In 3D computer graphics, 3D modeling (or modelling) is the
process of developing a mathematical representation of any three-dimensional
surface of an object (either inanimate or living) via specialized software. The
product is called a 3D model. It can be displayed as a two-dimensional image
through a process called 3D rendering or used in a computer simulation of
physical phenomena. The model can also be physically created using 3D printing
devices.
Models may be created automatically or manually. The manual
modeling process of preparing geometric data for 3D computer graphics is
similar to plastic arts such as sculpting.
3D modeling software is a class of 3D computer graphics software
used to produce 3D models. Individual programs of this class are called
modeling applications or modelers.
Contents
1 Models
2 Modelling process
3 Compared to 2D
methods
4 3D model market
5 3D printing
6 Human models
7 Uses
8 See also
9 References
10 External links
Models
3D models represent a 3D object using a collection of points in
3D space, connected by various geometric entities such as triangles, lines,
curved surfaces, etc. Being a collection of data (points and other
information), 3D models can be created by hand, algorithmically (procedural
modeling), or scanned.
3D models are widely used anywhere in 3D graphics. Actually,
their use predates the widespread use of 3D graphics on personal computers.
Many computer games used pre-rendered images of 3D models as sprites before
computers could render them in real-time.
Today, 3D models are used in a wide variety of fields. The
medical industry uses detailed models of organs; these may be created with
multiple 2-D image slices from an MRI or CT scan. The movie industry uses them
as characters and objects for animated and real-life motion pictures. The video
game industry uses them as assets for computer and video games. The science
sector uses them as highly detailed models of chemical compounds. The
architecture industry uses them to demonstrate proposed buildings and
landscapes through Software Architectural Models. The engineering community
uses them as designs of new devices, vehicles and structures as well as a host
of other uses. In recent decades the earth science community has started to
construct 3D geological models as a standard practice. 3D models can also be
the basis for physical devices that are built with 3D printers or CNC machines.
Almost all
3D models can be divided into two categories.
Solid - These models define the volume of the object they
represent (like a rock). These are more realistic, but more difficult to build.
Solid models are mostly used for nonvisual simulations such as medical and
engineering simulations, for CAD and specialized visual applications such as
ray tracing and constructive solid geometry
Shell/boundary - these models represent the surface, e.g. the
boundary of the object, not its volume (like an infinitesimally thin eggshell).
These are easier to work with than solid models. Almost all visual models used
in games and film are shell models.
Because the appearance of an object depends largely on the
exterior of the object, boundary representations are common in computer
graphics. Two dimensional surfaces are a good analogy for the objects used in
graphics, though quite often these objects are non-manifold. Since surfaces are
not finite, a discrete digital approximation is required: polygonal meshes (and
to a lesser extent subdivision surfaces) are by far the most common
representation, although point-based representations have been gaining some popularity
in recent years. Level sets are a useful representation for deforming surfaces
which undergo many topological changes such as fluids.
The process of transforming representations of objects, such as
the middle point coordinate of a sphere and a point on its circumference into a
polygon representation of a sphere, is called tessellation. This step is used
in polygon-based rendering, where objects are broken down from abstract
representations ("primitives") such as spheres, cones etc., to
so-called meshes, which are nets of interconnected triangles. Meshes of
triangles (instead of e.g. squares) are popular as they have proven to be easy
to render using scanline rendering. Polygon representations are not used in all
rendering techniques, and in these cases the tessellation step is not included
in the transition from abstract representation to rendered scene.
Modelling
process
There are three popular ways to represent a model:
Polygonal modeling - Points in 3D space, called vertices, are
connected by line segments to form a polygonal mesh. The vast majority of 3D
models today are built as textured polygonal models, because they are flexible
and because computers can render them so quickly. However, polygons are planar
and can only approximate curved surfaces using many polygons.
Curve modeling - Surfaces are defined by curves, which are
influenced by weighted control points. The curve follows (but does not
necessarily interpolate) the points. Increasing the weight for a point will
pull the curve closer to that point. Curve types include nonuniform rational
B-spline (NURBS), splines, patches and geometric primitives
Digital sculpting - Still a fairly new method of modeling, 3D
sculpting has become very popular in the few years it has been around.[citation
needed] There are currently 3 types of digital sculpting: Displacement, which
is the most widely used among applications at this moment, volumetric and
dynamic tessellation. Displacement uses a dense model (often generated by
Subdivision surfaces of a polygon control mesh) and stores new locations for
the vertex positions through use of a 32bit image map that stores the adjusted
locations. Volumetric which is based loosely on Voxels has similar capabilities
as displacement but does not suffer from polygon stretching when there are not
enough polygons in a region to achieve a deformation. Dynamic tesselation Is
similar to Voxel but divides the surface using triangulation to maintain a
smooth surface and allow finer details. These methods allow for very artistic
exploration as the model will have a new topology created over it once the
models form and possibly details have been sculpted. The new mesh will usually
have the original high resolution mesh information transferred into
displacement data or normal map data if for a game engine.
The modeling stage consists of shaping individual objects that
are later used in the scene. There are a number of modeling techniques, including:
constructive solid
geometry
implicit surfaces
subdivision surfaces
Modeling can be performed by means of a dedicated program (e.g.,
Cinema 4D, form Z, Maya, 3DS Max, Blender, Lightwave, Modo, solidThinking) or
an application component (Shaper, Lofter in 3DS Max) or some scene description
language (as in POV-Ray). In some cases, there is no strict distinction between
these phases; in such cases modeling is just part of the scene creation process
(this is the case, for example, with Caligari trueSpace and Realsoft 3D).
Complex materials such as blowing sand, clouds, and liquid
sprays are modeled with particle systems, and are a mass of 3D coordinates
which have either points, polygons, texture splats, or sprites assigned to
them.
Compared to
2D methods
3D photorealistic effects are often achieved without wireframe
modeling and are sometimes indistinguishable in the final form. Some graphic
art software includes filters that can be applied to 2D vector graphics or 2D
raster graphics on transparent layers.
Advantages of wireframe 3D modeling over exclusively 2D methods
include:
Flexibility, ability to change angles or animate images with
quicker rendering of the changes;
Ease of rendering, automatic calculation and rendering
photorealistic effects rather than mentally visualizing or estimating;
Disadvantages compare to 2D photorealistic rendering may include
a software learning curve and difficulty achieving certain photorealistic
effects. Some photorealistic effects may be achieved with special rendering
filters included in the 3D modeling software. For the best of both worlds, some
artists use a combination of 3D modeling followed by editing the 2D
computer-rendered images from the 3D model.
3D model market
A large market for 3D models (as well as 3D-related content,
such as textures, scripts, etc.) still exists - either for individual models or
large collections. Online marketplaces for 3D content, such as TurboSquid,
The3DStudio, 3DExport, CreativeCrash, CGTrader, FlatPyramid, NoneCG,
CGPeopleNetwork, Design Connected and DAZ 3D, allow individual artists to sell
content that they have created. Often, the artists' goal is to get additional
value out of assets they have previously created for projects. By doing so,
artists can earn more money out of their old content, and companies can save
money by buying pre-made models instead of paying an employee to create one
from scratch. These marketplaces typically split the sale between themselves
and the artist that created the asset, artists get 40% to 95% of the sales
according the marketplace. In most cases, the artist retains ownership of the
3d model; the customer only buys the right to use and present the model. Some
artists sell their products directly in its own stores offering their products
at a lower price by not using intermediaries.
Over the last several years numerous marketplaces specialized in
3D printing models have emerged. Some of the 3D printing marketplaces are
combination of models sharing sites, with or without a built in e-com
capability. Some of those platforms also offer 3D printing services on demand,
software for model rendering and dynamic viewing of items, etc. Among the most
popular 3D printing file sharing platforms are Shapeways, Pinshape,
Thingiverse, 3DExport, CGTrader, Threeding and MyMiniFactory.
3D Printing
3D printing is a form of additive manufacturing technology where
a three dimensional object is created by laying down successive layers of
material.
In recent years, there has been an upsurge in the number of
companies offering personalised 3D printed models of objects that have been
scanned, rendered in three dimensions in computer software, and then printed to
the customer's requirements. As previously mentioned, 3D models can be
purchased from online marketplaces and printed by individuals or companies
using commercially available 3D printers, enabling the home-production of
objects such as spare parts, and even medical equipment.
Human models
The first widely available commercial application of human
virtual models appeared in 1998 on the Lands' End web site. The human virtual
models were created by the company My Virtual Mode Inc. and enabled users to
create a model of themselves and try on 3D clothing. There are several modern
programs that allow for the creation of virtual human models.
3D modeling is used in various industries like films, animation
and gaming, interior designing and architecture. They are also used in the
medical industry for the interactive representations of anatomy. A wide number
of 3D software are also used in constructing digital representation of
mechanical models or parts before they are actually manufactured. CAD/CAM
related software are used in such fields, and with these software, not only can
you construct the parts, but also assemble them, and observe their
functionality.
3D modelling is also used in the field of Industrial Design,
wherein products are 3D modeled before representing them to the clients. In
Media and Event industries, 3D modelling is used in Stage/Set Design.