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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