Question

I have a point, and a point normal defined to it. Suppose I also have a polydata, which doesn’t include or span this point.

I want to find the distance from this point to the polydata along the polydata normal. By distance, I mean how far should I translate the point so that it “touches” the surface defined by polydata.

Is this possible to do with vtk?

Answer 1

First I am not expert on vtk or any engine package. But your first question is a pure geometric one. Firstly you should compute the plane that polydata lies on it as a point(PlaneDefPoint) in that plane and a plane normal(PlaneDefNormal).
You may compute it by calculation of cross product of two vectors obtained from three point lies on that plane (in this case three points from your polydata).

                   *  Point
PlaneDefNormal    /
               ^ /               
               |/
---------------*-------------------  Plane
         PlaneDefPoint

After you obtain plane definitions. Compute vector to the point from the definition point of plane (PlaneDefPoint) and calculate dot product of this vector(inclined one in the figure) with the plane normal(PlaneDefNormal).