There are three main ways to represent 3D models: polygonal modeling using vertices and faces, curve modeling using control points and surfaces, and digital sculpting which directly modifies polygon positions. Modeling programs allow creating 3D objects and include tools for constructive solid geometry, implicit surfaces, and subdivision surfaces. Popular commercial programs are 3ds Max, SketchUp, and LightWave, while Blender is a free and open-source option.

1. There are Three popular ways to represent a model:
1. 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.
2. 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
3. Digital sculpting - Still a fairly new method of modeling, 3D sculpting has become
very popular in the few short 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., 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.
http://en.wikipedia.org/wiki/3D_modeling

2. Autodesk 3ds Max, formerly 3D Studio Max, is 3D computer graphics software for making
3D animations, models, and images. It was developed and produced by Autodesk Media and
Entertainment. It has modeling capabilities, a flexible plugin architecture and can be used on
the Microsoft Windows platform. It is frequently used by video game developers, TV
commercial studios and architectural visualization studios. It is also used for movie effects
and movie pre-visualization.
In addition to its modeling and animation tools, the latest version of 3ds Max also features
shaders (such as ambient occlusion and subsurface scattering), dynamic simulation, particle
systems, radiosity, normal map creation and rendering, global illumination, a customizable
user interface, and its own scripting language.[1]
http://en.wikipedia.org/wiki/Autodesk_3ds_Max
SketchUp is a 3D modeling program optimized for a broad range of applications such as
architectural, civil, mechanical, film as well as video game design — and available in free as
well as 'professional' versions.
The program highlights its ease of use,[2] and an online repository of model assemblies (e.g.,
windows, doors, automobiles, entourage, etc.) known as 3D Warehouse enables designers to
locate, download, use and contribute free models. The program includes a drawing layout
functionality, allows surface rendering in variable "styles," accommodates third-party "plug-
in" programs enabling other capabilities (e.g., near photo realistic rendering) and enables
placement of its models within Google Earth.
In early 2012, Google, the previous owner of Sketchup, announced it will sell the program to
Trimble, a company formerly known for GPS location services
http://en.wikipedia.org/wiki/SketchUp
LightWave is a software package used for rendering 3D images, both animated and static. It
includes a rendering engine that supports such advanced features as realistic reflection and
refraction, radiosity, and caustics. The 3D modeling component supports both polygon
modeling and subdivision surfaces. The animation component has features such as reverse
and forward kinematics for character animation, particle systems and dynamics. Programmers

3. can expand LightWave's capabilities using an included SDK which offers LScript scripting (a
proprietary scripting language) and common C language interfaces.
Blender is a free and open-source 3D computer graphics software product used for creating
animated films, visual effects, interactive 3D applications or video games. Blender's features
include 3D modeling, UV unwrapping, texturing, rigging and skinning, fluid and smoke
simulation, particle simulation, animating,match moving, camera tracking, rendering, video
editing and compositing. It also features a built-in game engine.
http://en.wikipedia.org/wiki/Blender_(software)