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Two Parts of the Talk. Introduction to Pegasus[Igarashi, UIST 1997

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freehand drawing system based on geometric constraints

Freehand Drawing Systembased on Geometric Constraints

Kaisuke Nakajima

Joint work with Takeo Igarashi

User Interface Research Group

The University of Tokyo

two parts of the talk
Two Parts of the Talk
  • Introduction to Pegasus
    • [Igarashi, UIST 1997 & CHI 1998]
  • Improvement attempts
    • My current study
    • Any comments greatly appreciated! 
outline
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

problem
Problem
  • Diagrams
    • In documents, slides, …
    • By drawing editors
  • Difficult to satisfy geometric relations!
slide6
Copy

Flip

Move

example contd
Example (contd.)
  • In this case, grids works well, but…
slide9
The user attempts to

draw a perpendicular line,

slide10
GRID

but grid prevents desired placements.

slide12
ROTATE

rotates it, but fails to get precise angle.

slide13
ROTATE

COPY

Better strategy:

copy the slope  rotate 90 degrees

why difficult
Move

Grid

Flip

Copy

Rotate

Why Difficult?

The user must plan detailed strategy.

Planning overhead

outline15
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

our idea
Sketch

+ Beautify

Our Idea
  • Sketching is easy!
  • Sketch  Beautify
    • Interactive Beautification[Igarashi, UIST 1997]
interactive beautification18
Draw and...Interactive Beautification

Satisfied

Constraints

Beautify.

ambiguity handling
Ambiguity Handling

But free strokes are ambiguous.

ambiguity handling22
Ambiguity Handling

Generate multiple candidates

 Let the user select

slide23
In this way,the user can constructprecise geometric diagramswithout any editing commands!!
outline26
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

beautification systems
Beautification Systems

[Pavlidis 1985] ...

beautification systems contd
Beautification Systems (contd.)

Batch-based

too many errors!

More Interaction (+ multiple candidates)

free stroke vectorization
Free Stroke Vectorization

[Apple Newton] [SmartSketch] ...

free stroke vectorization contd31
Free Stroke Vectorization (contd.)

Local context

Global context

drawing systems based on geometric constraints
Drawing Systems based on Geometric Constraints

[Sutherland 1963] [Nelson 1985] ...

drawing systems based on geometric constraints contd
Drawing Systems based on Geometric Constraints (contd.)
  • Previous work
    • Explicitly specify constraints
  • Our approach
    • Infer constraints
outline34
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

beautification algorithm
Segment coordinates

Constraint Inference

Multiple constraints

Constraint Solver

Multiple candidates

Candidate Evaluation

Primary candidate

Beautification Algorithm
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))

Constraint Inference

Perpendicular

const * (x1 – x0) + const * (y1 – y0) = 0

Edge Connection

x0 = const, y0 = const

etc.

(x1, y1)

(x0, y0)

constraint inference contd
Constraint Inference (contd.)
  • How?
  • Supported constraints

if (distance(point1, point2) < 30)

infer constraint(point1 == point2);

constraint solver
Input

Possible constraints

(linear equations of (x0, y0, x1, y1))

Output

Beautification candidates

(array of (x0, y0, x1, y1))

Constraint Solver

Perpendicular

Same Length

Edge Connection

Horizontal

candidate evaluation
Candidate Evaluation

Candidate nearest to the original stroke

 Primary candidate

outline41
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

purpose
Purpose

To confirm the intuition !

“It’s difficult for novice users

to use commands”

“Interactive beautification is good”

two measures
Rapidness

How fast?

Precision

Beautiful?

Two Measures
experimental settings
Experimental Settings
  • 18 subjects
  • 3 diagrams, 3 editors (9 sessions / person)
systems
Systems
  • CAD ... AutoSketch(AutoDesk), CAD Software.
  • Draw ... SmartSketch(Future Wave), Drawing Editor.
  • Pegasus…Our Prototype system.

On AMiTY (a pen computer)

diagrams and constraints
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)

results
Precision

Rapidness

Averaged drawing time

for three diagrams

The ratio of sessions where

all constraints are satisfied

Results

100

600

500

80

400

60

300

40

200

Pegasus outperformed CAD and Draw,

in both rapidness and precision.

20

100

0

0

CAD

CAD

Draw

Pegasus

Draw

Pegasus

evaluation conclusion
Evaluation: Conclusion
  • Pegasus cannot do everything
  • But: certainly useful in its target domain

CAD

Paint

Geometric diagrams,

rapidly & precisely!

outline49
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

ongoing work
Ongoing Work
  • Address limitations of Pegasus
    • Only lines
    • Too many candidates
    • Forgets constraints
limitation only lines
Limitation: Only Lines

 Support curves

  • Circles, ellipses, arcs,

Bézier curves

  • (Experimental demo)
limitation only lines contd
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
limitation too many candidates
Limitation: Too Many Candidates

Overlapping…

 Constraint switching interface

      • Visualize conflicting constraints
      • Enable manual switching
  • Challenges
    • How to detect conflicting constraints efficiently?
limitation forgets constraints
Limitation: Forgets Constraints

 Remember constraints

  • Maintain them during manipulation
  • Chorus [Hosobe 2001]

Skewed 

Stretch!

Stretch!

outline55
Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary

summary
Summary
  • Pegasus: freehand drawing system
    • User study showed promising results
  • Geometric constraints play an important role in sketch beautification
  • Further improvements to be made
thank you
Thank you
  • Papers & demos available at

http://www-ui.is.s.u-tokyo.ac.jp/

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