All points and vectors are expressed in homogeneous coordinates. In 2D, points and vectors are represented as [x,y,1]T, and [x,y,0]T, respectively. 3D points and vectors may be represented with an extra depth (z) component, or with a disparity component; 3D transformations must be computed accordingly. For disparity maps, a rigid object motion can be simulated with a rigid camera motion (see Appendix B). The presentation in the remainder of this paper applies equally to 2D (planar) or 3D transformations.
We represent the appearance of a body segment as a
matrix called an image list:
![$A=\mbox{$\left [ \begin{array}
{c} {S} \\ {X}\end{array} \right ]$}=\left [ \b...
...ay}
{cccc} p_1 & p_2 &
p_3 & ... \\ t_1 & t_2 & t_3 & ... \end{array} \right ]$](img2.gif)
, where each
ti=[ri,gi,bi]T contains texture information. This
representation is similar to a layered depth image [22], but
is more convenient for expressing point correspondences. (Layered
depth images allow efficient incremental computation during reprojection.)