1. Spring 2006 G5BAGR – Advanced Computer Graphics
Guoping Qiu
Lecture note from Dr Bai Li

2. Methods & Resources
Lectures: Wednesday 12: :00 NEW-A24 Thursday 9:00 -10:00 NEW-A26
Assessment: 100% exam
Learning materials:
Books:
Computer Graphics: principles and practice (3rd edition), by Foley et al.
Interactive Computer Graphics: A Top-Down Approach with OpenGL, by Edward Angel.
Any other appropriate CG books, Journals, Articles ….
Online notes
Lab Facility: OpenGL Library

3. Contents
3D graphics - creating 3D scenes and viewing them as 2D images
Module roughly follows the graphics pipeline, topics include
3D Modeling
Transformation
Viewing
Clipping
Projection
Hidden Surface Removal
Lighting Models
Texture Mapping
Curves & Surfaces
Other advanced topics in CG

4. 3D Graphics Pipeline Graphics pipeline involves
Creating objects/scene – 3D modeling
define objects in local coordinate system
transform library objects
transform objects to world coordinate system
Determining which part of the objects/scene are visible
Camera model (position, direction, focal length) to define viewing volume
Transform objects to camera coordinate system
Clipping against view volume to determine visible objects
Projection to obtain 2D representation of objects
Determining which pixels should be filled
Rasterization – from vectors/polygons to pixels
Hidden Surface Removal - determine which object in the view volume should appear in image at each pixel
Determining what color/texture/lighting it is
Lighting models and texture mapping

5. Modelling Scene = list of objects Object = list of surfaces
Surface = list of polygons
Polygon = list of vertices
scene
vertices
object
surfaces
polygons 4

6. Polygon Data Structure

7. Polygon Mesh
Each polygon is planar. We need a large number of small polygons to give the impression of curved surfaces:
48 polygons
120 polygons
300 polygons
1000 polygons

8. Polygon Mesh

9. Polygon Mesh Creation Laser scanning Stereo matching Structured light
Software then takes thousands of points (point cloud) and builds a polygon mesh out of them
Research topics:
Reduce number of mesh points
Reconstruction

10. 3D Viewing

11. Viewing and Clipping camera world (viewing) coordinate coordinate
view frustum
camera setup
outside view so
must be clipped

12. View Volume (Frustum) back view frustum plane view window camera frontzV 16 16

13. Projection
camera setup
viewport
3d models

14. Rasterisation
Rasterisation, or scan conversion, is the process of finding which pixels an individual polygon covers or, at a more basic level, which pixels an edge of a polygon lies on
Generally polygons are filled using horizontal line segments; these can be thought of as the intersection of the polygon with a particular scan line.

15. Hidden Surface Removalz x y z2 z1 B A
There are two basic ways of ordering the rendering of a scene. These are:
On a polygon-by-polygon basis
The z-buffer approach
The z-buffer algorithm is equivalent to, for each pixel, a search through the associated z values of each interior polygon point to find the point which holds the minimum depth value z (nearest to the viewer).

16. 3d Modelling
Lighting Models
Texture Mapping
Curves and surfaces