CSG
and Boolean set operations:
Sausage = bent cylinder plus spherical end-caps.
Show 2D composite.
B-rep
and winged-edge data structure:
Tessallate surface; describe polygons via vertices, edges.
Procedural modeling:
Sweep a circle through space along a curve. Start small for front-cap,
keep constant through main part of sausage, taper down to zero for end
cap.
("Procedural Generation of Parameterized Parts" -- NOT "Primitive Instancing"
!)
Instantiation
Hierarchy:
Ways to build complicated scenes in an organized manner.
Reuse parts that we have built several time, by making copies of them.
Hierarchical Scene Composition and
Description
Example #1: Houses on Hill
Example #2: Robot
World Space:
Hierarchy of groups and objects.
Rendering Space, Eye Space, Camera Space:
Defines from where do we view scene, what is ignored.
Form a new coordinate system with origin in eye (or camera lens), z-axis
in looking direction
The projection screen (retina, film) is perpendicular to that direction,
lies at some distance.
From eye we do a point (perspective) or parallel projection onto screen,
possibly clipping stuff that is too close or too far away.
Image Space:
This is the 2D space of the projection screen.
Often the scene hierarchy has been lost, just flat set of lines, polygons,
etc.
The drawing primitives may have been (re-)arranged into (display) segments;
these are grouping for similar treatment (color, transparency, visibility,
spatial location).
This set may be clipped by the Window = rectangular area defined in
projection plane.
Normalized Device Coordinates:
Fit everything into a unit square for easy manipulation and mapping
onto screen or into viewports
(=`window' to the laymen) on the screen.
This is achieved through a simple coordinate transformation of all
elements inside clipping window.
This gives us device independence !
Screen Space:
Pixels or x,y addresses of actual display device.
Dots, lines, filled areas, etc ... are expressed typically in integers
> 0.
Y-axis may be upside down.
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