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Digital 3D models of the environment are needed in rescue and
inspection robotics, facility management and architecture. The
problem of automatic environment sensing and modeling is complex,
because a number of fundamental scientific issues are
involved. This paper focusses on how to create a consistent 3D
scene into a common coordinate system from multiple scans. The
proposed algorithms allow to digitize large environments fast and
reliably without any intervention and to solve the simultaneous
localization and mapping (SLAM) problem. Finally, robot motion on
natural outdoor surfaces has to cope with changes in yaw, pitch
and roll angles, turning pose estimation as well as scan matching
or registration into a problem in six mathematical
dimensions. This paper presents a new solution to the SLAM
problem with six degrees of freedom (6D SLAM). A fast variant of
the iterative closest points (ICP) algorithm registers the 3D
scans into a common coordinate system and relocalizes the
robot. Computation time is reduced by two new methods: First, we
reduce the 3D data, i.e., we compute point clouds that
approximate the scanned 3D surface and contain only a small
fraction of that original 3D point cloud. Second, we present a
fast approximation of the corresponding point for the ICP
algorithm. Several approximation methods are evaluated in this
paper. These extensions of ICP result in a fast and robust
algorithm for generating overall consistent 3D maps, using global
error minimization.
In previous work we developed the 6D SLAM algorithm
[20,27]. This paper's main contribution is to
evaluate the approximate data association to speed up the
algorithm. The rest of the paper is organized as follows: Section
II discusses the state of the art in 3D mapping. Then we present
the used 3D laser scanner and the mobile robot. Section IV
describes scan matching and pose estimation, followed by the
application of closest point approximation in the data
association phase. Section VI discusses the results. Section VII
concludes.

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2005-05-03