## vlax routine perpendicular lines along polyline.

I am working on this routine to draw perpendicular along a polyline. This routine will be creating some 3d geometry based on a couple of 3D pick points. The problem I haven't figured out just yet is how do I calculate the perpendicular angle at a specified distance along the polyline.

I have attached the code that will place a POINT entity at the selected places. The inserted point will be replaced with some code to draw the necessary 3d geometry. I already have the 3d geometry code written. I just need to calculate the perpendicular angle of the polyline. The polyline will most likely contain some kind of arc and possible more than one arc and a tangent.

Code:
```(defun C:TEST ()
(setq	ENTITY	    (entget (car (entsel "\nSelect alignment: ")))
VLAX-ENTITY (vlax-ename->vla-object (cdr (assoc -1 ENTITY)))
VLAX-LENGTH (if	(vlax-property-available-p VLAX-ENTITY 'length)
(vlax-get-property VLAX-ENTITY 'length)
)
)
(setq OSM (getvar "osmode"))
(if VLAX-LENGTH
(progn
(setq INCREMENT (fix (/ VLAX-LENGTH 3.0)) ;_ Arbetrary length of 3.0 for testing.
INCREMENT (/ VLAX-LENGTH INCREMENT)
)
(setvar "osmode" 0)
(repeat (- (fix (/ VLAX-LENGTH 3.0)) 1)
(setq VLAX-LENGTH (- VLAX-LENGTH INCREMENT))
(setq TempPoint (vlax-curve-getpointatdist VLAX-ENTITY VLAX-LENGTH))
(command "_.point" TempPoint)
; This is the place in the code I need to calculate
; the perpendicular angle of the polyline.  As you can
; see this angle will change based on where along the
; polyline the point is located.
)
)
)
(vlax-release-object VLAX-ENTITY)
(setvar "osmode" OSM)
)```