Post on 18-Dec-2015
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Assignment
OrthographicWireframeElevation
OrthographicWireframe
Plan
OrthographicWireframeEnd-Elevation
PerspectiveView
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Assignment (cont…)
Your application must include the following:– Four different views of a scene:
• An orthographic wireframe elevation of the scene which does not change
• An orthographic wireframe plan of the scene which does not change
• An orthographic wireframe end-elevation of the scene which does not change
• A perspective view of the scene in which the user should be able to move the camera
– A scene composed of at least the following:• 1 teapot• Ten different objects• One animating object
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Assignment (cont…)
– At least one light source– At least one bitmap textured surface– Controls (using whatever modality you see fit,
e.g. keyboard, mouse etc) that allow a user to:
• Turn on and off the lights in the scene• Navigate around the perspective view of the
scene• Reset the view of the scene to the initial position
– A representation in each of the orthographic views of the camera position used in the 3-D perspective view
– Correct resizing of the window
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Assignment (cont…)
– JAZZ! A considerable portion of the marks (20%) for this assignment will be awarded for doing something interesting in the application beyond what is given as the minimum requirements. Examples might include:
• Using models designed in 3DS max/Milkshape/Maya
• Adding interesting effects such as particle systems
• Adding clever use of lighting – for example have the light source appear to be the lamp in the scene in figure 1
• Add a sky box
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Assignment (cont…)
Assignment submission deadline: 8th December, 2006
Submission of the assignment will be through WebCT
Any Questions?
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CGames
The 9th International Conference on Computer Games: AI, Animation, Mobile, Educational & Serious Games will be held at DIT from the 22nd – 24th of November
All DIT students are allowed attend all sessions free of charge – graphics labs/lectures will be rearranged to accommodate this – more to follow
For more: www.comp.dit.ie/cgames
Course Website: http://www.comp.dit.ie/bmacnamee
Computer Graphics 10:3D Object
Representations
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Contents
In today’s lecture we are going to start to look at how objects are modelled in 3D
– Polyhedra– Quadric surfaces– Sweep representations– Constructive solid geometry methods
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Polyhedra
Objects are simply a set of surface polygons that enclose an object interior
Simplest and fastest way to render objects
Often referred to as standard graphics objects
In many cases packages allow us to define objects as curved surfaces etc but actually convert these to polygon meshes for display
To define polyhedra we simply define the vertices of the polygons required
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Polyhedra (cont…)Im
ages
tak
en f
rom
Hea
rn &
Bak
er,
“Com
pute
r G
raph
ics
with
Ope
nGL”
(20
04)
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Quadric Surfaces
A frequently used class of objects are quadric surfaces
These are 3D surfaces described using quadratic equations
Quadric surfaces include:– Spheres– Ellipsoids– Tori– Paraboloids– Hyperboloids
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Quadric Surfaces - Spheres
A spherical surface with radius r centred on the origin is defined as the set of points (x, y, z) that satisfy the equation
This can also be done in parametric form using latitude and longitude angles
2222 rzyx
sin
sincos
coscos
rz
ry
rx
22
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Quadric Surfaces – Spheres (cont…)
y axis
z axis
x axis
P ( x, y, z )
θ
φ
r
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Sweep Representations
Sweep representations are useful for constructing 3 dimensional objects that possess translational, rotational or other symmetries
Objects are specified as a 2 dimensional shape and a sweep that moves that shape through a region of space
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Sweep Representations - ExamplesIm
ages
tak
en f
rom
Hea
rn &
Bak
er,
“Com
pute
r G
raph
ics
with
Ope
nGL”
(20
04)
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Constructive Solid Geometry Methods
Constructive Solid Geometry (CSG) performs solid modelling by generating a new object from two three dimensional objects using a set operation
Valid set operations include – Union– Intersection– Difference
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Constructive Solid Geometry Methods (cont…)
Imag
es t
aken
fro
m H
earn
& B
aker
, “C
ompu
ter
Gra
phic
s w
ith O
penG
L” (
2004
)
Difference
Intersection
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Constructive Solid Geometry Methods (cont…)
CSG usually starts with a small set of primitives such as blocks, pyramids, spheres and conesTwo objects re initially created and combined using some set operation to create a new objectThis object can then be combined with another primitive to make another new objectThis process continues until modelling complete
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Constructive Solid Geometry Methods (cont…)
CSG Object
oper1
obj1 obj2
oper3
obj4 oper2
obj2 obj3
CSG models are usually represented
as CSG trees
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Constructive Solid Geometry Methods (cont…)
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Ray-Casting
Ray-casting is typically used to implement CSG operators when objects are described with boundary representations
Ray casting is applied by determining the objects that are intersected by a set of parallel lines emanating from the xy plane along the z axis
The xy plane is referred to as the firing plane
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Ray-Casting (cont…)Im
ages
tak
en f
rom
Hea
rn &
Bak
er,
“Com
pute
r G
raph
ics
with
Ope
nGL”
(20
04)
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Ray-Casting (cont…)
Surface intersections along each ray are calculated and these are sorted according to distance from the firing plane
The surface limits for the composite object are then determined by the specified set operation
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Ray Casting ExampleIm
ages
tak
en f
rom
Hea
rn &
Bak
er,
“Com
pute
r G
raph
ics
with
Ope
nGL”
(20
04)
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Summary
In today’s lecture we began to look at how objects are modelled in 3DPolyhedra are by far the most common modelling technique, but there are many othersOften more exotic modelling techniques are used in a modelling phase, but the resultant models are converted to polyhedra before renderingNext time we will look at more modelling techniques