Test whether a curve in space is concave or convex?

I found this thread

And the solution provided by Danny seems to work, but the old deconstruct component had the plane coordinate system as an input. Now it doesn’t.

I need to test whether if the mid point of the curve has positive or negative value in respect to the plane of the start point.

But its not working ok, as both values seem to be positive…

Concave or Convex.gh (14.2 KB)

You can use Plane Coordinates if you want to know the UVW coordinates of an XYZ point in a specific plane.

If you only want to measure whether a point is above or below a plane, then the Plane Closest Point component can help as well. It has a distance output which will be negative if the point is below the plane.

Thank you David that was it.

@DavidRutten approach is much easier, but just in general: Usually “left-right” checks are done by evaluating the dot between a plane normal and the vector from point minus plane origin. Might be a bit overcomplicated here against "plane closest poin"t, but f.e. in scripts this isn’t a big deal.