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This section defines some types of curves and surfaces that are discussed in this chapter. For more information on curves and surfaces, refer to Chapter 7,
Curves and Surfaces.
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Analytic refers to a simple curve or surface that can be wholly represented by a simple algebraic formula. Analytic curves include straight lines and ellipses (including circles, which are simply special forms of ellipses). Analytic surfaces include cones (including cylinders, which are special forms of cones), planes, spheres, and tori. Some analytic surfaces, such as ellipsoids, are implemented in
ACIS as splines.
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Compositerefers to a curve that is an ordered list of analytic and/or interpolated curves.
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Interpolated refers to a curve that is the general representation of any curve that is not defined in
ACIS by one of the analytic curves (i.e., by an explicit "equation"), but by reference to other geometric entities. Examples include the intersection of two surfaces, a spline curve (2D or 3D B-spline), and a silhouette curve. An interpolated curve is also called an
intcurve.
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Mesh refers to a surface composed of an array of tessellations, or facets, suitable for lightweight processing of very large amounts of data, such as are used by geophysical modeling applications.
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Parameter space curve (pcurve) refers to a mapping of a 2D curve onto a 3D surface.
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Spline refers to a curve or surface that cannot be directly represented in
ACIS by one of the simple analytic surfaces (i.e., by a simple analytic formula), but that can be indirectly represented by an ordered list of analytic formulae, by segmenting the curve or surface with control points.
ACIS implements some analytic surfaces, such as ellipsoids, as splines.
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