\setlength{\abovedisplayskip}{2pt}
\begin{align*}
C\left( {x,\xi ,\theta ,r} \right): = \{ x + ty:y \in {R^d},{\left\| y \right\|_2} = 1,{y^T}\xi  \ge \cos \theta ,t \in \left[ {\circ,r} \right]\}
\end{align*}
\setlength{\belowdisplayskip}{2pt}