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I'm interested in where this topic will be going with the different "side quests" like islands and inlets. In the mean time I kept going, trying to fix my version and after a lot of testing/debugging I changed to code again. Now it is working as expected on all of the examples I have found! ;| ; Calculate centerline between two polylines - dexus ; Function checks intersections of the offsets of two lines to create a middle/avarage line. ; https://www.cadtutor.net/forum/topic/98778-hybrid-parallel/page/7/#findComment-677877 ; Version / Date - Change ; 0.01 [19-11-2025] - Initial release ; 0.02 [27-11-2025] - Added corner support on negative side of crossing polylines ; 0.03 [28-11-2025] - Extra check using vertex to closest point as distance ; 0.04 [28-11-2025] - Added error function ; 0.05 [01-12-2025] - Improved distance check to prevent zigzag lines ; 0.06 [01-12-2025] - Check if offset can be used before adding points ; 0.07 [01-12-2025] - Improved side check on 3 points ; 0.08 [04-12-2025] - Don't compare startpoint to offset when eiter of the polylines is closed ; 0.09 [05-12-2025] - Add points for parallel end segments ; 0.10 [18-12-2025] - More checks for deleting lines and added dedicated function ; 0.11 [08-01-2026] - Support for multiple output lines of the offset function ; 0.12 [08-01-2026] - Bulges are transformed to lines to handle cocentric arcs ; 0.13 [08-01-2026] - Rewrote the _avarageAngle and _diffAngle function |; (defun c:cl (/ corners ent1 ent2 gap index loop maxlen offset offsetdistance org1 org2 parallel pts sides ss start te0 te1 te2 tmp1 tmp2 LM:ProjectPointToLine LM:intersections _addPoints _avarageAngle _checkOffset _checkSortDirection _copyPolyline _cornerOffset _deleteTmpLine _diffAngle _doOffset _getAnglesAtParam _polyline _side *error*) (defun *error* (st) (if (wcmatch (strcase st t) "*break,*cancel*,*exit*") (redraw) (princ (strcat "\nOops! Something went wrong: ") st) ) (mapcar '_deleteTmpLine (list ent1 ent2 te0 te1 te2)) (princ) ) ;| ; Deletes an object or list of objects ; @Param obj vla-object or list |; (defun _deleteTmpLine (obj) (cond ((null obj)) ((vl-catch-all-error-p obj)) ((= (type obj) 'list) (mapcar '_deleteTmpLine obj)) ((not (vlax-erased-p obj)) (vla-delete obj)) ) ) ;| ; Draw Polyline - dexus ; Draw a polyline from a list of points, but filter out colinear points ; @Param lst list of points ; @Returns ename of polyline |; (defun _polyline (lst closed / prev pts) (while lst (cond ( (and (cdr lst) prev (or (equal (cdr lst) prev 1e-8) ; Remove duplicate points (null (inters prev (car lst) prev (cadr lst))) ; Remove collineair points ) ) ) ((setq pts (cons (cons 10 (setq prev (car lst))) pts))) ) (setq lst (cdr lst)) ) (entmakex (append (list (cons 0 "LWPOLYLINE") (cons 100 "AcDbEntity") (cons 100 "AcDbPolyline") (cons 90 (length pts)) (cons 8 (getvar 'clayer)) (cons 70 (if closed 1 0)) ) (reverse pts) ) ) ) (defun _copyPolyline (ent maxlen closed rev / bul pts index curve steps size next) (setq ent (vlax-ename->vla-object ent) index 0) (repeat (1+ (fix (vlax-curve-getEndParam ent))) (cond ( (and (not (vl-catch-all-error-p (setq bul (vl-catch-all-apply 'vla-getbulge (list ent index))))) (not (equal bul 0.0 1e-8)) (setq next (vlax-curve-getDistAtParam ent (1+ index))) (not (zerop (setq steps (fix (* (/ (- next (vlax-curve-getDistAtParam ent index)) maxlen) 45))))) ) (setq size (/ 1.0 steps) curve index) (repeat steps (setq pts (cons (vlax-curve-getPointAtParam ent curve) pts) curve (+ curve size)) ) ) ((setq pts (cons (vlax-curve-getPointAtParam ent index) pts))) ) (setq index (1+ index)) ) (_polyline (if rev (reverse pts) pts) closed) ) (defun _side (pline pnt / cpt end target der) ; https://www.theswamp.org/index.php?topic=55685.msg610429#msg610429 (setq cpt (vlax-curve-getClosestPointTo pline pnt) end (vlax-curve-getEndParam pline) target (vlax-curve-getParamAtPoint pline cpt) der (if (and (equal target (fix target) 1e-8) (or (vlax-curve-isClosed pline) (and (not (equal (vlax-curve-getStartParam pline) target 1e-8)) (not (equal end target 1e-8))) ) ) (mapcar '- (polar cpt (angle '(0 0) (vlax-curve-getFirstDeriv pline (rem (+ target 1e-3) end))) 1.0) (polar cpt (angle (vlax-curve-getFirstDeriv pline (rem (+ (- target 1e-3) end) end)) '(0 0)) 1.0) ) (vlax-curve-getFirstDeriv pline target) ) ) (minusp (sin (- (angle cpt pnt) (angle '(0.0 0.0) der)))) ) ;; Intersections - Lee Mac ;; mod - [int] acextendoption enum of intersectwith method (defun LM:intersections ( ob1 ob2 mod / lst rtn ) (if (and (vlax-method-applicable-p ob1 'intersectwith) (vlax-method-applicable-p ob2 'intersectwith) (setq lst (vlax-invoke ob1 'intersectwith ob2 mod)) ) (repeat (/ (length lst) 3) (setq rtn (cons (list (car lst) (cadr lst) (caddr lst)) rtn) lst (cdddr lst)) ) ) (reverse rtn) ) (defun _doOffset (offset / lst rtn) ; Global vars: pts ent1 ent2 sides te1 te2 (setq rtn (cond ((equal offset 0.0 1e-8) (if (setq lst (LM:intersections ent1 ent2 acExtendNone)) (setq pts (_addPoints lst ent1 ent2 pts)) ) lst ) ( (or ; Make offset (setq te1 nil) (vl-catch-all-error-p (setq te1 (vl-catch-all-apply 'vlax-invoke (list ent1 'Offset (if (car sides) offset (- offset)))))) (not (setq tmp1 (vl-some (function (lambda (te) (_checkOffset ent1 te offset))) te1))) (vla-put-visible tmp1 :vlax-false) ; (vla-put-color tmp1 252) (setq te2 nil) (vl-catch-all-error-p (setq te2 (vl-catch-all-apply 'vlax-invoke (list ent2 'Offset (if (cadr sides) offset (- offset)))))) (not (setq tmp2 (vl-some (function (lambda (te) (_checkOffset ent2 te offset))) te2))) (vla-put-visible tmp2 :vlax-false) ; (vla-put-color tmp2 252) ) (princ (strcat "\nOffset of " (rtos offset 2 4) " failed. ")) nil ) ((setq lst (LM:intersections tmp1 tmp2 acExtendNone)) (if parallel ; Add points of parallel end segments (mapcar (function (lambda (ent1 ent2) (mapcar (function (lambda (pt) (if (equal pt (vlax-curve-getClosestPointTo ent2 pt) 1e-10) (setq lst (cons pt lst)) ) )) (list (vlax-curve-getStartPoint ent1) (vlax-curve-getEndPoint ent1) ) ) )) (list tmp1 tmp2) (list tmp2 tmp1) ) ) (setq pts (_addPoints lst tmp1 tmp2 pts)) lst ) ) ) (_deleteTmpLine te1) (_deleteTmpLine te2) rtn ) ;| ; Check if the offset starts and ends at the correct point or is closed |; (defun _checkOffset (ent1 ent2 offset) (if (or (vlax-curve-isclosed ent1) (vlax-curve-isclosed ent2) (and (equal (distance (vlax-curve-getStartPoint ent1) (vlax-curve-getStartPoint ent2)) offset 1e-4) (equal (distance (vlax-curve-getEndPoint ent1) (vlax-curve-getEndPoint ent2)) offset 1e-4) ) ) ent2 ) ) (defun _addPoints (lst ent1 ent2 pts / len1 len2) (setq len1 (vlax-curve-getDistAtParam ent1 (vlax-curve-getEndParam ent1)) len2 (vlax-curve-getDistAtParam ent2 (vlax-curve-getEndParam ent2)) lst (vl-remove nil (mapcar (function (lambda (pt / d1 d2) (if (and (setq d1 (vlax-curve-getDistAtPoint ent1 pt)) (setq d2 (vlax-curve-getDistAtPoint ent2 pt)) ) (list (cons ( (lambda (ang) (if (cadr ang) (_avarageAngle (car ang) (cadr ang)))) (mapcar (function (lambda (ent) ( (lambda (ang) (if (cadr ang) (_avarageAngle (car ang) (cadr ang)))) (_getAnglesAtParam ent (vlax-curve-getParamAtPoint ent (vlax-curve-getClosestPointTo ent pt))) ) )) (list ent1 ent2) ) ) (cond ((and (vlax-curve-isclosed ent1) (not (vlax-curve-isclosed ent2))) (list (/ d2 len2))) ((vlax-curve-isclosed ent2) (list (/ d1 len1))) ((list (/ d1 len1) (/ d2 len2))) ) ) pt ) ) )) lst ) )) (append lst pts) ) ;| ; Project Point onto Line - Lee Mac ; @Param pt point to project ; @Param p1 first point of line ; @Param p2 second point of line ; @Returns projected point |; (defun LM:ProjectPointToLine ( pt p1 p2 / nm ) (setq nm (mapcar '- p2 p1) p1 (trans p1 0 nm) pt (trans pt 0 nm)) (trans (list (car p1) (cadr p1) (caddr pt)) nm 0) ) (defun _getAnglesAtParam (ent pa / ang1 ang2) (if (and (vlax-curve-isClosed ent) (= pa 0)) ; Special case for closed Polyline (setq ang1 (vlax-curve-getFirstDeriv ent 1e-14) ang2 (vlax-curve-getFirstDeriv ent (- (fix (vlax-curve-getEndParam ent)) 1e-14))) (setq ang1 (vlax-curve-getFirstDeriv ent (+ pa 1e-14)) ang2 (vlax-curve-getFirstDeriv ent (- pa 1e-14))) ) (if (and ang1 ang2) (list (angle '(0 0 0) ang1) (angle '(0 0 0) ang2) ) ) ) ;| ; Avarage Angle - dexus ; Get angle of a line between two angles ; @Param ang1 real - Angle in radians ; @Param ang2 real - Angle in radians ; @Returns real - Angle in radians |; (defun _avarageAngle (ang1 ang2 / dif) (setq dif (- ang1 ang2)) (if (< pi (abs dif)) (+ ang1 (* (- (+ pi pi) (abs dif)) (if (minusp dif) -0.5 0.5) ) ) (+ ang2 (* dif 0.5)) ) ) ;| ; Difference between angles - dexus ; Retuns the angle between two angles ; @Param ang1 real ; @Param ang2 real ; @Returns real |; (defun _diffAngle (ang1 ang2) ( (lambda (ang) (if (> ang pi) (- (+ pi pi) ang) ang ) ) (abs (- ang2 ang1)) ) ) ;| ; Check which of two poits is closer to the expected angle of the line ; @Param a (list (list angle) point) ; @Param b (list (list angle distance1 distance2) point) ; @Returns true if a is after b |; (defun _checkSortDirection (a b) (and (caar a) (caar b) (< (abs (_diffAngle (angle (cadr a) (cadr b)) (caar a))) (abs (_diffAngle (angle (cadr b) (cadr a)) (caar b))) ) ) ) ;| ; Calculate exact offset distance on a corner - dexus ; pt1 - Point on corner ; pt2 - Point on other side ; pt3 - Center for bisector ; pt4 - Target for corner of the offset ; pt5 - Find perpendicular point for offset distance ; / ; / ; -------- pt1 pt5 ; \ / ; pt4 ; \ ; ---- pt3 ----- pt2 ----- ; ; @Param ent1 Line to check corners ; @Param ent2 Opposing line ; @Returns List of offset distances (pt1 -> pt5) to calculate |; (defun _cornerOffset (ent1 ent2 / ang1 ang1a ang2 ang3 index pt1 pt2 pt3 pt4 pt5 rtn) (setq index 0) (repeat (fix (vlax-curve-getEndParam ent1)) (and (setq pt1 (vlax-curve-getPointAtParam ent1 index)) ; Point on corner (setq ang1 (_getAnglesAtParam ent1 index)) ; Angles of pt1 (setq ang1a (_avarageAngle (car ang1) (cadr ang1))) (setq te0 (entmakex (list (cons 0 "line") (cons 10 pt1) (cons 11 (polar pt1 (- ang1a halfPi) 1))))) ; Temp line for finding the angle on the other side (foreach pt2 (LM:intersections (vlax-ename->vla-object te0) ent2 acExtendThisEntity) ; Point on other side (and (setq ang2 (_getAnglesAtParam ent2 (vlax-curve-getParamAtPoint ent2 pt2))) ; Angle of pt2 (if (equal (rem (car ang1) pi) (rem (car ang2) pi) 1e-8) ; Is parallel? (and (setq parallel (or parallel (< index 1) (<= (fix (vlax-curve-getEndParam ent1)) (1+ index)) t)) ; End of line is parallel (setq pt3 (mapcar (function (lambda (a b) (* (+ a b) 0.5))) pt1 pt2)) ; Midpoint (setq ang3 (car ang1)) ; Same angle als ang1 ) (and (setq pt3 (inters pt1 (polar pt1 (car ang1) 1) pt2 (polar pt2 (car ang2) 1) nil)) ; Find center for bisector (setq ang3 (_avarageAngle (angle pt1 pt3) (angle pt2 pt3))) ; Angle of bisector ) ) (setq pt4 (inters pt3 (polar pt3 ang3 1) pt1 (polar pt1 (+ ang1a halfPi) 1) nil)) ; Find target for corner of the offset (setq pt5 (LM:ProjectPointToLine pt4 pt1 (polar pt1 (+ (car ang1) halfPi) maxlen))) ; Find perpendicular point for offset distance (setq rtn (cons (distance pt1 pt5) rtn)) ; Return offset distance ) ) ) (if (and te0 (not (vlax-erased-p te0))) (entdel te0)) (setq index (1+ index)) ) rtn ) (if (and (not (while (cond ((not (setq ss (ssget '((0 . "LWPOLYLINE"))))) (princ "\nNothing selected. Try again...\n") nil ) ((/= (sslength ss) 2) (princ "\nSelect 2 polylines! Try again...\n") ) ((and (setq org1 (ssname ss 0)) (setq org2 (ssname ss 1))) nil ; Stop loop ) ) ) ) org1 org2 ) (progn (if (not (numberp halfPi)) (setq halfPi (* pi 0.5))) (setq maxlen (* 1.1 (max (vlax-curve-getDistAtParam org1 (vlax-curve-getEndParam org1)) (vlax-curve-getDistAtParam org2 (vlax-curve-getEndParam org2)) ( (lambda (ent1 ent2 / step de1 div p_step dis dmax) (setq step (/ (setq de1 (vlax-curve-getDistAtParam ent1 (vlax-curve-getEndParam ent1))) 500) div step dmax 0.0) (while (< div de1) (setq p_step (vlax-curve-getPointAtDist ent1 div) dis (distance p_step (vlax-curve-getClosestPointTo ent2 p_step))) (if (> dis dmax) (setq dmax dis)) (setq div (+ div step)) ) dmax ) org1 org2 ) ) ) ) ; Convert first line (setq ent1 (_copyPolyline org1 maxlen (vlax-curve-isClosed org1) nil)) (setq ent1 (vlax-ename->vla-object ent1)) (vla-put-visible ent1 :vlax-false) ; Convert second line (setq ent2 (_copyPolyline org2 maxlen (vlax-curve-isClosed org2) (< (distance (vlax-curve-getStartPoint org1) (vlax-curve-getEndPoint org2)) (distance (vlax-curve-getEndPoint org1) (vlax-curve-getEndPoint org2)) ) )) (setq ent2 (vlax-ename->vla-object ent2)) (vla-put-visible ent2 :vlax-false) ; Get offset direction (setq sides (mapcar (function (lambda (a b / s m e) (setq s (_side a (vlax-curve-getStartPoint b)) m (_side a (vlax-curve-getPointAtParam b (* 0.5 (vlax-curve-getEndParam b)))) e (_side a (vlax-curve-getEndPoint b))) (or (and s m) (and s e) (and m e)) )) (list ent1 ent2) (list ent2 ent1) ) ) (mapcar ; Add half distances from closest point to every vertex (function (lambda (ent1 ent2 / index pt) (setq index 0) (repeat (fix (vlax-curve-getEndParam ent1)) (setq pt (vlax-curve-getPointAtParam ent1 index) corners (cons (* (distance pt (vlax-curve-getClosestPointTo ent2 pt)) 0.5) corners) index (1+ index)) ) )) (list ent1 ent2) (list ent2 ent1) ) (setq corners (vl-sort (append corners (_cornerOffset ent1 ent2) (_cornerOffset ent2 ent1)) '<) offsetdistance (/ maxlen 256.0)) (if (LM:intersections ent1 ent2 acExtendNone) ; For crossing polylines, add negative values (setq offset (- maxlen) corners (append (mapcar '- (reverse corners)) corners)) (setq offset 0.0) ) (setq index 0) (setq gap (getvar 'offsetgaptype)) (setvar 'offsetgaptype 0) (while (progn (while (and corners (> offset (car corners))) ; Calculated offset values to check (_doOffset (car corners)) (setq index (1+ index)) (setq corners (cdr corners)) ) (setq loop ; Incremental check (cond ((> offset maxlen) nil) ((_doOffset offset) (setq index (1+ index)) (setq start t)) ((not start) t) (start nil) ) ) (setq offset (+ offset offsetdistance)) loop ) ) (setvar 'offsetgaptype gap) (if pts ; Draw polyline (_polyline (mapcar 'cadr (vl-sort pts (function (lambda (a b / ang) (if (and (caddar a) (caddar b)) (if (< (cadar a) (cadar b)) (or (< (caddar a) (caddar b)) (_checkSortDirection a b)) (and (< (caddar a) (caddar b)) (_checkSortDirection a b)) ) (< (cadar a) (cadar b)) ) )) ) ) (and (vlax-curve-isClosed ent1) (vlax-curve-isClosed ent2) ) ) ) (_deleteTmpLine ent1) (_deleteTmpLine ent2) (if (and ent2 (not (vlax-erased-p ent2))) (vla-delete ent2)) ) ) (princ) ) River result:

Another - (defun c:test ( / e i s x ) (if (setq s (ssget "_X" '((0 . "LINE")))) (repeat (setq i (sslength s)) (setq i (1- i) e (ssname s i) x (entget e) ) (if (not (equal (cadr (assoc 10 x)) (cadr (assoc 11 x)) 1e-8)) (ssdel e s) ) ) ) (sssetfirst nil s) (princ) )

How about something like this, is that what you are looking for? (defun draw (pt1 pt2 len) (if (and pt1 pt2 len) (progn (entmakex (list '(0 . "LINE") (cons 10 pt1) (cons 11 (polar pt1 (angle pt1 pt2) len)) ) ) (entmakex (list '(0 . "LINE") (cons 10 (polar pt2 (angle pt2 pt1) len)) (cons 11 pt2) ) ) ) ) (princ) ) (draw (getpoint "\nFirst point: ") (getpoint "\nSecond point: ") (getdist "\nLine Length: ") )

Thank you Mhupp, it works like charm, I didn't know that '(equal )' would work like that, I thought that would return nil everytime, something new to learn, thank you again for your help.

ssget lines check endpoints to get angle tho not so vertical. vert.mp4 SVL.lsp

Yikes! Working with your arms tied.. No way I could work effectively without my tools, I would at least need autohotkey. Last company I worked for, I automated their whole system, mostly because I was lazy and I wanted to eat donuts all day. AutoCAD ships with .NET, nothing to install, I would be rolling some goodies for sure. “We At ACME corporation stifle innovation by making everyone think inside the box”

I post the 3d house image often and a version of that software was available for Intellicad back in the 90's, there was no VL lisp in those days. It was very good then and seen as a competitor to LT,

This was my 'Offset Inside' program: ;; Offset Inside - Lee Mac - www.lee-mac.com ;; Offsets a set of objects by a specified distance to the inside. (defun c:OffInside ( / acsel pos ) (if (and (setq *dist* (cond ( (getdist (strcat "\nOffset Distance" (if *dist* (strcat " <" (rtos *dist*) ">: ") ": ") ) ) ) ( *dist* ) ) ) (ssget '( (-4 . "<OR") (0 . "CIRCLE,ARC,ELLIPSE") (-4 . "<AND") (0 . "LWPOLYLINE,SPLINE") (-4 . "&=") (70 . 1) (-4 . "AND>") (-4 . "<AND") (0 . "POLYLINE") (-4 . "&=") (70 . 1) (-4 . "<NOT") (-4 . "&") (70 . 120) (-4 . "NOT>") (-4 . "AND>") (-4 . "OR>") ) ) ) (progn (vlax-for obj (setq acsel (vla-get-activeselectionset (vla-get-activedocument (vlax-get-acad-object)) ) ) (vl-catch-all-apply 'vla-offset (list obj (if (and (setq pos (vl-position (vla-get-objectname obj) '("AcDbPolyline" "AcDb2dPolyline"))) (LM:ListClockwise-p (LM:GroupByNum (vlax-get obj 'coordinates) (+ pos 2))) ) *dist* (- *dist*) ) ) ) ) (vla-delete acsel) ) ) (princ) ) ;; List Clockwise-p - Lee Mac ;; Returns T if the point list is clockwise oriented (defun LM:ListClockwise-p ( lst ) (minusp (apply '+ (mapcar (function (lambda ( a b ) (- (* (car b) (cadr a)) (* (car a) (cadr b))) ) ) lst (cons (last lst) lst) ) ) ) ) ;; Group by Number - Lee Mac ;; Groups a list into a list of lists, each of length 'n' (defun LM:GroupByNum ( l n / r) (if l (cons (reverse (repeat n (setq r (cons (car l) r) l (cdr l)) r)) (LM:GroupByNum l n) ) ) ) (vl-load-com) (princ)