\filldraw  (B) circle (1pt) node [anchor=north] {$B$};
\draw [thick] ($(B)!\sb!(Q)$) -- (Q);
\draw [thick,dotted] (Q) -- ($(B)!2.3!(Q)$);
\draw ($(B)!\sa-0.4!(Q)$) node {$t$};

%Must be last
\filldraw [color=white] (Q) circle (2pt) ;
\draw  (Q) circle (2pt) node [above] {?};
