helper function to create an object to be processed by vcgRaySearch
create a search structure from a matrix of coordinates and one of directional vectors to be processed by vcgRaySearch
k x 3 matrix (or a vector of length 3) containing the starting points of the rays
k x 3 matrix (or a vector of length 3) containing the directons of the rays. The i-th row of
an object of class "mesh3d" (without faces) and the vertices representing the starting points of the rays and the normals storing the directions.