I am developing a plugin and I would like to be able to store data relevant to my plugin on an individual vertex in a polyline.
I could keep a map around that maps index to data, but that would fall apart if the user adds more vertices. I could also generate a new point and store data associated with that points, but that falls apart if the user moves the polyline.
You cannot store “user” data on a polyline vertex. However, you can store user data on a Rhino.Geometry.PolylineCurve, as it has the proper class inheritance. Perhaps you can maintain a array parallel with the object’s internal Rhino.Geometry.Point3d array.
There are a couple of ways of storing user data on objects. Here is some reading to get you started.
And here is a sample project that demonstrates user data.