Graphics Reference
In-Depth Information
Fig. 14.27 The red edge in the center object is a cusp, a non-tangent edge boundary. On right , no
edge boundary is visible because the edges are tangent
Fig. 14.28 The two patches on left are curvature continuous on right because each has two rows
of CVs beside the edge that are lined up in a 180° angle
representation of a surface, but it is more than that, because it is possible to make a
surface using nothing but points that lie on the surface without achieving correct
surface tension.
14.4.9
Tangent Surfaces
Tangent surfaces, like tangent curves, are surface pairs whose incoming and outgo-
ing tangents along common boundaries have the same value. When non-tangent
surfaces meet, a cusp is formed (Fig. 14.27 ). A cusp is a hard edge along a non-
tangent boundary.
14.4.10
Curvature Continuity
Curvature continuity is similar to tangency, but to a greater degree. Instead of tan-
gency being held by one control vertex on either side of the respective endpoints of
two curves, there is a minimum of two control points with matching tangents on
either side of the join (Fig. 14.28 ). This increases the strength of tangency at this
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