Topic: How to determine a point is on the left of right of Pline

[donwynne]

I have a Point (PT1) and a Pline, always exist a Line accross PT1 and perpendicular with Pline
How to know a Point is on the left or Right of Pline by autolisp?
Please help.
Thank all.

[Jeff_M]

I have some code to share but I cannot post a reply with it included until you have made a few more posts.

[VovKa]

https://www.theswamp.org/index.php?topic=57171.0

[Jeff_M]

FYI, both of the methods offered in the link VovKa provided fail to work correctly when the polyline segment and pt are near the X-axis 0/360 angle or if the polyline segment is an arc.

[ribarm]

FYI, both of the methods offered in the link VovKa provided fail to work correctly when the polyline segment and pt are near the X-axis 0/360 angle or if the polyline segment is an arc.

Haven't tested, but should be OK - based on provided link...

Code - Auto/Visual Lisp: [Select]

1. (defun c:pt-curve-side ( / pt ent )
2.  
3.   (vl-load-com)
4.  
5.   (setq pt  (trans (getpoint "\nPoint : ") 1 0)
6.         ent (car (entsel "\nCurve : "))
7.   )
8.  
9.   (if (minusp (sin (- (angle (vlax-curve-getclosestpointto ent pt) pt) (angle '(0.0 0.0) (vlax-curve-getfirstderiv ent (vlax-curve-getparamatpoint ent (vlax-curve-getclosestpointto ent pt)))))))
10.     (prompt "\nPoint is on left side of picked curve...")
11.     (prompt "\nPoint is on right side of picked curve...")
12.   )
13.   (princ)
14. )
15.