A Summary of Modelling Lecture 9 (Modelling)

Modelling Techniques lConstructors:  Parametric and subdivision surfaces, CSG, blobby objects, surfaces of rotation, generalized cylinders, volumetric objects. lModifiers:  Spatial deformation lEvaluation:  Versatility (variety of achievable shapes)  Usability (how easy is it to understand controls and specify shapes)  Suitability for rendering and animation  Space Consumption lBeyond the Ivory Tower

Versatility lRepresenting Complex Shapes:  Creases: is it possible to introduce creases and corners. These can be either infinitely or semi sharp.  Smoothness: can continuity be guaranteed where required.  Varied Topology: are complex topologies (with a variety of holes) possible. CreasesContinuityTopology Parametric surfaces  Subdivision surfaces ? CSG  Blobby Objects  Generalized Cylinders  Volumetric Objects  Spatial Deformation 

Usability lSome desirable ease-of-use properties in modelling (c.f. usability course):  Closeness of mapping (between problem and solution)  Simplicity (“make things as simple as possible but no simpler).  Consistency (similar operations are expressed in a similar way).  Flexibility (technique does not require experience but rewards it)  Interactive Feedback (shape updates and display is immediate)  Fluidity (easy to make modelling changes)  Reversibility (undo changes)  Order Independence (can design operations be done in any order)  Direct manipulation (there is no indirection in control of the shape). lMore properties of the modelling system than the underlying techniques. lHowever: CSG, blobby objects and generalized cylinders are relatively intuitive (hide mathematical underpinnings).

Suitability for Rendering and Animation lRendering:  Polygon scan conversion requires that all representations be converted to a polygon mesh.  Ray tracing requires ray-object intersection tests. lAnimation:  Requires controls which allow the shape to vary over time. lBest Match:  Ray Tracing: CSG.  Polygon Scan Conversion: parametric and subdivision surfaces and generalized cylinders.  Animation: blobby objects, spatial deformation. lSpace Economy:  Most representations are compact (before conversion to Polygon Mesh) except volumetric objects.

Beyond the Ivory Tower lCAD/CAM:  Parametric surfaces and Constructive Solid Geometry. lVisualization:  Volumetric techniques for Biomedical applications. lSimulation, 3D Games:  Any technique amenable to pre-processed conversion to polygon- mesh and which produces low polygon counts.  Often use decimation techniques to reduce number of polygons. lFilm:  Almost all techniques (subdivision surfaces - “Geri’s Game”, “Toy Story 2”, blobby objects - “Flubber”).  But, often model objects in clay and then laser scan directly to polygon mesh (“Star Wars: Episode I”, “Godzilla”).

Course Structure and Evaluation

Course Timetable 25 AprilVideo: “Story of Computer Graphics” 30 AprilAnimation 1: Dynamics and Kinematics. 2 MayAnimation 2: Traditional Hand Animation, Motion Capture and Summary. 4 May S. Nirenstein, Phd Student: “Visibility Culling”. 7 MayR. Southern, MSc Student: “Multiresolution Methods”. 9 MaySeminar 1 11 MaySeminar 2 15 MaySeminar 3 16 MaySeminar 4 18 MaySeminar 5

Course Evaluation lSeminar (25%):  A 30-minute presentation on a sub-topic of advanced computer graphics.  Developing demonstration software to illustrate an aspect of the topic is encouraged.  Presented in teams of two. Presentation must be shared equally between team members. lMini Research Report (25%):  A technical document written in article style (with abstract and references) on the same topic as the seminar.  Marks will be allocated for technical writing competency.  Due 25 May. lExamination (50%):  A conventional written examination (not open book).

Seminar Structure lPresentation by student group (30 minutes)  Each speaker talks for roughly 15 min each. Topic is covered in detail with relevant examples and demonstrations. lQuestions and paper discussion (15 minutes)  The speakers select a key paper in their topic and distribute copies (or a link to pdf) to all students at the previous lecture.  Students must read the paper in the interim and be prepared to discuss its contents, especially strengths and weaknesses.

Seminar Topics 1.Select a sub-topic from the Advanced Computer Graphics course notes that was not covered in detail. Examples include: a.Pen and Ink Rendering b.Advanced Illumination Methods c.Subdivision Surfaces d.Quaternions e.Progressive Meshes 2.Browse through the SIGGRAPH 2000 proceedings and pick a paper that you think is interesting. Then research the background.