topic Re: normal intersection in Visual LISP, AutoLISP and General Customization Forum

normal intersection

scott_bolton — Thu, 09 Oct 2025 12:27:29 GMT

I'd like to find the intersection of a normal FROM a reference line and not TO a secondary line. (vlax-curve-getClosestPointTo ent2 pt) returns the normal to obj2 from pt (grey in the attached image), but I want the red coordinate.
I could offset a line from ent1 then use (vlax-curve-getClosestPointTo ent3 pt) to create the dashed red line then use (vla-IntersectWith ent2 ent4) but if there's a quicker method I'd rather use that.

Re: normal intersection

ВeekeeCZ — Thu, 09 Oct 2025 12:54:28 GMT

Both are actual LINEs? If so, use (inters) func.

Re: normal intersection

daniel_cadext — Thu, 09 Oct 2025 13:27:16 GMT

I think Lee Mac might have some helpers for vectors, Assuming the lines are planar, you will want to:

- find the direction of the line as a vector, or angle so you can use polar point

- create a ray or xline perpendicular to the line

- find the intersection of the ray/xline with your target line

proof of concept

from pyrx import Db, Ed, Ge, Ap, Rx, Gs @Ap.Command() def doit(): try: ps1, id1, pnt1 = Ed.Editor.entSel("\nSelect 1: ", Db.Curve.desc()) ps2, id2, pnt2 = Ed.Editor.entSel("\nSelect 2: ", Db.Curve.desc()) c1 = Db.Curve(id1) c2 = Db.Curve(id2) dir1 = c1.getPointAtParam(0) - c1.getPointAtParam(c1.getEndParam()) geline = Ge.Line3d(pnt1, dir1.perpVector()) gec2 = c2.getAcGeCurve() if not gec2.isKindOf(Ge.EntityId.kLinearEnt3d): raise RuntimeError("oof not a kLinearEnt3d") flag, inters = geline.intersectWith(Ge.LinearEnt3d.cast(gec2)) if flag: Ed.Core.grDraw(pnt1, inters, 1, 0) except Exception as err: print(err)

Re: normal intersection

komondormrex — Thu, 09 Oct 2025 13:47:30 GMT

try this one

(setq this_point (vlax-curve-getclosestpointtoprojection (car (entsel "\nPick ent2: ")) (getpoint "\nPick point pt: ") '(0 1 0)))

Re: normal intersection

pkenewell6347 — Thu, 09 Oct 2025 13:59:53 GMT

If you are in 2D - here's the basic code example to do what you want for lines or polylines:

(defun c:foo (/ a e1 e2 et1 et2 ep1 ep2 g1 g2 n1 p1 p2 pp o1 o2 sp1 sp2) (if (and (setq g1 (entsel "\nSelect first line: ")) (setq g2 (entsel "\nSelect second line: ")) ) (progn (setq p1 (cadr g1) p2 (cadr g2) e1 (car g1) e2 (car g2) et1 (cdr (assoc 0 (entget e1))) et2 (cdr (assoc 0 (entget e2))) o1 (vlax-ename->vla-object e1) o2 (vlax-ename->vla-object e2) p1 (vlax-curve-getclosestpointto o1 p1) p2 (vlax-curve-getclosestpointto o2 p2) ) (cond ((= et1 "LINE") (setq sp1 (vlax-curve-Getstartpoint o1) ep1 (vlax-curve-Getendpoint o1) ) ) ((= et1 "LWPOLYLINE") (setq pp (vlax-curve-getparamatpoint o1 p1) sp1 (vlax-curve-getpointatparam o1 (fix pp)) ep1 (vlax-curve-getpointatparam o1 (1+ (fix pp))) ) ) ) (setq a1 (angle sp1 ep1) n1 (polar p1 (+ a1 (/ pi 2)) 1) ) (cond ((= et2 "LINE") (setq sp2 (vlax-curve-Getstartpoint o2) ep2 (vlax-curve-Getendpoint o2) ) ) ((= et2 "LWPOLYLINE") (setq pp (vlax-curve-getparamatpoint o2 p2) sp2 (vlax-curve-getpointatparam o2 (fix pp)) ep2 (vlax-curve-getpointatparam o2 (1+ (fix pp))) ) ) ) (if (setq p3 (inters p1 n1 sp2 ep2 nil)) (command "._line" "_non" p1 "_non" p3) ) ) ) )

Re: normal intersection

leeminardi — Thu, 09 Oct 2025 15:22:16 GMT

The following will work in 3D but assumes that the two line lie in the same plane.

(defun c:project2line ( / line1 line2 ent1 ent2 normal pt p1 p2 p3 p4 p5 p6 ) ; projects a point from line 1 to line 2 (vl-load-com) ; Load Visual LISP extensions ; Prompt user to select the first line (setq line1 (entsel "\nSelect the first line: ")) (if line1 (progn (setq ent1 (car line1)) (if (= (cdr (assoc 0 (entget ent1))) "LINE") ; Check if it's a LINE entity (progn (setq obj1 (vlax-ename->vla-object ent1)) ; Convert entity name to VLA-object (setq p1 (vlax-safearray->list (vlax-variant-value (vla-get-startpoint obj1)))) (setq p2 (vlax-safearray->list (vlax-variant-value (vla-get-endpoint obj1)))) ) (princ "\nSelected entity is not a line.") ) ) (princ "\nNo first line selected.") ) (setq line2 (entsel "\nSelect the second line: ")) (if line2 (progn (setq ent2 (car line2)) (if (= (cdr (assoc 0 (entget ent2))) "LINE") ; Check if it's a LINE entity (progn (setq obj2 (vlax-ename->vla-object ent2)) ; Convert entity name to VLA-object (setq p3 (vlax-safearray->list (vlax-variant-value (vla-get-startpoint obj2)))) (setq p4 (vlax-safearray->list (vlax-variant-value (vla-get-endpoint obj2)))) ) (princ "\nSelected entity is not a line.") ) ) (princ "\nNo second line selected.") ) (setq pt (getpoint "\nIdentify point on LINE 1 to project to LINE 2. ")) (setq normal (cross (mapcar '- p2 pt) (mapcar '- pt p3))) (setq p5 (mapcar '+ pt (cross normal (mapcar '- p2 pt)))) (setq p6 (inters p3 p4 pt p5 nil)) ;(command "_point" "_non" p6) (command "_line" "_non" pt "_non" p6 "") (princ) ) ;;; Compute the cross product of vectors a and b (defun cross (a b / crs) (setq crs (list (- (* (nth 1 a) (nth 2 b)) (* (nth 1 b) (nth 2 a)) ) (- (* (nth 0 b) (nth 2 a)) (* (nth 0 a) (nth 2 b)) ) (- (* (nth 0 a) (nth 1 b)) (* (nth 0 b) (nth 1 a)) ) ) ;end list ) ;end setq c ) ;end cross

[Code edited 10/9/2025 to add line instead of point and change program name]

Re: normal intersection

devitg — Thu, 09 Oct 2025 15:02:40 GMT

Please try it

(defun c:vert-line (/ AUX-LINE G2 PT1 PT@G2 PTAUX XYZ@G2 ) (setq pt1 (cadr (entsel "\nSelect Point at first line: "))) (setq g2 (entsel "\nSelect second line: ")) (setq ptaux (polar pt1 (* 0.5 pi) 10)) (command "_line" pt1 ptaux "") (setq aux-line (entlast)) (setq pt@g2 (VLA-INTERSECTWITH (VLAX-ENAME->VLA-OBJECT aux-line) (VLAX-ENAME->VLA-OBJECT (car g2)) 1 ) ;_ end of VLA-INTERSECTWITH ) ;_ end of setq (Setq xyz@g2 (VLAX-SAFEARRAY->LIST (VLAX-VARIANT-VALUE pt@g2))) (command "line" pt1 xyz@g2 "") (command "erase" aux-line "") ) ;_ end of defun

Re: normal intersection

scott_bolton — Thu, 09 Oct 2025 18:03:54 GMT

They could be LINEs or LWPOLYLINEs with arc elements so inters won't work, and this is where a couple of the ones below fail.

Re: normal intersection

scott_bolton — Thu, 09 Oct 2025 18:04:39 GMT

This isn't LISP so is beyond me; I'm not able to see if it works or not.

Re: normal intersection

scott_bolton — Thu, 09 Oct 2025 18:06:09 GMT

This works for straight LINEs or LWPOLYLINEs but not if the LWP contains arcs.

Re: normal intersection

scott_bolton — Thu, 09 Oct 2025 18:06:44 GMT

This works for straight LINEs or LWPOLYLINEs but not if the LWP contains arcs.

Re: normal intersection

scott_bolton — Thu, 09 Oct 2025 18:08:13 GMT

I haven't checked this because I notice it creates a temporary LINE which I was hoping to avoid. However, it looks like this is the (only) way to do it.

Re: normal intersection

Kent1Cooper — Fri, 10 Oct 2025 12:22:49 GMT

If a temporary Line is to be drawn anyway, you could try my (pf) [= perpendicular from] function, >here<. See the description at Message 6 of that topic, but don't use the code there -- use the code attached at the linked Message.

It works to draw something like a Line [or as a Move or Copy displacement, or...] perpendicular from anything with linearity -- Line, Polyline [including arc segments], Circle, Arc, Ellipse, Spline, Ray, or Xline. If you use it to draw a Line, just draw it past the other object, and take the intersection.

Re: normal intersection

pkenewell6347 — Thu, 09 Oct 2025 18:48:17 GMT

FWIW: Here's a new version of my code that uses a temp line and (vla-intersectwith):

(defun c:foo (/ a doc e1 e2 et1 ep1 g1 g2 n1 p1 p2 p3 pp o1 o2 sp1 spc) (vl-load-com) (setq doc (vla-get-activedocument (vlax-get-acad-object)) spc (if (> (getvar "CVPORT") 1)(vla-get-modelspace doc)(vla-get-paperspace doc)) ) (if (and (setq g1 (entsel "\nSelect first line: ")) (setq g2 (entsel "\nSelect second line: ")) ) (progn (setq p1 (cadr g1) p2 (cadr g2) e1 (car g1) e2 (car g2) et1 (cdr (assoc 0 (entget e1))) o1 (vlax-ename->vla-object e1) o2 (vlax-ename->vla-object e2) p1 (vlax-curve-getclosestpointto o1 p1) ) (cond ((= et1 "LINE") (setq sp1 (vlax-curve-Getstartpoint o1) ep1 (vlax-curve-Getendpoint o1) ) ) ((= et1 "LWPOLYLINE") (setq pp (vlax-curve-getparamatpoint o1 p1) sp1 (vlax-curve-getpointatparam o1 (fix pp)) ep1 (vlax-curve-getpointatparam o1 (1+ (fix pp))) ) ) ) (setq a1 (angle sp1 ep1) n1 (polar p1 (+ a1 (/ pi 2)) 1) o3 (vla-addline spc (vlax-3d-point p1) (vlax-3d-point n1)) ) (if (setq p3 (vlax-safearray->list (vlax-variant-value (vla-intersectwith o3 o2 acExtendBoth)))) (vla-addline spc (vlax-3d-point p1) (vlax-3d-point p3)) ) (vla-delete o3) ) ) )

Re: normal intersection

calderg1000 — Thu, 09 Oct 2025 19:17:55 GMT

Try this code...

(defun c:Int(/) (command "_point" "_non" (vlax-curve-getClosestPointToProjection (car (entsel "\nSelect Object 2")) (getpoint "\nPick Point: ") '(0 -1 0) t ) ) )

Re: normal intersection

Moshe-A — Thu, 09 Oct 2025 19:28:53 GMT

@scott_bolton hi,

here is my simple version , without the need of temporary line 😀

(MA:ginters ....) function, accepts 5 arguments, the first 4 represent the 4 points of the selected segments and the last is the picked reference point.

the geometric idea is to create a right angled (90) triangle on the first selected line (base) with one of the points on the second selected line, finding the direction of the face edge [ using (cos) function ] from the second point putting this vector on the picked reference point.

the (c:xxx) command is to show how to use the function - supports lines or\and pline segment.

enjoy

Moshe

;;; MA:ginters ;;; OCT 09, 2025 by Moshe-A ;;; Argumenst ;;; t0 - first pt of first vector ;;; t1 - second pt of first vector ;;; t2 - first pt of second vector ;;; rpt - reference\picked point on first vector (defun MA:ginters (t0 t1 t2 t3 rpt / right_angle ; local function ang2 ang3 ax bx cx t4 t5) ; local variables ; triangle right angle (defun right_angle (/ a0 a1 a2) (setq a0 (angle t0 t1)) (setq a1 (angle t0 t2)) (if (> a1 a0) (setq a2 (- a1 a0)) (setq a2 (- a0 a1)) ) (if (> a2 (* pi 1.5)) (- (* pi 2) a2) a2 ); if ); right_angle ; here start ginters (setq ang2 (right_angle)) ; triangle right angle (setq cx (distance t0 t2)) ; triangle hypotenuse (setq bx (* cx (cos ang2))) ; near edge length (setq t4 (polar p0 (angle t0 t1) bx)) (setq ax (distance t4 t2)) ; face edge length (setq ang3 (angle t4 t2)) ; face edge angle from t4 (setq t5 (polar rpt ang3 ax)) ; paralle vector from rpt (inters t2 t3 rpt t5 nil) ; return intersection ); MA:ginters (vl-load-com) ; load avtivex support (defun c:xxx (/ getVector ; local function pick0 pick1 ename0 ename1 ptx0 ptx1) ; p0 p1 p2 p3 ptr PTM cr) ; ent - ename of selected object ; ppt - picked point (defun getVector (ent ppt Qt0 Qt1 / elist prm) (setq elist (entget ent)) (cond ((eq (cdr (assoc '0 elist)) "LINE") (set Qt0 (vlax-curve-getStartPoint ent)) ; indirect set (set Qt1 (vlax-curve-getEndPoint ent)) ; indirect set ); case ((eq (cdr (assoc '0 elist)) "LWPOLYLINE") (setq prm (vlax-curve-getParamAtPoint ent ppt)) (set Qt0 (vlax-curve-getPointAtParam ent (fix prm))) ; indirect set (set Qt1 (vlax-curve-getPointAtParam ent (1+ (fix prm)))) ; indirect set ); case ( t (vlr-beep-reaction) (prompt "\n* Require line or pline *") ) ); cond ); getVector ; here start c:xxx (if (and (setq pick0 (entsel "\nPick first line: ")) (setq ename0 (car pick0)) (setq ptx0 (vlax-curve-getClosestPointToProjection ename0 (cadr pick0) '(0.0 0.0 1.0))) (getVector ename0 ptx0 'p0 'p1) (setq pick1 (entsel "\nPick second line: ")) (setq ename1 (car pick1)) (setq ptx1 (vlax-curve-getClosestPointToProjection ename1 (cadr pick1) '(0.0 0.0 1.0))) (getVector ename1 ptx1 'p2 'p3) (setq ptr (getpoint "\nSpecify reference point on first line: ")) (setq PTM (osnap ptr "_Nearest")) ) (if (not (equal (+ (distance p0 PTM) (distance PTM p1)) (distance p0 p1) 1e-4)) (progn (vlr-beep-reaction) (prompt "\n* Reference point is not found on first line *") ); progn ; else (if (setq cr (MA:ginters p0 p1 p2 p3 PTM)) (command ".line" PTM cr "") ) ); if ); if (princ) ); c:xxx

Re: normal intersection

pkenewell6347 — Thu, 09 Oct 2025 19:42:06 GMT

This will only get the projected point if the first line is horizontal. However - I see where you are thinking. you just have to get the normal correctly from the first line segment.

Re: normal intersection

pkenewell6347 — Thu, 09 Oct 2025 20:52:39 GMT

Based on @calderg1000 idea, This does not use a temporary line:

EDIT: Updated to ignore if there is not an intersect at the normal.

(defun c:foo (/ _getunitvect a e1 e2 et1 ep1 g1 g2 n1 p1 p2 p3 pp o1 o2 sp1) (defun _getunitvect (p1 p2 / v) (setq v (mapcar '- p1 p2)) ( (lambda (l)(if (/= 0 l) (mapcar (function (lambda (x) (/ x l))) v))) (distance '(0 0 0) v) ) ) (vl-load-com) (if (and (setq g1 (entsel "\nSelect first line: ")) (setq g2 (entsel "\nSelect second line: ")) ) (progn (setq p1 (cadr g1) e1 (car g1) e2 (car g2) et1 (cdr (assoc 0 (entget e1))) o1 (vlax-ename->vla-object e1) o2 (vlax-ename->vla-object e2) p1 (vlax-curve-getclosestpointto o1 p1) ) (cond ((= et1 "LINE") (setq sp1 (vlax-curve-Getstartpoint o1) ep1 (vlax-curve-Getendpoint o1) ) ) ((= et1 "LWPOLYLINE") (setq pp (vlax-curve-getparamatpoint o1 p1) sp1 (vlax-curve-getpointatparam o1 (fix pp)) ep1 (vlax-curve-getpointatparam o1 (1+ (fix pp))) ) ) ) (setq a1 (angle sp1 ep1) n1 (_getunitvect p1 (polar p1 (- a1 (/ pi 2)) 1)) ) (if (and (setq p2 (vlax-curve-getClosestPointToProjection o2 p1 n1 T)) (equal n1 (_getunitvect p1 p2) 0.0001 ) ) (command "._line" "non" p1 "_non" p2 "") ) ) ) )

Re: normal intersection

ВeekeeCZ — Thu, 09 Oct 2025 20:46:33 GMT

Projection...

(defun c:foo nil
  
  (setq e1 (Car (entsel "1: ")))
  (setq e2 (car (entsel "2: ")))
  (setq p (getpoint "point on 1: "))
  
  (setq d (vlax-curve-getfirstderiv e1 (vlax-curve-getparamatpoint e1 p)))
  (setq n (list (- (cadr d)) (car d) 0))
  
  (command "_point" "_non" (vlax-curve-getclosestpointtoprojection e2 p n t))
  
  )

Re: normal intersection

pkenewell6347 — Thu, 09 Oct 2025 21:19:18 GMT

That works, However - I've noticed that (vlax-curve-getclosestpointtoprojection) still returns a value even if the projection does not intersect (usually the start or end of the curve). Have to figure out a way to compare the normals and ignore if the the curve does not actually intersect.

I admit - I'm not good with how derivatives work.