1. CSc 8820 Advanced Graphics Algorithms
Ying Zhu
Georgia State University
Lecture 19
Overview of 3D Modeling

2. Outline The 3D computer graphics process The 3D modeling techniques
Surface models
Polygon mesh models
Subdivision surfaces
Parametric curves and curved surfaces
Solid models
Procedural models

3. The 3D computer graphics process for movies
The modelers create 3D models using modeling tools
The animators create animations using animation tools
Eventually create frame-by-frame animation
The animation sequence is sent to the rendering software for rendering, one frame of an image at a time
The images are saved into one or more video files
Post-production, video editing, etc.

4. The 3D computer graphics process for games
The modelers create 3D models
3D models are saved in model files
Animators create animation sequences for each 3D object
Saved in a library of motion sequences
Programmers write game programs that load and display the 3D models and animation sequences based on current game play
Game engine and game AI determines which model and which animation sequence to load

5. What is 3D modeling? 3D modeling may include several activities
Edit the shape of individual objects
Edit the object surface material properties
Apply textures (texture mapping)
Apply bump-maps
Prepare a 3D model for animation
E.g. fit an object with a skeleton for later animation
Overall, 3D modeling is the process of creating a scene

6. How to do it? Use 3D scanning Use modeling and animation tools
E.g. Blender, 3DS Max, Maya, etc.
Use scene description language
E.g. POV-Ray
Use 3D graphics API (E.g. OpenGL, DirectX, etc.)
Procedural modeling
Reconstruct 3D objects from a set images

7. Hybrid approach Get a real object or create a miniature object
Scan the real object or the miniature object to obtain a 3D digital model
Use modeling tools to edit and refine the 3D digital model

8. 3D scanner Head and face scanner
Motion range: 0 – 360 degrees (cylindrical), 0 – 350mm (Y stage travel)
Applications: sculpture, VR, animation, medicine, etc.
Output file format: 3D Studio, PLY, OBJ, ASCII, etc.
Image courtesy
of Cyberware

9. How does 3D scanning work?
Multiple profiles are captured and positioned in 3D space each second, resulting in a high accuracy high density 3D point cloud.
This 3D point data can processed to become a polygon mesh
Images courtesy of 3dscanner.com

10. Surface reconstruction case study
The Digital Michelangelo Project.
30 faculty, staff, and students from Stanford University and the University of Washington spent the academic year in Italy scanning the sculptures and architecture of Michelangelo.
The motivations are to advance the technology of 3D scanning, to place this technology in the service of the humanities, and to create a long-term digital archive of some important cultural artifacts.
More information at:

11. The Digital Michelangelo Project
The largest dataset was of the David – 2 billion polygons and 7,000 color images.
For each statue and map fragment, researchers must
clean up the raw scans
align them with each other
merge them to form a seamless mesh
fill holes in this mesh
map color photographic data onto it.
Perhaps the biggest surface reconstruction project in history

12. Models from 3D scanning The Stanford 3D scanning repository
GA Tech large geometric models archive

13. Polygon Mesh Models
The polygon mesh data structure is the most common and oldest modeling method for computer graphics.
"Perspective Study of a Chalice", by Paolo Uccelloin , Florence, Italy

14. Polygon Mesh Method
A mesh is a collection of vertices and polygons that define the shape of an object
Meshes usually contain only triangles because it's easier to deal with triangles than general polygons
Benefits
Creating complex objects is simple. There are no limits to what a polygon mesh surface can do.
Drawbacks
Need to store large numbers of points in order to get a smooth surface. 
Also, if you want to animate that surface, you have to determine a transformation for each of those points. 

15. Issues with polygon mesh model
Model complexity vs. rendering speed
You need more and smaller polygons to model fine details of an object
But the more polygons you have in a scene, the slower the rendering
There is usually an upper limit (called polygon budget) for the number of polygons per scene
Especially for real-time graphics applications that requires 30+ frame/sec frame rate

16. Subdivision surfaces
The process of taking a low resolution polygon mesh and refining it to produce another shape that is more visually attractive (usually smooth)
Subdivision Surfaces are defined by an initial polygonal mesh, along with a subdivision (or refinement) operation.
Given a polygonal mesh, subdivision algorithm will generate a new mesh that has a greater number of polygonal elements, and is smoother

17. Subdivision surfaces

18. Parametric curves and surfaces
Use mathematical formulations to describe curves and surfaces
E.g. a NURBS surface

19. Solid modeling
Solid modeling describes the volume of space occupied by a solid
Necessary for many applications where objects must be maintained as solids.
Finite element analysis
CAD/CAM
Mass property determination
Every solid is defined and stored by its boundary, consists of faces, and includes the topology for each face

20. Procedural modeling
Some irregular or complex objects have dynamic topologies
Some objects have no solid surface
E.g. Smoke, water, etc.
Usually we need to write programs to generate these objects
E.g. particle systems, fractals, and L-systems

21. Modeling Natural Phenomena
Water (by Dr. Ron Fedkiw, et al.)

22. Fire
Fire

23. Smoke
Smoke

24. Cloud Cloud (by Dr. David Ebert)

25. Plants and Flowers
Plants and flowers (by Dr. Przemyslaw Prusinkiewicz, et al.)

26. Terrain Fractal method for terrain modeling (by Dr. Ken Musgrave)

27. Summary The 3D computer graphics process The 3D modeling techniques
Surface models
Polygon mesh models
Subdivision surfaces
Parametric curves and curved surfaces
Solid models
Procedural models

28. Reference Download and try Blender The Digital Michelangelo Project
Download and try Blender