2.3. Graphics
The graphic data type means a data type that is constructed by a program.
The basic data type is a collection of besic building blocks. 3D CAD designs
are typical graphic data types. The basic construct is not an image, but
representation of a 3D object, a car, machine, mold. When the construct
is drawn on the screen "rendered", it becomes an image on the screen utilizing
the properties of image data type.
Media Type Graphic
Representation
Geometric Models
The basic building blocks of graphics. point, line, rectangle, polygon,
curve, coordinate system, structural hierarchies. The basic blocks can
be connected into structures, that can be duplicated and transformed.
Standards
-
GKS (Graphical
Kernel System)
-
PHIGS (Programmer's
Hierarchical Interactive Graphic System)
-
OpenGL (portable
system (Silicon Graphics))
Solid Models
Constructiong solids from the basic blocks
Constructive solid geometry (CSG)
(Set operations between solids)
Surface revolution. (A solid can be constructed by rotating a 2D object
about an axis = Lathing)
Extrusion (A 2D object is moved in 3D along a path)
Virtual
reality models (long document)
Physically based Models
Connecting physical properties in a model (mass, velocity, density,..)
Empirical Models
Probabilistic and particle systems used in constructing realistic effects.
Drawing Models
LOGO
External formats for Models
The presentation can be completed by set of formats expressing how to represent
the objects
CGM (Computer
Graphics Metafile)
Operations
Primitive editing
Changing the primitive components (points, lines,...)
Structural editing
Creating and modifying object collections and establishing spatial relationships.
Shading
Calculating the color on a surface. Model needed for the light source and
the surface qualities (reflection, diffusion)
-
Flat shading
-
Gouraud Shading.
-
Phong shading
-
Ray tracing (follow the path of a light ray from light source to the surface)
Mapping
-
Texture mapping ( spreading the texture on a surface)
-
Bump mapping (producing minor changes in the surface to make it more realistic)
-
Displacement mapping (local modifications to surface - moving parts of
the surface)
-
Environment mapping (simulate reflection)
-
Shadow mapping
Lighting
Simulating different forms of lightning (direction, color) on a model surface
-
Ambient light (backgroung light)
-
Point Light
-
Directional light
-
Spot light
Viewing
Sewlecting the location where the object is viewed. Projection - distance.
Rendering
Converting the object model in an image on screen or on paper.
mj@uwasa.fi 24.2.1997