3D modeling
3-D modeling is the use of software to create a virtual three-dimensional model of some physical object.
3-D modeling is used in many different industries, including
virtual reality , video games, 3D printing , marketing, TV and motion pictures,
scientific and medical imaging and computer-aided design and manufacturing CAD/CAM .
3-D modeling software generates a model through a variety of
tools and approaches including:
Simple
polygons.
3-D
primitives -- simple polygon-based shapes, such as pyramids, cubes,
spheres, cylinders and cones.
Spine
curves.
NURBS (non-uniform rational b-spine) --
smooth shapes defined by bezel curves, which are relatively
computationally complex.
2-D geometric polygon shapes are used extensively in motion
picture effects and 3-D video game art. Creating approximations of
shapes made with polygons is much more efficient in raster graphics , which are required for real time
3-D gaming.
In art for video games and motion picture effects, a model
might start as a rough-out using polygon primitives or NURBS, or as a design
made by following contours on multiple 2-D isometric views. If the model is to
be animated, careful consideration of the arrangement of continuous edge loops must
be maintained in the models polygons around areas of deformation such as
joints. A model that looks good stationary will fold faster than Superman
laundry in animation when the appearance of the stationary end model is all
that’s considered during building.
Once a model is adequately built, an artist might arrange
the coordinates of the model to match its 2-D
textures in a process called UV mapping, a process that is kind of like trying
to design and tailor with a computer mouse. Areas that require more detail are
given more space in the UV map. This can be done either using a repeating
texture such as a checker board as a place holder or by using an existing
texture.
Generally the next step might be to texture the model, which
is to apply either hand-painted or photograph-based 2-D images, usually TGA (Tara bitmap), to the model that will define:
Its
color with a color map.
Its
reflectivity and reflected color with a secular map.
Its
surface texture, defined through light-play with a bump or normal map, or
a deformation map for actual added geometric detail.
Animated models require an extra step of rigging, which is
like giving them a virtual skeleton with bones and joints along with the controllers to manage it. The way the texture of
these joints influences the surface texture under deformation must be defined
in skinning, where one paints the weight of joint influence on the textures
directly on the models polygons; a polygon painted more heavily is more heavily
influenced by a selected joints movement. The model is then ready for the
animator.
More computational and expensive methods of making models such
as NURBS may be used, along with complex shades that interact with
particle-based light, in rendered graphics when real time is not a necessity.
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