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The internal mechanics for etch plotting are the same as for color plotting. The ray tracing is computed as for a color plot, but instead of defining a pixel color immediately, the surface numbers corresponding to each pixel are saved. After completion of the ray tracing, the surface array is scanned in a search for neighboring pixels with different surface numbers. A line is drawn connecting such pairs of pixels. The body primitives are rendered since they consist of distinct surfaces. The image that results is similar to a line drawing, but has limited resolution due to the discrete pixels. Unlike line drawings, ETCH can handle most MCNP surface geometries.
Additional quantities are checked for change when repeated structures are present. If the surface is part of a universe contained within another cell, the cell numbers of the containers are checked. Only the number of the immediate container is checked, so some boundaries may be missed when multiple fill levels exist. The lattice element number is checked when inside a lattice. The ETCH image will show the boundaries of the elements on surfaces within a lattice, such as when a cutter body exposes the interior. The boundaries will not be shown on the surface of a cell that is filled with a lattice; that surface is not within the lattice.