Well, at point P, the velocity vector QP is perpendicular to the line QP, 1 so the sine of that angle is one.

点P，速度向量,垂直于直线，所以该角的正弦值为。

youdao

For the case of planar interception, the so called relative heading error angle between the relative velocity vector and the LoS (Line of Sight) is chosen as the output to be controlled to zero.

针对平面拦截问题，选择导弹和目标之间的相对速度矢量与导弹-目标视线之间的夹角（称为相对航向误差角）作为将要被控制到零的输出。

youdao