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ACIS supports these general types of curves:
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Analytic curve
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A simple curve that can be wholly represented by a simple algebraic formula. Simple analytic geometry can generally be analyzed up to, but not beyond, the fourth degree equation.
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Interpolated curve
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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 instead by reference to other geometric entities.
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The
curve class is the base construction geometry class for curves, and other curve construction geometry classes are derived from it. The
curve class is abstract construction geometry, while its children are specific construction geometry.
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The following classes are derived from the
curve class:
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straight
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Position plus direction. The magnitude is stored, but it is always 1.
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The equation of a straight line, for instance, is:
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Pt = P + t*dir
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Where
P is the root
position,
dir is a
direction vector,
t is a parameter for the curve space, and
Pt is the 3D
position of the parameter
t on the line.
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ellipse
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Represents ellipses. A circle is a special type of ellipse.
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intcurve
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Represents an interpolated curve. Any curve that cannot be expressed as an ellipse or a straight line can be expressed as an interpolated curve.
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degenerate_curve
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This special curve class is used by skinning and lofting. It is intended to provide a way to build skin or loft surfaces that come to a point at either end.
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undefc
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This special curve class denotes a curve that is undefined except for its end points, for which there are explicit positions, directions, and curvatures.
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There are model geometry classes (with uppercase names) that correspond to these construction geometry classes. The
CURVE class is the base model geometry class for curves, and other curve model geometry classes are derived from it. The
CURVE class is abstract model geometry, while its children are specific model geometry.
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