Petraglia and A. Petraglia, "A robust method for camera calibration and 3-D reconstruction for stereo vision systems," 2004 12th European Signal Processing Conference, Vienna, 2004, pp. 1151-1154.
[22] H. Su and B. He, "A Simple Rectification Method of Stereo Image Pairs with Calibrated Cameras," 2010 2nd International Conference on Information Engineering and Computer Science, Wuhan, 2010, pp. 1-4.
[23] V. Renaudin, M. H. Afzal, and G. Lachapelle, “Complete Triaxis Magnetometer Calibration in the Magnetic Domain,” Journal of Sensors, Volume 1, 2010.
[24] O. H. Sebastian, A. Madgwick, J. L. Harrison, R. Vaidyanathan, “Estimation of IMU and MARG orientation using a gradient descent algorithm,” IEEE International Conference on Rehabilitation Robotics, June 29 - July 1, 2011.
[25] 鄧正隆，慣性技術，Hyweb Technology Co. Ltd., 2011。
[26] S. Madgwick, “An Efficient Orientation Filter for Inertial and Inertial/Magnetic Sensor Arrays,” Report x-io and University of Bristol (UK), 2010.
[27] R. Mahony, T. Hamel, J. M. Pflimlin. “Nonlinear Complementary Filters on the Special Orthogonal Group,” IEEE Transactions on Automatic Control, 53.5, 2008, pp. 1203-1218.
[28] T. Supsukbaworn, C. E. Lin, and H. Y. Chen, “MEMS Implementation in Altitude Stabilization for Unmanned Vertical Take-off/Landing Aircraft. “International Journal of Computer, Consumer and Control (IJ3C), Vol. 4, No.1, 2015, pp. 59-66.
[29] Bowditch and Nathaniel, “American Practical Navigator. Paradise Cay Publications,” 2004, p. 849. ISBN 9780939837540.
[30] J. Bang, D. Lee, Y. Kim and H. Lee, "Camera Pose Estimation Using Optical Flow and ORB Descriptor in SLAM-Based Mobile AR Game," 2017 International Conference on Platform Technology and Service (PlatCon), Busan, 2017, pp. 1-4.
[31] V. Lepetit and P. Fua, “Keypoint Recognition Using Randomized Trees,” IEEE Transactions on Pattern Analysis and Machine Intelligence 28, 2006, pp.1465-1479.
[32] K. Basak, M. Manjunatha and P. K. Dutta, “Pyramidal Refinement of Lucas-Kanade Optical Flow based Tracking of Peripheral Air Embolism in OCT Contrast Imaging,” International Journal of Computer Applications (0975 – 8887) Volume 52-No.12, August 2012.
[33] N. Yadav and C. Bleakley, “Accurate Orientation Estimation Using AHRS under Conditions of Magnetic Distortion,” Sensors, ISSN, 1424-8220, 2014.
[34] M. S. Islam, M. Shajid-Ul-Mahmud, T. Islam, M. S. Amin and M. Hossam-E-Haider, "A low cost MEMS and complementary filter based attitude heading reference system (AHRS) for low speed aircraft," 3rd International Conference on Electrical Engineering and Information Communication Technology (ICEEICT), Dhaka, 2016, pp. 1-5.
[35] S. K. Yang, “Genetic Algorithm Path Planning with Camera Gimbal Tracking for UAV Flight Control,” Master Thesis, Institute of Aeronautics and Astronautics, NCKU, 2014.
[36] Odorid XU4 Datasheet, Hardkernel, Available in May 2017 from website: http://www.hardkernel.com/main/
[37] Tara Stereo Camera Datasheet, E-con Systems, Available in May 2017 from website: https://www.e-consystems.com/
[38] HC06 Datasheet, Guangzhou HC Information Technology, Available in May 2017 from website:
https://www.olimex.com/Products/Components/RF/BLUETOOTH-SERIAL-HC-06/resources/hc06.pdf
[39] Stm32 Datasheet, STMicroelectronics, Available in May 2017 from website: http://www2.st.com/content/st_com/en.html
[40] MPU6500 Datasheet, InvenSence, Available in May 2017 from website: http://www.invensense.com/products/motion-tracking/6-axis/mpu-6500/
[41] HMC5983 Datasheet, Honeywell Microelectronics & Precision Sensors, Available in May 2017 from website:
https://aerocontent.honeywell.com/aero/common/documents/myaerospacecatalog-documents/Defense_Brochures-documents/HMC5983_3_Axis_Compass_IC.pdf
[42] u-blox 6 GPS Datasheet, U-blox, Available in May 2017 from website: https://www.u-blox.com/en
[43] MS5611 Datasheet, TE Connectitivity, Available in May 2017 from website: http://www.te.com/
[44] XBee-PRO S3 Datasheet, DIGI, Available in May 2017 from website: http://www.digi.com/