Algorithm 3 Two-level tracking algorithm.

1:function TRACKING($\mathcal{O}\left\{t\right\}$, $\mathcal{O}\{t-1\}$) 2:    $C_{\left|\mathcal{O}\right\{t\left\}\right|\times \left|\mathcal{O}\right\{t-1\left\}\right|}\leftarrow 0$ 3:    for each object $o\left\{t\right\}\in \mathcal{O}\left\{t\right\}$ do 4:        for each stixel $q\left\{t\right\}\in o$ do 5:           Find correspondence $q\{t-1\}$ for $q\left\{t\right\}$ 6:           Find the object $o\{t-1\}\in \mathcal{O}\{t-1\}$ associated to $q\{t-1\}$ 7:           if $o\{t-1\}$ found and $\parallel o\left\{t\right\}-o\{t-1\}\parallel <{\tau }_{max\_obst\_dist}$ then 8:               $C\left(o\right\{t\},o\{t-1\left\}\right)\leftarrow C\left(o\right\{t\},o\{t-1\left\}\right)+1$ 9:           end if 10:        end for 11:    end for 12:end function