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Tracking

  Once values which have been estimated during an initialisation step are assigned to the free parameters of a (partially) specialized GOD, we obtain an instance of the vehicle type in question, i. e. an individuum from the class of vehicles indicated by the GOD type. In this case, the instantiated OC will be characterized by its vehicle type - given by the selected specialization of the GOD - and a state vector x which comprises the following components: Since it is assumed that all vehicles move parallel to the road plane which coincides by definition with the ( tex2html_wrap_inline1670 )-plane of the scene coordinate system, the tex2html_wrap_inline1672 -ccordinate of a vehicle will remain constant throughout the tracking process and thus does not need to be represented as a separate component of the OC's state vector.

As may be seen in Figure 4, (a priori) knowledge about the direction of incoming light in the SD can be combined with the knowledge about the hypothesized position and orientation of the OC in order to compute the shadow which the vehicle casts onto the road plane, see [Koller et al. 93].

Standard Computer Graphics techniques including hidden-line-removal are used in order to compute the projection of the instantiated OC into the image plane, again exploiting the knowledge about the position and orientation of the camera viewing the depicted section of the traffic scene. Since it is not assumed that the surface painting of the observed vehicle is known, just the edge segments of the (partially) specialized polyhedral GOD are projected into the image plane, yielding the   Scene Sketch (SS) (see [Kanade 78]) overlayed onto a region cropped from the same image frame as indicated in the bottom panel of Figure 4.




next up previous
Next: Computing Edge Elements (EEs) Up: Outline of the (Edge Previous: Initialisation

HHN (Karlsruhe): Conceptual Descriptions from Image Sequences (Dec. 16, 1996)