adaptively sampled distance fields: a general representation of shape for computer graphics sarah f....
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Adaptively Sampled Distance Fields:A General Representation of Shape for Computer Graphics
Sarah F. Frisken, Ronald N. Perry, Alyn P. Rockwood, and Thouis R. JonesMERL – Mitsubishi Electric Research Laboratory
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Distance Fields
• A distance field is a scalar field that – specifies the minimum distance to a shape ...– where the distance may be signed to distinguish between
the inside and outside of the shape
• Distance is not restricted to Euclidean
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2D Euclidean Distance Field Example
R shape Distance field of R
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2D Euclidean Distance Field Example
3D visualization of distance field of R
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Shape
• By shape we mean more than just the 3D geometry of physical objects. Shape can have arbitrary dimension and be derived from simulated or measured data.
Color gamut
Color printer
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Advantages for Shape Representation
• Represent more than the surface– object interior and the space in which the shape sits
• Gains in efficiency and quality because – distance fields vary “smoothly”– are defined throughout space
• Gradient of the distance field yields– surface normal for points on the surface– direction to closest surface point for points off the
surface
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Advantages for Shape Representation
• Smooth surface reconstruction• Inside/outside and proximity testing• Boolean operations• Surface offsetting• Geometric queries such as closest point• Numerous applications
– blending and filleting– morphing– rough cutting– collision detection– path planning
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Sampled Distance Fields
• Similar to sampled images, insufficient sampling of distance fields results in aliasing
• Because fine detail requires dense sampling, excessive memory is required with regularly sampled distance fields when any fine detail is present
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Adaptively Sampled Distance Fields (ADFs)
• Detail-directed sampling– high sampling rates only where needed
• Spatial data structure– fast localization for efficient processing
• ADFs consist of – adaptively sampled distance values …– organized in a spatial data structure …– with a method for reconstructing the distance field
from sampled distance values
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Various ADF Representations
• Spatial data structures– octrees– wavelets– multi-resolution tetrahedral meshes ...
• Reconstruction functions– trilinear– B-spline wavelet synthesis– barycentric ...
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Examples of 2D Spatial Data Structures Quadtree
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Examples of 2D Spatial Data Structures Wavelet
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Examples of 2D Spatial Data Structures Multi-resolution Triangulation
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Related Work
Volume sculptingAvila and Sobierajski, 1996Baerentzen, 1998Galyean and Hughes, 1991Wang and Kaufman, 1994
Multi-resolution volumesCignoni, De Floriani, Montani, Puppo and Scopigno, 1994Hamann and Cehn, 1994Ertl, Westerman and Grosso, 1998Westermann, Sommer and Ertl, 1999
Implicit surfacesBloomenthal, 1997Desbrun and Gascuel, 1995Larcombe, 1994Gascuel, 1998Ricci, 1973
Distance fieldsBarerentzen, Sramek and Christensen, 2000Breen, Mauch and Whitaker, 1998Cohen-Or, Levin and Solomovici, 1997Curlass and Levoy, 1996Gibson, 1998Kimmel, Kiryati and Bruckstein, 1998Lengyel and Reichert, 1990Payne and Toga, 1992Schroeder, Lorensen and Linthicum, 1994Yagel, Lu, Rubello and Miller, 1995Zuiderveld, Koning and Viergever, 1992
Level setsOsher and Sethian, 1988 Sethian, 1996Whitaker and Breen, 1998
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A Gallery of Examples - A Carved Vase
Illustrates smooth surface reconstruction, fine carving, and representation of algebraic
complexity
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A Gallery of Examples - A Carved Slab
Illustrates sharp corners and precise cuts
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A Gallery of Examples - A Volume Rendered Molecule
Illustrates volume rendering of ADFs, semi-transparency, thick surfaces, and distance-based turbulence
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A Gallery of Examples - The Menger Sponge
ADFs simplify the data structures neededto represent complex objects
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ADFs - A Unifying Data Stucture
• Represents surfaces, volumes and implicit functions
• Represents sharp edges, organic surfaces, thin-membranes and semi-transparent substances
• Consolidates multiple structures for complex objects
• Can store auxiliary data in cells or at cell vertices
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An Example - Octree-based ADFs
• Store distance values at cell vertices of an octree
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Reconstruction
• Distances and gradients are estimated using trilinear reconstruction
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Reconstruction
A single trilinear field can represent highly curved surfaces
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Bottom-up Generation
Fully populate Recursively coalesce
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Top-down Generation
Recursively subdivideInitialize root cell
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Surface Exclusion
(1) all di have same sign(2) all || di || > ½ cell diagonal
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Predicate Test for Subdividing and Coalescing Cells
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Comparison of 3-color Quadtrees and ADFs
23,573 cells (3-color) 1713 cells (ADF)
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Editing with Boolean Operations - Local ADF Regeneration
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2D Editing with Boolean Difference Operator
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Rendering
• Surface rendering– ray casting with analytic surface intersection
• Volume rendering– back-to-front sampled ray casting
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Surface Rendering - Cubic Solver
• See Parker, et al.
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Surface Rendering - Linear Solver
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Crackless Surface Rendering with the Linear Solver
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Volume Rendering
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Applications
“It’s a shirt. It’s a sock. It’s a glove. It’s a hat. But it has other uses. Yes, far beyond that. You can use it for carpets. For pillows! For sheets! Or curtains! Or covers for bicycle seats!”
— The Lorax, Dr. Seuss
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Applications - Carving
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Applications - Carving
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Applications - Level of Detail
• Different ways to compute LOD from an ADF– octree level cut-off– stored error cut-off
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Other Application Areas
• Collision detection• Color gamut representation• Milling• Path planning• Volumetric effects
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Conclusions
• ADFs are a unifying representation of shape• They integrate numerous concepts in
computer graphics including – the representation of geometry and volume data– a broad range of processing operations such as
rendering, carving, LOD management, surface offsetting, and proximity testing