Computer Graphics Techniques and Applications

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# Computer Graphics Techniques and Applications - PowerPoint PPT Presentation

Computer Graphics Techniques and Applications. Chapter 2 - 3D Modelling with Polygons Dr Brett Stevens e-mail: [email protected] phone: 023 9284 5482 address: West Wing, Eldon Building notes: http://techfaculty.port.ac.uk/cgtap. Last Week. 2D Graphics – Bitmaps. y. z.

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### Computer Graphics Techniques and Applications

Chapter 2 - 3D Modelling with Polygons

Dr Brett Stevens

e-mail: [email protected]

phone: 023 9284 5482

notes: http://techfaculty.port.ac.uk/cgtap

Last Week
• 2D Graphics – Bitmaps

y

z

x

3D Coordinate Systems

3D is defined by its representation system, but it can be initialised in different ways.

Left Hand Coordinates Right Hand Coordinates

What does 3D Studio Max use?

3D Studio Max Interface

Defining Coordinate Systems

3DS Max uses a rotated right hand coordinate system.

However this can be defined in relation to the …

• World
• View
• Local
• Parent
• Screen
• Grid

Representation method

Polygon

Easy to transform.

Easy to render.

Curved surfaces must be approximated.

Not suited to irregular objects.

Doesn’t model volume

Octree

Suited to irregular objects.

Can easily swap model size for accuracy.

Models volume

Difficult to transform.

Difficult to render realistically.

CSG

Models accurately.

Models volume.

Easy to render.

Easy to transform.

Limited application but used in some games development environments

Spline

Models curved surfaces accurately from little data.

Easy to transform.

Difficult to render.

Doesn’t model volume.

Fractal

Huge detail from small model.

Limited application.

Defining 3D Objects.
Polygon modelling

(Assume the viewpoint is at 0,0,10).

Listing the vertices in a polygon, can represent an object, but it makes it difficult to edit the edges.

Polygon Meshes

Vertices  Edges  Faces  Objects

Geometric Primitives and their Attributes

Primitives include, box, sphere, cylinder, pyramid and Teapot (amongst others).

Attributes include position, size and orientation, as well as object name and default colour.

Possible to add or subtract multiple primitives together to get new objects.

Affine Polygon Transforms
• Three basic transforms
• Translation (Change in position)
• Rotation (Change in orientation)
• Scale (Change in dimensions)

All done with matrix mathematics..!!!

Polygon Modifiers

Modifiers not transforms.

• Theses are found on the modifiers panel.
• e.g. Bend, taper, twist.

These do not preserve parallel lines.

Vertex / Edge/ Polygon Editing

Sub-object editing can be incredibly complex but it is a skill that improves with practice.!!!!

Requires conversion to a vertex representation (Editable Mesh).

Low poly Modelling

or

Sub-Division Surface Modelling (Sub-D)

Edit a simple object, and smooth the edges to make it look more realistic / organic.