Freehand%20Drawing%20System%20based%20on%20Geometric%20Constraints

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Freehand Drawing Systembased on Geometric
Constraints

• Kaisuke Nakajima
• Joint work with Takeo Igarashi

User Interface Research Group The University of
Tokyo
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Two Parts of the Talk

• Introduction to Pegasus
• Igarashi, UIST 1997 CHI 1998
• Improvement attempts
• My current study
• Any comments greatly appreciated! ?

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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Problem

• Diagrams
• In documents, slides,
• By drawing editors
• Difficult to satisfy geometric relations!

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Example
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(No Transcript)
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Example (contd.)

• In this case, grids works well, but

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Another Example
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The user attempts to draw a perpendicular line,
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but grid prevents desired placements.
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He draws a box separately, and...
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rotates it, but fails to get precise angle.
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Better strategy copy the slope ? rotate 90
degrees
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Why Difficult?
The user must plan detailed strategy.
Planning overhead
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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Our Idea

• Sketching is easy!
• Sketch ? Beautify
• Interactive Beautification Igarashi, UIST 1997

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Interactive Beautification
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Interactive Beautification
Satisfied Constraints
Beautify.
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Interactive Beautification
Beautify.
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Interactive Beautification
Beautify.
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Ambiguity Handling
But free strokes are ambiguous.
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Ambiguity Handling
Generate multiple candidates ? Let the user select
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In this way,the user can constructprecise
geometric diagramswithout any editing commands!!
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Prototype System Pegasus
Live Demo
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Diagrams Drawn
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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Beautification Systems
Pavlidis 1985 ...
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Beautification Systems (contd.)
Batch-based
too many errors!
More Interaction ( multiple candidates)
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Free Stroke Vectorization
Apple Newton SmartSketch ...
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Free Stroke Vectorization (contd.)
Local context
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Free Stroke Vectorization (contd.)
Global context
Local context
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Drawing Systems based on Geometric Constraints
Sutherland 1963 Nelson 1985 ...
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Drawing Systems based on Geometric Constraints
(contd.)

• Previous work
• Explicitly specify constraints
• Our approach
• Infer constraints

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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Beautification Algorithm
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Constraint Inference

• Input
• Reference segments
• (array of (X0, Y0, X1, Y1))
• New stroke
• (x0, y0, x1, y1)

• Output
• Possible constraints
• (linear equations of (x0, y0, x1, y1))

Perpendicular const (x1 x0) const (y1
y0) 0 Edge Connection x0 const, y0
const etc.
(x1, y1)
(x0, y0)
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Constraint Inference (contd.)

• How?
• Supported constraints

if (distance(point1, point2) lt 30) infer
constraint(point1 point2)
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Constraint Solver

• Input
• Possible constraints
• (linear equations of (x0, y0, x1, y1))

• Output
• Beautification candidates
• (array of (x0, y0, x1, y1))

Perpendicular
Same Length
Edge Connection
Horizontal
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Constraint Solver (contd.)
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Candidate Evaluation
Candidate nearest to the original stroke ?
Primary candidate
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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Purpose
To confirm the intuition !
Its difficult for novice users to use
commands
Interactive beautification is good
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Two Measures
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Experimental Settings

• 18 subjects
• 3 diagrams, 3 editors (9 sessions / person)

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Systems

• CAD ... AutoSketch (AutoDesk),
  CAD Software.
• Draw ... SmartSketch (Future Wave),
  Drawing Editor.
• PegasusOur Prototype system.

On AMiTY (a pen computer)
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Diagrams and Constraints
B)
C)
A)
Parallel-1
Symmetric-1
Parallel-1
Parallel-2
Symmetric-2
Parallel-2
Connected (all Vertices)
Perpendicular
Equal Interval
Vertical and Horizontal
Connected (all Vertices)
Connected (all Vertices)
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Results
Precision
Rapidness
Averaged drawing time for three diagrams
The ratio of sessions where all constraints are
satisfied
100
600
500
80
400
60
300
40
200
20
100
0
0
CAD
Draw
CAD
Draw
Pegasus
Pegasus

• Pegasus outperformed CAD and Draw,
• in both rapidness and precision.

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Evaluation Conclusion

• Pegasus cannot do everything
• But certainly useful in its target domain

CAD
Paint
Geometric diagrams, rapidly precisely!
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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Ongoing Work

• Address limitations of Pegasus
• Only lines
• Too many candidates
• Forgets constraints

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Limitation Only Lines

• ? Support curves
• Circles, ellipses, arcs,
• Bézier curves
• (Experimental demo)

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Limitation Only Lines (contd.)

• Challenges with curves
• More ambiguity
• Shape recognition
• Constraint inference
• Complex constraints how to represent?
• e.g. line tangent to piecewise Bézier curve
• Complex constraints how to solve efficiently?
• Exponential growth of candidate solutions

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Limitation Too Many Candidates

• ? Overlapping
• ? Constraint switching interface
• Visualize conflicting constraints
• Enable manual switching
• Challenges
• How to detect conflicting constraints efficiently?

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Limitation Forgets Constraints

• ? Remember constraints
• Maintain them during manipulation
• Chorus Hosobe 2001

Skewed ?
Stretch!
Stretch!
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Outline

• 1. Problem
• 2. Our Idea Demonstration
• 3. Related Work
• 4. Algorithm
• 5. Evaluation
• 6. Ongoing Study
• 7. Summary

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Summary

• Pegasus freehand drawing system
• User study showed promising results
• Geometric constraints play an important role in
  sketch beautification
• Further improvements to be made

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Thank you

• Papers demos available at
• http//www-ui.is.s.u-tokyo.ac.jp/