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1201

1182 Chapter 9: Sur face Modeling

Setting the degree greater than 3 isn’t

recommended, because hig her degrees are slower

to calculate and less stable numerically. Higher

degrees are suppor ted primarily to be compatible

with models created using other surface modeling

programs.

The number of CVs in a given dimension must be

at least one g reater than that dimension’s deg ree.

Automatic Reparameterization group

Theradiobuttonsinthisgroupboxletyou

choose automatic reparameterization. With

reparameterization, the surface maintains

its parameterization as you edit it. Without

reparameterization, the surface’s parameterization

doesn’t change as you edit it, and can b ecome

irregular.

None—Do not reparameterize.

Cho rd L e n g t h —Chooses the chord-length

algorithm for reparameterization.

Chord-length reparameterization spaces knots

(in

parameter space (page 3–1082)

)basedonthe

square root of the length of each curve segment.

Chord-length reparameterization is usually the

best choice.

Unifor m—Spaces the k nots uniformly.

A uniform knot vector has the advantage t hat the

surface will change only locally when you edit it.

With the other two forms of parameterization,

moving any CV can change the entire surface.

The close controls let yo u close a surface. They

appear on the Point Surface rollout while an

independentpointsurfacesub-objectisselected.

They have no effect if the surface is already closed

in that direction.

Close R ows —Closes the surface by joining the ends

of its rows.

Close Cols . —Closes the surface by joining the ends

of its columns.

Rebuild—Displays the

Rebuild CV Surface dialog

(page 1–1237)

, which lets you specify how to

rebuild the surface. Rebuilding the surface can

change its appearance.

Reparameterize—Displays the

Reparameterize

dialog (page 1–1238)

. Reparameterizing a surface

changes the surface’s

parameter space (page

3–1082)

to provide a better relation between

control point locations and the shape of the

surface.

Tip: It is a good idea to reparameterize after you

have added CVs to the sur face by refining or

inserting.

Poi nt S urf a ce S u b-Obj e ct

Select NURBS object. > Modify panel > Create Surfaces

rollout > Point Surf

Select N URBS obj ect. > Modify pane l > NURBS toolbox >

Create Point Surface button

Selec t NURBS object. > Modify panel > R ight-click a

viewport. > Tools 2 (lower-left) quadrant > Create Point

Sur face

Point surface sub-objects are similar to object-level

point surfaces (page 1–1103)

.Thepointsare

constrained to lie on the surface.