This module takes optical flow data as input (that is, a 2D-vector 
movie represented by 2 Fmovies $U$ and $V$) and draw the 2D-vectors defined
on a discrete grid with step $p$. The output is a
Cmovie with a white background and vectors drawn in black as arrows.
Only lines may be drawn by specifying option \verb+-a+. 
A zoom factor may be used with \verb+-z+ option.
Vectors whose norm is below $m$ are not drawn.
The output Cmovie may then be displayed with \verb+cmview+.
\index{optical flow}
