CREATING A 3D IMAGEMichael Heron

INTRODUCTION

In this lecture we are going to look at the process we go through in order to build a 3D image. At least in theory. Will need to wait until the lab before we do it For

Reals. Two main techniques for doing this.

Line Mode Box Mode

TERMINOLOGY

Face A simple shape used to make up a more complex

shape. Also known as a polygon

Vertex A corner point of a polygon

Edge A line represented by two connected vertexes

CREATING A 3D OBJECT

We need to do several things. Define the geometry of the shape. Apply transforms to set

Location Scale Rotation

Define surface details. Textures

We do this for each object in a scene. We’ll talk about only one.

DEFINE THE GEOMETRY

How do we define the geometry? We choose between two main ways.

Or a hybrid of the two.

First way is to draw each point in the shape. For large, complex shapes – extremely difficult. The more polygons we have, the more difficult

this becomes. This is the line mode of drawing shapes.

There be dragons.

DEFINE THE GEOMETRY

How do you sculpt an elephant? You take a block of marble, and chip away all the

bits that don’t look like an elephant. This is the Box Mode of drawing shapes.

Start with an approximate shape. Usually one of the standard geometric principles.

Manipulate it until it fits your needs. Or at least, closely approximates your needs.

Recommended approach.

DEFINE THE GEOMETRY

A third way is to make use of a representation of a real object. Requires the use of specialised hard-ware

Which you don’t have.

The method you choose depends on The nature of the object Requirements of the model.

A hybrid approach is usually the best Start with a rough shape, draw extensions to

handle fine detail work.

3D REPRESENTATIONAL FORMS

Several ways to represent 3D Geometry: Polygonal.

Objects approximated by nets of polygons A polymesh

Bicubic Objects represented by nets of curved patches.

Constructive Solid Geometry Constructed from sets of basic geometric shapes

Space subdivision Ray-tracing

We focus primarily on polygonal today. Talk about the rest in the next lecture, or

thereabouts.

SIMPLE POLYMESH

(x1,y1,z1) (x2,y2,z2)

(x3,y3,z3)(x4,y4,z4)

(x5,y5,z5) (x6,y6,z6)

(x7,y7,z7)(x8,y8,z8)

SIMPLE POLYMESH – LOCAL CO-ORDINATES

(0,0,0) (50,0,0)

(50,0,50)(0,0,50)

(0,50,0) (50,50,0)

(50,50,50)

SIMPLE POLYMESH - REPRESENTATION

object surfaces polygons vertices

SIMPLE POLYMESH - REPRESENTATION

Represented by a face-vertex mesh A list of faces represented by vertexes A list of the vertexes and what faces they are

part of Co-ordinate space of each vertex.

This provides a mathematical, context independent representation of an object in its own local space.

FACE-VERTEX MESH

POLYMESH NOTES

Shape is only an approximation for complex images. Can’t represent a circle.

Can represent something that is almost a circle Level of approximation dictated by polygon

count. Shading and other detailing approaches can

help to hide shape approximations. Ubiquitous representation.

Graphics cards usually include specialised hardware for rendering large numbers of polygons.

DRAWING AN OBJECT

Begin with simple starting shape. Want to draw a head? Start with a sphere.

Can add a sphere as a base shape in Blender

Consider necessary transforms. Can do vertex, edge, and face manipulation

on polymesh shapes. Can apply basic transforms to part of a shape.

Can also extrude. Used to extend a part of a shape.

DRAWING AN OBJECT

Can also spin basic shapes:

http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Modelling_a_Mug_using_Spinning_and_Extrusion

DRAWING A SHAPE

Blender provides many different modifiers to change the basic structure of how you interact with a shape. Mirror allows you to mirror modifications across a

shape. Subsurf makes a rough image much smoother

and more organic. Lots of these modifiers

Experimentation is the key

MODIFIER - SUBSURF

MOLDING A SHAPE

Back to the elephant. How do we turn a simple shape into what we

actually want? Begin with a sphere

Elephant body Select appropriate faces on that sphere.

Extrude into legs Add another sphere

The head Extrude a trunk Extrude a tail

The rough work is handled using these kind of processes.

EXTRUSION

Extrusion is one of the most powerful tools you have available in blender. Pick a face, and extend it outwards or inwards.

Used to raise and lower surfaces. Can be used to create entirely new surfaces. Used to create shapes where shapes did not

previously exist. For example, in the coffee cup.

EXTRUSION

TEXTURING

Once you have a basic shape you want to make use of, you can apply various textures to it. This changes the colour, and how it interacts

with light sources. A base blender scene has three elements.

A light source (by default, the sun) A camera A shape

TEXTURING

The texturing system in Blender is extremely rich. You can set how your object interacts with light You can set the specific kind of rendering to be

done You can choose transparency and type of

textures. Most of these will not be visible except in

preview until a scene is rendered.

TEXTURES

Importantly, we can also make use of predefined bitmaps for a texture. We can make use of our own images which get

layered onto the shapes we provide. We’ll see more of this later lectures and labs.

It’s not a simple concept and easier to understand when shown rather than simply described.

Experimentation very important. Can’t even begin to cover what Blender makes

available!

SUMMARY

Polymeshes are the graphical representation must used. We’ll talk about the rest later.

3D Object created by: Representing geometry Applying transforms Applying textures Rendering