3D file formats are used to store 3D model information such as geometry, appearance, scene, and animations. Common 3D file formats include STL, OBJ, FBX, COLLADA, 3DS, IGES, STEP, and X3D. STL is one of the most important neutral formats and encodes surface geometry using triangular meshes. OBJ also supports surface geometry encoding and stores appearance separately. FBX supports geometry, appearance, and skeletal animations. COLLADA supports geometry, appearance properties, animation, and physics.

1. 3D File Formats

2. What is 3D File Format
File that used to store information of about 3D
Models in format of plain text or binary data. Like
Geometry, appearance, scene and animations.

3. Element of 3D Model
• Geometry : It defines shape of model.
• Appearance: It includes colors, textures,
material etc.
• Scene: It defines position of light sources,
cameras and peripheral objects.
• Animation: It defines how 3D Model can move.

4. Geometry
• It is most basic feature of 3D File. Every model has unique
geometry and capability of encoding this geometry.
• Types of Geometry
1. Approximate Mesh
• 3D Model is covered with mesh of imaginary
polygons and triangles. The vertices of covering
triangles are stored in file.
2. Precise Mesh
1. Surface are made up of small number of weighted
control points and set of knots. (Knots are surface
that smoothly interpolating over control points).
3. Constructive Solid Geometry
1. It uses primitive shapes like cubes, spheres tp
create shapes.

5. Appearance
Appearance describes surface properties like material type,
texture, color etc.
Appearance can be encoded in two ways
1. Texture Mapping
• Every point in 3D Model’s surface is mapped into 2D image
and 2D Image coordinates have attributes like texture, color
etc. Rendering 3D Model, every surface point is assigned a
coordinate in 2D Image.
2. Face Attributes
• It stores texture information by assigning each face of mesh
attributes. Surface can have specular component indicating
the color and intensity of true mirror reflections of light
sources and other near surfaces. This component is encoded
by transmissive component describing color and intensity of
light that passing through surface.

6. Scene Information
• The scene describes layout of 3D Model in terms of
cameras, light sources and other 3D Model.
• Camera is defined by four parameters: magnification,
principal point, location, direction.
• Light source means nature of light like location, color
and intensity of it.
• Storing other nearby 3D Model is required when
model is consist of different parts and needs to
certain way to make up the scene.

7. Animation
Animation defines how 3D Model can move.
3D Animating ways
1. Skeletal Animation
1. Each model is associated with underlying skeleton. The
skeleton is made out of hierarchy of virtual “bones”. Movement
of bones higher in the hierarchy affect the bones lower in
hierarchy. Like Human body. Bones are connected by “joints”.
Joints defines constraints in the possible transformations for
bones, to restricting how bone can move in relation to its
parent.
2. Techniques of Animation
1. To store animations of skeletal structures, different techniques
can be used. E.g. forward kinematics, inverse kinematics,
keyframes etc.

8. File Types
• STL
• OBJ
• FBX
• COLLADA
• 3DS
• IGES
• STEP
• X3D

9. STL (STereoLithography)
• STL is one of most important neutral 3D file formats.
• One of oldest 3D file format.
• STL encodes surface geometry of 3D model using
triangular mesh.
• STL specifies both ASCII and binary representation.
• It ignores appearance, scene and animations.
• Used in 3D Printing, computer-aided manufacturing.

10. OBJ
• It is another neutral format.
• Mostly used in 3D Printing (full color) and 3D
Graphics.
• OBJ file format supports both approximate and
precise encoding of surface geometry.
• While using precise encoding, smooth curves and
surfaces used.
• Model appearance stored in different
file .MTL(material template library).
It does not support any kind of animation.
• Specifies both ASCII and binary encoding.

11. FBX
• It is proprietary file format. Used in AutoDesk
softwares like 3DS Max, Maya.
• Widely used in film industry and video games.
• It supports geometry and appearance.
It also provides skeletal animations and morphs.
• Both binary and ASCII files supported.

12. COLLADA
• It is neutral file format. (.DAE)
• Used in video game and film industry.
• Supports geometry, appearance related properties like
color, material, textures and animation.
It supports kinematics and physics.
• It stores data using XML.

13. 3DS
• 3DS file format using architecture, engineering,
education and manufacturing.
• This format retains only basic information about
geometry, appearance, scene and animation.
Uses triangular mesh to encode the surface geometry.
Limit for triangles is 65536.
• It doesn’t support directional light sources.
• Specifies in binary encoding.
• It is standard storing format for 3D Models and
interchanging between other 3D file formats.

14. IGES
• IGES is neutral file format.(.IGS, .IGES)
• Mostly used in defence industry (US Air Force) and
engineering field.
• It described in ASCII encoding.
• It is flexible for surface geometry.
• It stores color but doesn’t support properties like
textures, material types.
• Animation is not supported.

15. STEP
• Standard for the exchange for product data or ISO
10303. (.STP)
It is widely used in engineering related fields like
automative and aeronautic engineering, building
construction etc.
• Used to describing product data throughout life cycle
of product, independent from any system.
• It supports feature like surface geometry, storing color.
It supports additional encode topology, geometrical
tolerances, material properties like textures, materials
types and other product data.

16. VRML and X3D
• Virtual reality model language.
• Used in Internet and Web.
• Is uses polygonal mesh to encode surface geometry
with NURBS encoding.
Stores appearance related information like color,
texture, transparency.
• It has capability of storing scene related information
and support for animation.
Integrated with HTML5.