Hi,
Try this! Can be a starting for you.
Code:
(defun c:relative_angle ( / js oldsnap oldortho dxf_ent alpha ang_supp)
(princ "\nSelection of reference line.")
(setq js (ssget "_+.:E:S" '((0 . "LINE"))))
(cond
(js
(setq
oldsnap (getvar "snapang")
oldortho (getvar "orthomode")
dxf_ent (entget (ssname js 0))
alpha (angle (trans (cdr (assoc 10 dxf_ent)) 0 1) (trans (cdr (assoc 11 dxf_ent)) 0 1))
)
(initget 1)
(setq ang_supp (getangle "\nAngle to add: "))
(setvar "snapang" (+ alpha ang_supp))
(setvar "orthomode" 1)
(command "_.line" pause "_none" pause "")
(setvar "orthomode" oldortho)
(setvar "snapang" oldsnap)
(command "_.line" "")
)
)
(princ)
)