Too bad, you cannot see the grid on the picture I sent before. The lines 
are starting at the center of the cells and the dot is at the end of the 
line pointing into the direction. I attached another picture with 
different sized vectors and a visible grid.

A T would probably be faster. I have tried a rectangle instead of the 
dot before, but this looked rather confusing.

On 01.10.2015 18:20, Sean Luke wrote:
> Do you think the dot should be at the center of the cell?  That is, a
> maximum-length line would be half the width of the cell?  Or should
> the center of the cell be the center of the line?
> If speed is at issue, a small orthogonal line, like a T, would be a
> bit faster than a dot; might do that.
> Sean
> I also note from below that your class is basically a replacement for
> OrientedPortrayal2D: it can be used (and from the picture, appears to
> be used) in ContinuousPortrayal2D, for example.