1. A method for modifying a representation of a surface by a computational machine, comprising: first accessing, by the computational machine, first surface data defining a first surface in a coordinate space having three dimensions, and curve data defining a curve in the coordinate space the data curve dependent upon coordinates of points of the first surface so that the curve follows a path in the first surface within a predetermined measurement of tolerance relative to the coordinate space; second accessing, by the computational machine, geometric object data for defining a geometric object, the geometric object data determined using data indicative of tangents to said first surface at, or approximately at, corresponding points on said first curve; changing, by computer operations of the computational machine, the geometric object data so that coordinates of points of a portion of the geometric object changes relative to coordinates of points of the first curve in the coordinate space; and determining, by computer operations of the computational machine, a different contour of an interior of said first surface, wherein the different contour is determined as a function of the changed geometric object data, and for the coordinate space, the path is effectively in the first surface having the different contour.