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Action:
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Creates a new wire by offsetting the given wire using offset and twist laws.
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Filename:
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ofst/ofst_scm/woff_scm.cxx
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APIs:
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api_offset_planar_wire
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Syntax:
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(wire-body:offset wire offset-distance-law
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[twist-law] [gap-type] [trim] [direction])
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Arg Types:
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wire
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wire
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offset-distance-law
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law | real
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twist-law
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law
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gap-type
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string
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trim
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boolean
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direction
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par-pos | gvector
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Returns:
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wire
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Description:
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Assume that the planar wire body
wire, is re-parameterized to the variable
x, becoming curve(x).
T is the tangent to curve(x), and
N is a normal to the wire's plane. The double bars around the cross product
T x N and
N mean they are unitized. The offset curve to the wire body at
x is then given by the following equation.
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wire must be a planar wire body entity.
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offset-distance-law is the offset distance to use when offsetting. In the simplest case,
offset-distance-law is a constant.
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If the
twist-law is not specified, it is assumed to be 0. Thus, the offset curve becomes simply a function of the given
offset-distance-law at the curve parameter
x. In such a case and if the
offset-distance-law is a constant, the unitized cross product
T x N specifies the positive direction for the offset.
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If the
twist-law is specified, the given equation determines where the offset curve at curve parameter
x lies in three dimensional space. Twisting is about the tangent vector
T of the
wire curve and in the plane created by
T x N and
N. The
twist-law specifies the angle in the
TxN and
N plane for the offset curve. (The
twist-law evaluates to a number that is input as radians to the
cos and
sin law functions.)
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For example, if the
offset-distance-law is the constant 2 and the
twist-law is simply the law function "x", then the result is a helix of radius 2 that winds around
wire.
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gap-type is a string that specifies how to fill in gaps created by offsetting; valid strings are "N" for "natural", the default (2), "R" for "round" (0), and "E" for "extend" (1). Consider the wirebody made up of a square and a circle, as shown. When this wirebody is offset, a gap is created at certain junctures. "natural" extends the two shapes along their natural curves, e.g., along the circle and along the straight edge, until they intersect. "round" creates a rounded corner between the two segments. "extend" draws two straight lines from the ends of each segment until they intersect. The default is "natural."
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trim is an optional argument specifying whether or not to repair the self intersecting wire.
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direction specifies the plane normal to be used for offsetting the non-planar wires.
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Limitations:
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Non-constant offset laws and non-zero twist laws are not supported by the gap fill feature and may not produce the desired results.
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Example:
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; wire-body:offset
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; Create a wire-body by offsetting a wire by
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; a given distance.
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; Create edge 1.
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(define edge1
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(edge:circular (position 10 0 0) 10))
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;; edge1
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; Create a wire-body from the edges.
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(define wirebody1 (wire-body (list edge1)))
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;; wirebody1
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; OUTPUT Original
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; Offset a wire-body outside the original wire-body.
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(define offset (wire-body:offset wirebody1 5 "2*x"))
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;; offset
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; OUTPUT Result
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Figure 2-3. wire-body:offset
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; Another example using laws.
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(part:clear)
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;; #t
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(define edge1 (edge:circular (position 0 0 0) 20))
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;; edge1
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; OUTPUT Original
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(define wirebody2 (wire-body edge1))
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;; wirebody2
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(define offset1
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(wire-body:offset wirebody2
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"20+10*cos(x*10)"))
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;; offset1
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; OUTPUT Result
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Figure 2-4. wire-body:offset - Using Laws to Define Geometry
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