A [[Ray]] is a [[Geometric Primitive]] defined as an infinite line with the start point, alternatively a ray is a [[Line Segment]] with one point at [[Infinity]].
$\huge \R: \vec p = \vec S_{r} + t \hat d $
$\huge \begin{align}
t &\in \R \\
|\hat d| &= 1\\
\end{align} $