2 Vehicle and Head Geometry
2.1 Vehicle Geometry and Kinematics
       
      The Robot used in this work, shown in Figure 1, has six wheels: four run freely on a fixed transverse axis on each corner, while the two center wheels are motor driven. A high performance four-axis active stereo head (see Figure 2) is mounted with its horizontal tilt axis parallel to the floor, see Figure 4. The fiduciary head center is defined to lie where the pan axis intersects the horizontal plane containing the tilt axis. This point, fixed relative to the vehicle regardless of head movements, is used to define the vehicle’s location relative to a world coordinate frame, as seen in Figure 3.

(a)

(b)
      Figure 1. (a) Photo of the TRC Labmate platform. (b) Robot’s Differential-drive.
       

      The robot is assumed to always move on the xz ground-plane. Its position and orientation are specified by the coordinates (x, z, f). The robot-centered frame has its origin on the ground plane directly under the head center, with its z-axis pointing to the front of the robot, x-axis to the right, and y-axis downwards.


(a)
  


(b)
      Figure 2: (a) TRC Bisight head. (b) Geometry of the active head. P goes vertically through the pan axis and T goes horizontally through the elevation axis.

(a)
  


(b)
      Figure 3. (a) Photo of the robot, showing the mobile platform and the head. (b) The vehicle’s location in the world coordinate frame is specified with the coordinates (x, z, f). The R coordinate frame is carried with the vehicle.

(a)

(b)
      Figure 4. Mobile Platform configuration. (a) Top-view showing the position of the stereo head. (b) Robot’s side-view. All dimensions are in centimeters.
    2.2 Head Geometry

    Locating a feature with the active head provides a 3D measurement of its location from stereo and knowledge of the head geometry (Figure 2(b)). The 3D-position hG of a feature relative to the head center can be calculated in the R vehicle-center frame, if the position uL,vL in the left camera’s image and uR,vR in the right one are known.


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Copyright © 1999 Manuel Noriega.