Find on which side of a curve a point exists

Hi @dale
Is there Api for Curve side(Similar this grasshopper component){for open curve}
In c#?

I don t think so.

you will need a reference plane / normal / z-vector to judge this

if you implement your own function:

P the point to evaluate
S the closest point on the curve
t the corresponding parameter on the curve
you can use
https://developer.rhino3d.com/api/RhinoCommon/html/Overload_Rhino_Geometry_Curve_ClosestPoint.htm

to get the t
get S and tangent

now calculate a curve normal in respect of the plane / z-Vector
(project to cplane, Cross Product)
compare it to the PS vector
get the angle between the PS vector and the curve normal
angle < 90 degree => left

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