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Deform group
These options provide controls that specify which vertices are affected by the
FFD.
Only In Volume When on, only vertices that lie inside the source volume
are deformed. Vertices outside the source volume are not affected. This is the
default choice.
All Vertices When on, all vertices are deformed regardless of whether they
lie inside or outside the source volume, depending on the value in the Falloff
spinner. The deformation outside the volume is a continuous extrapolation
of the deformation inside the volume. Note that the deformation can be
extreme for points far away from the source lattice.
Falloff This spinner, enabled only when you choose All Vertices, determines
the distance from the lattice that the FFD effect will decrease to zero. When
this spinner is set to 0, it's effectively turned off, and there is no falloff; that
is, all vertices are affected regardless of their distance from the lattice. The
units of the Falloff parameter are specified relative to the size of the lattice: A
falloff of 1 means that the effect will go to 0 for points that are a lattice
width/length/height away from the lattice (depending on which side they are
on).
Tension/Continuity Lets you adjust the tension and continuity of the
deformation splines. Although you can't see the splines in an FFD, the lattice
and control points represent the structure that controls the splines. As you
adjust the control points, you alter the splines (which move through each
point). The splines, in turn, deform the geometry of the object. By altering
the tension and continuity of the splines, you alter their effect on the object.
Selection group
These options provide additional methods of selecting control points. You
can toggle any combination of the three buttons to select in one, two, or three
dimensions at once.
All X, All Y, All Z When one of these buttons is on and you select a control
point, all control points along the local dimension specified by the button
are selected as well. By turning on two buttons, you can select all control
points in two dimensions.
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2776 | Chapter 14 Space Warps and Particle Systems