def fnCalculate_Coords_Line3D(direction_vec,pos_line,mu):
    """
    Calculates coordinates of a point on a line in 3D.
    direction_vec is the direction vector of the line
    pos_line is the position vector of a point on the line.
    mu is the free parameter which determines the coordinates of the desired
    point on the line.
    
    Created: 26/04/17 in testplanetransformations.py
    """
    pos_new = pos_line + mu*direction_vec;
    return pos_new