Abstract: A device for automating operation of a stereolithography apparatus uses an STL file as an input and includes a programmable computer, a facet processor that sorts the facets of the STL file according to a predetermined slice axis. The facet processor also groups the sorted facets according to those having common minimum vertex values with respect to the slice axis. The facet processor also subgroups the grouped facet file according to facets having common maximum vertex values with respect to the slice axis. A key characteristic identifier identifies key characteristics of the STL file. A thickness calculator determines the thickness of each layer of the model according to a geometrical error of preselected magnitude. A slicer calculates the intersection of each sliced plane by the calculated thickness. A directional ordering device insures uniformity with the direction of each other contour that defines the intersection.