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Introduction to Continuity TerminologyContinuity is the term
used in Alias to describe how surface patches meet. Here, a fillet
blend is used as an example:
How CVs Control ContinuityContinuity is achieved by controlling
the CVs at the edge of the aligned curve or surface. A higher
continuity levelrequires more CVs to be aligned.
Here is an example of both a curve and a surface being matched
at different continuity levels:
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Continuity Between Two Curves or SurfacesA circular (G1) fillet
is specified simply by a radius value. But because G2 and G3
fillets aren't circular, then they need adifferent way of
specifying their size.
The first technique is Radius which keeps a fixed radius
(allowing a variable width), and then specifies the size in
twoways:
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The second technique is Chord which keeps a fixed width
(allowing a variable radius), and again there are two ways
tospecify the size of the fillet:
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Form FactorThe main determinant of shape is the continuity level
chosen (G1, G2 etc.), but there is some flexibility within
thatprovided by the Form Factor. This controls the concentration of
CVs towards or away from the centre of the blend,making the curve
sharper or flatter.
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Colinear and Non-Colinear AlignmentThe easiest way to get
surfaces matching smoothly is when you have:
Two natural (untrimmed) surface edges to be aligned.
The surfaces have the same degree and spans in the direction of
the joint edge.
These are called colinear surfaces, and when using the Object
Edit Align tool then the Alignment Type : Edge shouldbe used:
As the design progresses and you need to build more complex
transitions, you will have non-colinear situations whereyou
are:
Aligning to the interior of a surface, or
Aligning to a trimmed edge.
When using the Object Edit Align tool, the options should be set
to : Alignment Type : Project.
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Other tools like Bi-Rail, Square and Freeform Blend will work in
non-co-linear situations, but typically produce heaviersurfaces
with more spans, which may be unevenly spaced.
Continuity TolerancesContinuity is calculated to a certain
tolerance or accuracy. This can be set in the Construction options
window and areusually chosen to match the CAD system you expect to
be exporting your data to.
Tools that Achieve Continuity
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Example:
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