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A body is the highest level topological entity. Solid bodies contain lumps, shells, subshells, faces, loops, coedges, edges, and vertices. Wire bodies contain wires, coedges, edges, and vertices. A simple list of edges can be used to create topology, and
ACIS creates the other associated topological entities. The result is a model whose elements know about each other and the topology can be traced.
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Many operations, such as wire offsetting, utilize the features of a body topological element and the inherent ability to trace its topology through adjacent wires and edges. This is why a (wire) body is required as input to these operations.
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When a wire body is offset, sometimes gaps are created at certain junctures. Consider a wire body made up of a square and a circle that is offset towards the inside, as shown in figure 8-1. The resulting gaps can be filled as one of three types:
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Natural
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Extends the two shapes along their natural curves; e.g., along the circle and along the straight edge, until they intersect.
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Round
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Creates a rounded corner between the two segments.
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Extend
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Draws two straight lines from the ends of each segment until they intersect.
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Figure 8-1. Gap Fill Types
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In the following example, four linear edges are created. Even though the end points of each edge were picked such that the edges appeared to intersect in a simple rectangular frame, the edges are independent and know nothing about one another. In other words, the edges are separate topological entities but are not part of a topology.
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Offsetting occurs to the outside of a rectangle. By default, the wire offsetting fills the external gap using the "round" option. The result is a second wire body that is mostly rectangular except for rounded corners. The radius of the rounded corner is the wire offset amount. Refer to figure 8-2.
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Scheme Example
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; Define the positions to be used
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(define my_point1 (position 0 0 0))
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;; my_point1
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(define my_point2 (position 20 0 0))
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;; my_point2
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(define my_point3 (position 20 10 0))
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;; my_point3
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(define my_point4 (position 0 10 0))
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;; my_point4
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; Create edge 1 as a sine edge.
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(define my_linear1 (edge:linear my_point1 my_point2))
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;; my_linear1
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; Create edge 2 as a linear edge.
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(define my_linear2 (edge:linear my_point2 my_point3))
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;; my_linear2
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; Create edge 3 as a spline curve.
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(define my_linear3 (edge:linear my_point3 my_point4))
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;; my_linear3
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; Create edge 4 as a spline curve.
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(define my_linear4 (edge:linear my_point4 my_point1))
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;; my_linear4
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; Create a wire-body from a list of edges.
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(define my_wirebody (wire-body
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(list my_linear1 my_linear2 my_linear3 my_linear4)))
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;; my_wirebody
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(define my_offset (wire-body:offset my_wirebody 5 "r"))
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;; my_offset
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; If desired, you could delete the original wire body;
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; it is no longer needed.
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;(entity:delete my_wirebody)
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;; ()
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; Save the results to an output file.
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(part:save "tmpoffset1.sat")
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;; #t
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Figure 8-2. Wire Body Offset
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Some of the Scheme extensions related to wire bodies are:
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wire-body
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Creates a wire body from a list of edges.
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wire-body:kwire
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Creates a planar wire specified by a sequence of points and "bulge" factors.
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wire-body:offset
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Creates a new wire by offsetting the given wire using offset and twist laws.
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wire-body:points
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Creates a wire body from a list of positions.
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