Download - A Search Engine for 3D
7/31/2019 A Search Engine for 3D
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Goal
Search engine for 3D models
Challenges
Simple query methods Robust shape matching methods
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A decade ago
Draw a picture
Copy a picture Photograph a picture
Today
Search from the web
3D model?
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Easy to construct
New scanners
Interactive tools Fast, inexpensive graphics hardware
Widespread distribution
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How do we construct them?
How do we find them?
A city sceneCars
Street lamps
Stop signs
Research in retrieval, matching, recognition,
classification
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Keywords?
Not annotated
Annotated with inspecific key wordsToo common
Not known
Shape-based query
Distinguish similar objects
A picture is worth a thousand words
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Shape descriptors
Spherical harmonics descriptors
User interfaces3D sketching
2D sketching
Text
Interactive refinement
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2D
hard to extend
Registration, recognition, matching
Time consuming
Local, sensitive
Statistical properties
Not discriminating enough Specific data types
CAD parts, protein molecules, cultural artifacts
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Indexed a large repository
Supported 2D and 3D sketching
Studied interaction between text and shape
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Crawling 17,834 VRML
2,873 commercial
Indexing
Descriptive
Concise
Efficient to compute
Robust to model degeneracy
invariant to rotations
Query
Text keywords
2D sketching
3D sketching
Model matching Iterative refinement
Matching
16 results
< 0.25 seconds
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Two types File name
Find similar shape
Desirable descriptor
Quick to compute Concise to store
Easy to index
Invariant under similarity transformations
Insensitive to noise and small extra features
Independent of 3D object representation, tessellation, or genus Robust to arbitrary topological degeneracies
Discriminating of shape differences at many scales
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Most high-level shape representations
Require a consistent model of the object’s
boundary and interior
Other shape representations Require a priori registration into a canonical
coordinate system
Statistical shape descriptors
Not discriminating enough
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Euclidean distance
K best matches: k nearest neighbours
Search in 1D space first
Compute true distance
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3D sketch
Teddy + matching
Hard to learn
Extrusion Cuts
Rotate
Blobby objects: genus zero
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2D sketch
Pixel paint + match 2D projections
Properties
Easy Less info: multiple projections
Challenge
Match 2D sketches to 3D objects
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Algorithm Computer matching score
Each pair of m sketches versus 13 2D views
Minimal sum of m pairwise sketch-to-thumbnail
scores
No thumbnail can be matched to >1 sketch
Advantages
Any sketched view is with 22.5o of a sample view
Some aligned with axes
Label side, front, and top
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Fourier Descriptors
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Representative document
Filename, web text, labels inside model file
Removing common words
Stem text Add synonyms
Matching tool: Bow toolkit
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Example 1First query: text
Second query: text + shape
Example 2
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Algorithm for finding K top matches
Find the best M matches for each mode
Mean-normalize them (mean 0, var 1)
Return K models with the highest averagenormalized scores
Currently K=16, M=128
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Query interfaces: text, 2D/3D sketches, 3D
models
New descriptor Shape + text = useful
A large repository of 3D models