Topic: Point offset in Polyline

[FELIX]

From a selected polyline and an informed distance X I select a point P1.
I want to have a point P1A and P1B as an offset.

[Lee Mac]

The easiest approach is to make use of the various vlax-curve-* functions, specifically: vlax-curve-getclosestpointto (to obtain a point on the polyline, given a point obtained from the user), vlax-curve-getparamatpoint (to determine the parameter of the point returned), & vlax-curve-getfirstderiv (to obtain the tangent vector at the given point).

From the tangent vector, you can calculate a perpendicular vector which may be scaled by the distance 'X', or alternatively, you can calculate the angle of the tangent vector, add/subtract pi/2 radians, and calculate the offset points using the polar function.

[BIGAL]

Like Lee, for distance along a pline use  (vlax-curve-getpointatdist obj len)

[xdcad]

The easiest approach is to make use of the various vlax-curve-* functions, specifically: vlax-curve-getclosestpointto (to obtain a point on the polyline, given a point obtained from the user), vlax-curve-getparamatpoint (to determine the parameter of the point returned), & vlax-curve-getfirstderiv (to obtain the tangent vector at the given point).

From the tangent vector, you can calculate a perpendicular vector which may be scaled by the distance 'X', or alternatively, you can calculate the angle of the tangent vector, add/subtract pi/2 radians, and calculate the offset points using the polar function.

Use code to translate the master’s words:

Code - Auto/Visual Lisp: [Select]

1. ;|
2. Suitable for calculating point offset on any curve
3. single point
4. |;
5. (defun XD::Curve:OFSPnt (e pnt offsetx / pnt xdir ydir mat)
6.   (setq pnt  (xdrx-getpropertyvalue e "getClosestPointTo" pnt)
7.                                         ; closest point
8.         xdir (xdrx-getpropertyvalue e "firstderiv" pnt)
9.                                         ; tangent vector
10.         ydir (xdrx-vector-perpvector xdir) ;vertical vector
11.         mat  (xdrx-matrix-settranslation
12.                (xdrx-vector-product ydir offsetx)
13.                                         ; translation transformation matrix
14.              )
15.   )
16.   (list (xdrx-point-transform pnt mat)  ; The transformation matrix is applied to the point
17.         (xdrx-point-transform pnt (xdrx-matrix-inverse mat))
18.   )
19. )
20. ;Multiple points, point table to find offset points
21. (defun XD::Curve:OFSPnts (e pnts offsetx / pnt xdir ydir mat)
22.   (mapcar '(lambda(x)(xd::curve:ofspnt e x offsetx)) pnts)
23. )

[kdub_nz]

@xdcad,

should the pnts parameter passed in be pnt ??
because of the 
(xdrx-getpropertyvalue e "getClosestPointTo" pnt)

(defun XD::Curve:OFSPnts (e pnts offsetx / pnt xdir ydir mat)

For Interest,
Why do you think the xdrx-xx method is better than the ActiveX method

Code - Auto/Visual Lisp: [Select]

1. (vlax-curve-getClosestPointTo curve-obj givenPnt [extend])

https://help.autodesk.com/view/OARX/2023/ENU/?guid=GUID-90F585FE-D5C8-4C08-AFC7-A09A697EA52A

or using

Code - Auto/Visual Lisp: [Select]

1. (vlax-get-property object property)

https://help.autodesk.com/view/OARX/2024/ENU/?guid=GUID-B3F22E35-4666-452F-89C8-5BC15B9E9463

[xdcad]

@xdcad,

should the pnts parameter passed in be pnt ??
because of the 
(xdrx-getpropertyvalue e "getClosestPointTo" pnt)

(defun XD::Curve:OFSPnts (e pnts offsetx / pnt xdir ydir mat)

For Interest,
Why do you think the xdrx-xx method is better than the ActiveX method

Code - Auto/Visual Lisp: [Select]

1. (vlax-curve-getClosestPointTo curve-obj givenPnt [extend])

https://help.autodesk.com/view/OARX/2023/ENU/?guid=GUID-90F585FE-D5C8-4C08-AFC7-A09A697EA52A

or using

Code - Auto/Visual Lisp: [Select]

1. (vlax-get-property object property)

https://help.autodesk.com/view/OARX/2024/ENU/?guid=GUID-B3F22E35-4666-452F-89C8-5BC15B9E9463

It doesn’t matter which method is better, XDRX or ActiveX
As long as it can catch mice, it's a good cat

XDRX API communicates directly with ARX, ActiveX needs to "go around a little further"
XDRX API is developed in applications, mainly to solve problems and be more "humane"

The LISP code written by XDRX is closer to the thinking of C++ ARX.
Including the processing methods of matrices, vectors, etc., regardless of efficiency, ARX is better in terms of legibility.
Because it is closer to a mathematical solution

In LISP, brackets within brackets make it difficult to see the logic clearly in many codes.

All roads lead to Rome

As for whether XDRX is good or bad, using it more may pay more attention to understanding.

XDRX API is the programming package of C++ ARX. In many cases, it is how to write C++ (ARX), and XDRX API is directly translated into LISP.