(setq sta1 (getreal "\n輸入起始樁號<0K+???>:"))
(if (null sta1) (setq sta1 30.))
(setq Prm (vlax-curve-getParamAtDist enx sta1))
(setq Pt (vlax-curve-getPointAtParam enx Prm))
(setq Dri (vlax-curve-getFirstDeriv enx Prm))
(setq Ang (+ (* pi 0.5) (angle '(0 0 0) Dri)))
上列四個式子分別代表什麼意思啊