Abstract: A method of automatically operating a machine with respect to an object having a desired profile, wherein the machine's operation is controlled based on a model of the object's profile. The method includes generating at least a portion of the model in the form of a plurality of successive layers wherein the cross-section of each layer is defined by the intersection of a pair of parallel planes and a model profile connecting the parallel planes. Each layer's thickness is selected such that the geometrical error between the object's desired profile and the model profile of the layer remains no greater than a preselected geometrical error. More than one layer thickness is selected during the step of generating this portion of the object. The machine can be operated in successive steps with each step based on a separate one of the layers.