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@example.com
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 ….
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)
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
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 • 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 • 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.) • 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