Graphics Reference
In-Depth Information
Fig. 14.8
Curves
A
and
B
are tangent to each other because their tangents are equal at their
endpoints
14.2.1.4
Edit Points
Like vertices, edit points are embedded in the curves they are a part of. Edit point
positions exert a comparatively stronger infl uence on curves than CVs. Edit points
are made of
knots
in the curve. The number of knots determines the strength of
the infl uence.
14.2.1.5
Isoparms
An isoparm is a coordinate in the local space of the curve. There are as many
isoparms as there are numbers to defi ne them with, but for practical reasons they are
only displayed if requested by the user. When displayed, knots and a CV are added
to the curve so that it may be edited.
14.2.2
Parametric Curves
Although all curves in any CAD program are splines of some kind, they are not all
defi ned at the user-interface level by laying down control points with your mouse.
Arcs and circles can be defi ned parametrically and are very useful because it is more
diffi cult to generate curves of this type by hand. A two-dimensional arc can be plotted
in a number of ways. These are the most common:
•
Radius and center point
•
Radius, center point, and arc length
•
Two points and center
•
Three points on curve
•
Tangent to two curves or surfaces
•
From point to tangent to a curve or surface
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