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N420 / D379 Multimedia Project Development Fall 2000 PowerPoint PPT Presentation

N420 / D379 Multimedia Project Development Fall 2000 Topic 4: 3D Geometric Graphics Dr. Jeffrey Huang, Assistant Professor The School of Informatics, New Media Program, IUPUI e-mail: [email protected] 3D Graphics 3D Computer Programs

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N420 d379 multimedia project development fall 2000 l.jpg

N420 / D379 Multimedia Project DevelopmentFall 2000

Topic 4:

3D Geometric Graphics

Dr. Jeffrey Huang, Assistant Professor

The School of Informatics, New Media Program, IUPUI

e-mail: [email protected]


3d graphics l.jpg

3D Graphics

  • 3D Computer Programs

    • Rapidly create, view, and change 3D forms without using physical 3D materials

    • Easily construct abstract 3D spaces – building and combining objects

    • Experimenting different “material properties”

      • Reflectiveness, transparency, and texture

      • Controlling lighting effects

    • Creating 3D models and looking at them from any point of view

    • Frustration:

      • Difficult to work with 3D information on a 2D screen with 2D input device

      • Unfamililiar technical terms: Primitives, polygonal meshes, sweeping a profile, Gouraud shading, ray tracing ….


Slide3 l.jpg

3D Concepts

  • Use all concepts and methods in 2D graphics

    • 2D geometry  2D shapes  continuous 2D geometric description  reaterized  raster-based screens and printers

    • 3D geometry 2D & 3D shapes  continuous 2D geometric description  reaterized  raster-based screens and printers

      • Challenges: added dimension and effects of lighting on object surfaces

  • Modeling

    • Create 3D objects (similar to 2D in digital design and layout program)

  • Rendering

    • Rasterize the models (more complex than in 2D)

      • Project 3D information onto a 2D plane for display

      • Calculate lighting effects on object surfaces (hardware acceleration)


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Modeling

  • Modeling is coping with complexity (van Dam, 1994)

    • Creating the objects, concept, or phenomenon that presents the important features

    • However, only presenting some part of a scene (feeling, experience, salient features), while leaving other parts out

    • 3D geometric modeling

      • Need not be based on physical geometric forms

      • Can be Scientific Visualization (data exploration) – creation of images based on very large sets of data. Ex: Wind Flow, NASA, …

  • Depth

    • X - and y - axes on Cartesian coordinate system + z -axis


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Modeling (cont.)

  • 3D geometric modeling

    • Create simple model elements

    • Assemble the elements into more complex objects

    • Arrange objects in a 3D scene

    • Choose materials

    • Set up lights

    • Choose view points and rendering model

  • Behavioral modeling

    • Model objects’ behaviors

    • Animate articulated characters, facial expression, realistic skin deformation. Ex: deformable model, particle system, …

  • Real 3D world accuracy


Rendering l.jpg

Rendering

  • Rendering

    • Rasterize the models

    • Project 3D onto 2D plane

    • Calculate lighting effects on object surface

  • Surface Properties

    • Complexity of color in 3D

      • Color picker is not quite helpful because 3D CG model almost never appears to be a single color

        • Gradients of color value

        • Reflection and shadow from surrounding objects and lights make color change

      • Surface normal

        • Outward-facing direction of the face

      • Vector

        • A line with direction (arrow)

  • normal


    Surface properties l.jpg

    Surface Properties

    • Surface reflection properties

      • Diffuse reflection

        • angle of the light shining on surface

        • Light bounces equally in all directions

      • Specular reflection

        • mirror-like reflection

        • highlights

        • Material dependent, view dependent

        • Light bounces off only at an angle equal and

          opposite to that of the incoming light

        • Non-perfect reflector: specular highlight is evident over a small angle and loses its coherence

      • Combination of diffuse and specular reflection: Diffuse + Specular

    Incoming light

    Diffuse

    Perfect specular

    Imperfect specular

    Diffuse + Specular


    Surface properties cont l.jpg

    Surface Properties (cont.)

    • Surface Transmission properties

      • Light is absorbed

      • Light is transmitted

        • Transparency: light is not reflected

        • Refracted light: when light passes through different media it is bent

      • Refraction index: water  1.3, air  1, diamond  2.4

    • Texture

      • 3D paint-type images applied to 3D objects

      • 3D painting


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