A Photograph of two papers
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Transcript of A Photograph of two papers
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A Photograph of two papers
• The Model: 2 papers– 8cm x 8cm and 5cm x 5cm
• The Camera– Simple pinhole – No focusing capability
• The Scene– Arrangements model
and camera– Light sources (later)
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The Arrangements
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3D Coordinate Systems
• Two options for Z-axis direction!– Same position, different sign for z-value!!
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Left vs. Right Handed Systems
• Right-Handed System EXCLUSIVELY!!
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The Model and the Scene
• Right-Handed Coordinate System• Convenience– Origin
Center of 8x8– Units
in cm
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Details …
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A Computer Graphics Camera
• Camera position• Look at position• Up direction• Related terms:
– Image Plane– Viewing Direction– View Vector
• Maya scene
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The Up Direction (Up Vector):
• Also referred to as: Twist Angle– Cannot be parallel to viewing direction– Does not need to be normalized– Does not need to be perpendicular to
viewing direction
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Controlling the Up Vector
• z=slider:
• Twist angle:
• not perpendicularto View Vector!
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The Visible Volume
• Only geometries (primitives) inside the volume are visible
• All geometries (primitives) outside are ignored• Primitives straddle the volume are Clipped!
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The Rectangular Visible Volume
• Volume defined by:– Near Plane (n)– Far Plane (f)– Width (W)– Height (H)
• For Orthographic Projection
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Orthographic Projection
• Maya Scene
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The Viewing Frustum Volume
• Volume defined by:– Near Plane (n)– Far Plane (f)– Fields of view (fov)
• For Perspective Projection
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Near Plane and Aspect Ratio
• Aspect Ratio
• Near Plane– Height (nh)
– Width (nw)
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Perspective Projection
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• Orthographic Projection– Parallel projection– Preserve size• Good for determining relative size
• Perspective Projection– Projection along rays– Closer objects appears larger– Human vision!
• Only work with: Perspective Projection
Orthographic vs Perspective Projection