Abstract
A two-step method for pose estimation based on five co-planar reference
points is studied. In the first step, the pose of the object is estimated by a
simple analytical solving process. The pixel coordinates of reference points on the
image plane are extracted through image processing. Then, using affine invariants of
the reference points with certain distances between each other, the coordinates of
reference points in the camera coordinate system are solved. In the second step, the
results obtained in the first step are used as initial values of an iterative
solving process for gathering the exact solution. In such a solution, an
unconstrained nonlinear optimization objective function is established through the
objective functions produced by the depth estimation and the co-planarity of the
five reference points to ensure the accuracy and convergence rate of the non-linear
algorithm. The Levenberg-Marquardt optimization method is utilized to refine the
initial values. The coordinates of the reference points in the camera coordinate
system are obtained and transformed into the pose of the object. Experimental
results show that the RMS of the azimuth angle reaches 0.076° in the measurement
range of 0o-90o; the root mean square (RMS) of the pitch angle reaches 0.035o in the
measurement range of 0°-60°; and the RMS of the roll angle reaches
0.036° in the measurement range of 0°-60°.
© 2012 Chinese Optics Letters
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