Modeling The process of creating 3D Objects

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ModelingThe process of creating 3D Objects

• Polygon Modeling
• NURBS Modeling
• Subdivision Surfaces

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Pipeline
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Modeling In A Studio Pipeline
In a studio environment, sculptors create
maquettes to work out the shape of 3D models.
This process is especially useful during
character development to define the character
shape before CG modeling begins.
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Surface Normals
A surface normal is a 3D vector that is
perpendicular to a surface. Surface normals are
used extensively during lighting calculations.
During modeling surface normals can be modified
or flipped which can cause problems further
down the pipeline.
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Plans Production Drawings
Production drawings and schematics are used as
guides during modeling. In some cases the art
director has a clear picture of how they want a
model to look. If they have supplied production
art, the modeling artist can work directly from
the artwork.
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Level Of Detail
During the modeling process it is important to be
aware of what the final output will be for the
model. This includes how detailed the model
needs to be for the production. A model used in
a video game production will have much less
detail that a model that will be used in a
feature film.
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Plan of Attack
It is important to have a plan of attack when
modeling. This generally includes deciding what
type of modeling approach you are going to use
and what modeling tools you are going to need.
Especially for more detailed models, planning
ahead can prevent you from redoing work over and
over.
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Polygon Primitives
Maya gives the user a starting point with a
number of primitive polygon models. These are
the primitive polygon models available in Maya.
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Valence
Vertex Valence is defined as the number of edges
that meet at a vertex.
All vertices of a cube are have a valence of 3
All vertices of this object have a valence of 4
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Polygon Components

• Vertex a point at the corner of a polygon
• Edge a line connecting 2 vertices of a polygon
• Face a surface created from 3 or more vertices

Edge
Face
Vertices
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Polygon ModelingVertex Faces
In addition to saving all the vertex information
for a polygon shape, Maya stores the vertex
information for each individual face. This can be
especially useful during texturing.
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Extrusions
One common method of modeling polygons is by
extruding faces to build geometry. This process
involves selecting a polygon face and pushing
the face outward in the direction of the surface
normal to create new geometry.
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Booleans
Boolean operations create new geometry based on
the relationship of two or more objects that have
overlapping geometry. After a Boolean operation
has been applied to two objects a new set of
geometry is created. Boolean operations can
create unclean geometry which can cause problems
during rigging and lighting.
B
A
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Booleans
A Union B
B Difference A
A Intersect B
A Difference B
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Polygon Modeling
One advantage of polygon modeling is the that the
final model is one piece of geometry. This is
especially useful for character animation due to
the fact that a character setup artist can apply
deformations to the entire model without worrying
about seams.
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Subdivision
In order to given a polygon model more detail it
is sometimes necessary to subdivide faces to add
more surface detail. This process generally is
used to refine a rough shape into a more detailed
smoother surface. In Maya the polygon subdivide
face tool creates a more detailed mesh without
attempting to smooth the model. The polygon
smooth tool adds more detail and smoothes the
polygon model using the Catmull-Clark subdivision
scheme.
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Subdivision
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Catmull-Clark Subdivision Scheme
The smooth operation in Maya applies the
Catmull-Clark Subdivision scheme to polygon
models. When the Catmull-Clark subdivision
scheme is applied to a polygon mesh a face point
is created in the center of all faces, and an
edge point is placed at the center of all edges.
The Catmull-Clark subdivision scheme produces
only quadrilaterals which is extremely useful
when texturing..
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Alternative Subdivision Schemes
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Doo-Sabin Subdivision Scheme
The Doo-Sabin subdivision scheme produces only
valence 4 vertices.
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Bevel
Polygon models by definition have straight edges.
In order to create realistic objects, modeling
artist often have to smooth the corners or bevel
polygon models. Beveling a polygon model adds
detail to the sides of a object in order to
create a rounded edge.
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Bevel