Point on Left or Rigth side of Line

I was going to swear I’ve done this, but now I can not seem to figure out how I can do it.

So, I have a Line, and some points.

I want select a point and check if the selected point is on Left or Rigth side of line.

Any Simple way?


If you define a plane that has its normal in the direction of the outer product of the line direction and normal of the plane where the points are in, you can use the signed distance function https://developer.rhino3d.com/api/RhinoCommon/html/M_Rhino_Geometry_Plane_DistanceTo.htm

Thank you,

There is any way without mess with planes?

How can you determine side without a plane? A line itself has no sides unless it is related to a plane.

I dont know, maybe usind the startpoint line endpoint line ?? Just asking.


Here’s a sound strategy that was proposed to me a couple of days ago:

End points have nothing to do with side. That still does not give the line a side, think about it geometrically. Imagine a cylinder, how would you determine the side of a cylinder since it has no faces? It is just one continuous wrapped around face, until you introduce an orienting plane. A line has the same problem. You need atleast a base plane to orient the line to have sides. Is your line always 2d? If so, then the plane in that case would be the line itself as a planes X axis and the world Z as the planes Y axis.

For instance, Grasshopper has a curve side component for this that will also require a plane. In the case of a 2d line on the World XY axis you just need the base plane (World XY).