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IMPROVING TRACKING TRAJECTORIES WITH MOTION
ESTIMATION
J. Pomares, G. J. García, F. Torres
Physics, Systems Engineering and Signal Theory Department. University of Alicante, Alicante, Spain
Keywords: Motion estimation, tracking trajectories, visual control.
Abstract: Up to now, different methods have been proposed to track trajectories using visual servoing systems.
However, when these approaches are employed to track trajectories specified with respect to moving
objects, different considerations must be included in the visual servoing formulation to progressively
decrease the tracking error. This paper shows the main properties of a non-time dependent visual servoing
system to track image trajectories. The control action obtained integrates the motion estimation of the object
from which the features are extracted. The proposed motion estimator employs information from the
measures of the extracted features and from the variation of the camera locations. These variations are
obtained determining the Homography matrix between consecutive camera frames.
1 INTRODUCTION
Now, visual servoing systems are a well-known
approach to guide a robot using image information.
Tipically, visual servoing systems are position-based
and image-based classified (Hutchinson et al. 1996).
Position-based visual servoing requires the
computation of a 3-D Cartesian error for which a
perfect CAD-model of the object and a calibrated
camera are necessary. These types of systems are
very sensitive to modeling errors and noise
perturbations. In image-based visual servoing the
error is directly measured in the image. This
approach ensures the robustness with respect to
modeling errors, but generally an inadequate
movement of the camera in the 3-D Cartesian space
is obtained. On the other hand, it is well known that
image-based visual servoing is locally stable. This
nice property ensures a correct convergence if the
desired configuration is sufficiently near to the
current one. This paper shows the properties of an
approach which employs image-based visual
servoing to track trajectories. This method is not the
main objective of the paper and a more extensive
study of the approach can be seen in our previous
works (Pomares and Torres, 2005).
Once this strategy is defined, the paper focuses on
the extension of the previous mentioned algorithms
to be able to carry out the tracking of image
trajectories when the visual features are in motion.
Previous works, such as (Hutchinson et al. 1996)
have shown the necessity of estimating object
motion and to include this estimation in the control
action in order to decrease the tracking errors. The
motion estimation can be solved using different
algorithms like the one shown in (Pressigout and
Marchand, 2004) based in virtual visual servoing. In
(Bensalah and Chaumette, 1995) an estimator which
employs measurements about the camera velocity is
proposed. However, this method introduces errors in
the estimation due to the non accuracy measurement
of the camera motion. The previous mentioned
algorithms are used to achieve a given configuration
of the features in the image. In this paper, we define
method to improve the estimation of the camera
velocity based on visual information. This method is
used to define a motion estimator to be applied
during the tracking of trajectories.
This paper is organized as follows: The main
aspects of the visual servoing system to track
trajectories are first described in Section 2. Section 3
shows a method to estimate the motion of the object
from which the features are extracted. Section 4,
simulation and experimental results confirm the
validity of the proposed algorithms. The final
section presents the main conclusions arrived at.
97
Pomares J., J. García G. and Torres F. (2006).
IMPROVING TRACKING TRAJECTORIES WITH MOTION ESTIMATION.
In Proceedings of the Third International Conference on Informatics in Control, Automation and Robotics, pages 97-103
DOI: 10.5220/0001212400970103
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SciTePress