projecting to a surface - relative->absolute elevations

I would like to ask for your help for the following case.

I generated a surface from points with absolute coordinates (X, Y, Z).

I have got some lines representing underground utilities. X,Y coordinates match with the surface, but unfortunately the elevations are relative (from 0 to -1.5). Is there any tricky method to project these lines to the surface, and keep the point's relative distance from it?

Thanks,

TRicKolas

Your profile says LT so no easy way, in CIV3D can lay a point on a surface then you could move it verticaly. If you have 3dfaces in LT then you could possibly do it, a bit long winded method using trim which hopefully in LT works the same that you can trim a 3d line.

I should have updated my profile, sorry for missing that.

We have a subscription to Civil, as well. I use aeccfeatureelevsfromsurf command to project the lines to the surface itself, but my knowledge ends here. After that I have to lower to 3dpoly vertix by vertix, which is not an effective way to do this.

A couple of ways make sure intermittent Grade breaks is off. For a single line make it a pline add to surface then explode and you can get to Z in properties but cumbersome. But using a lisp can change the Z value.

(while (setq tp1 (entsel "\nSelect left side inner wall near end : "))
 (setq tpp1 (entget (car tp1)))
 (setq pt1 (cdr (assoc 10 tpp1)))      
 (setq pt2 (cdr (assoc 11 tpp1)))      
 (setq pt3 (cadr tp1))
 (setq d1 (distance pt1 pt3))
 (setq d2 (distance pt2 pt3))
   (if (> d1 d2)
   (progn 
     (setq temp pt1)
     (setq pt1 pt2)
     (setq pt2 temp)
   )
   )
(setq Z (+ (caddr pt1) (getreal "Enter difference")))
(setq xyz (list (car pt1)(cadr pt1) z))
(entmod (subst (cons 10 xyz) (assoc 10 tpp1) tpp1))
)