Get z value from 2d Point which is exact on 3D polyline

[Anonymous]

I have 2D point which is  exact on 3D polyline. get z value of that  Point which is on 3D Polyline.

[dbhunia]

You can approach like this....

(defun C:get_z_val ( / sp l PC PI)
        (princ "Select the Point...")
	(setq SP (ssget "_:S" '((0 . "POINT"))))
	(setq L (vlax-ename->vla-object (car (entsel "\nSelect the line: "))))
	(setq PC (cdr (assoc 10 (entget (setq EP (ssname SP 0))))))
	(command "_.xline" "_none" PC "_none" (list (car pc) (cadr pc) 100) "")
	(setq PI (vlax-invoke (vlax-ename->vla-object (entlast)) 'IntersectWith L acExtendNone))
	(entdel (entlast))
	(if PI (princ (strcat "\nZ value of the Point on Line: " (rtos (caddr PI) 2 1)))
		   (princ "\nLine is not exactly on the picked point....")
	)
	(princ)
)

[john.uhden · Accepted solution]

If p0 is your 2D point exactly under/over a 3DPolyline, and the 3DPoly is a vla-object, then...

(setq p (vlax-curve-getclosestpointtoprojection object p0 '(0 0 1)))

which will include the desired Z value.

Actually, it doesn't have to be a 3DPoly; it could be a line or any other curve-type object.

[g_dossier]

I saw this post and thought its exactly what i need, I have a series of coordinates in exact distance say 0.5m, the coordinates has a z=0, and along that coordinates if you plot it in CAD theres a 3d strings above it, I would like to get that z value at exactly the same point to that 2d coordinates. Would you mind help with this?