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Freehand Drawing System based on Geometric Constraints. Kaisuke Nakajima Joint work with Takeo Igarashi. User Interface Research Group The University of Tokyo. Two Parts of the Talk. Introduction to Pegasus [Igarashi, UIST 1997 & CHI 1998] Improvement attempts My current study

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Freehand Drawing System based on Geometric Constraints

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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


Two Parts of the Talk

  • Introduction to Pegasus

    • [Igarashi, UIST 1997 & CHI 1998]

  • Improvement attempts

    • My current study

    • Any comments greatly appreciated! 


Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary


Problem

  • Diagrams

    • In documents, slides, …

    • By drawing editors

  • Difficult to satisfy geometric relations!


Example


Copy

Flip

Move


Example (contd.)

  • In this case, grids works well, but…


Geometric constraints

Another Example


The user attempts to

draw a perpendicular line,


GRID

but grid prevents desired placements.


He draws a box separately, and...


ROTATE

rotates it, but fails to get precise angle.


ROTATE

COPY

Better strategy:

copy the slope  rotate 90 degrees


Move

Grid

Flip

Copy

Rotate

Why Difficult?

The user must plan detailed strategy.

Planning overhead


Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary


Sketch

+ Beautify

Our Idea

  • Sketching is easy!

  • Sketch  Beautify

    • Interactive Beautification[Igarashi, UIST 1997]


Draw and...

Interactive Beautification


Draw and...

Interactive Beautification

Satisfied

Constraints

Beautify.


Draw and...

Interactive Beautification

Beautify.


Interactive Beautification

Beautify.


Ambiguity Handling

But free strokes are ambiguous.


Ambiguity Handling

Generate multiple candidates

 Let the user select


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


Prototype System Pegasus

Live Demo


Diagrams Drawn


Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary


Beautification Systems

[Pavlidis 1985] ...


Beautification Systems (contd.)

Batch-based

too many errors!

More Interaction (+ multiple candidates)


Free Stroke Vectorization

[Apple Newton] [SmartSketch] ...


Free Stroke Vectorization (contd.)

Local context


Free Stroke Vectorization (contd.)

Local context

Global context


Drawing Systems based on Geometric Constraints

[Sutherland 1963] [Nelson 1985] ...


Drawing Systems based on Geometric Constraints (contd.)

  • Previous work

    • Explicitly specify constraints

  • Our approach

    • Infer constraints


Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary


Segment coordinates

Constraint Inference

Multiple constraints

Constraint Solver

Multiple candidates

Candidate Evaluation

Primary candidate

Beautification Algorithm


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.)

  • How?

  • Supported constraints

if (distance(point1, point2) < 30)

infer constraint(point1 == point2);


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


Constraint Solver (contd.)


Candidate Evaluation

Candidate nearest to the original stroke

 Primary candidate


Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary


Purpose

To confirm the intuition !

“It’s difficult for novice users

to use commands”

“Interactive beautification is good”


Rapidness

How fast?

Precision

Beautiful?

Two Measures


Experimental Settings

  • 18 subjects

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


Systems

  • CAD ... AutoSketch(AutoDesk), CAD Software.

  • Draw ... SmartSketch(Future Wave), Drawing Editor.

  • Pegasus…Our Prototype system.

On AMiTY (a pen computer)


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)


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

  • Pegasus cannot do everything

  • But: certainly useful in its target domain

CAD

Paint

Geometric diagrams,

rapidly & precisely!


Outline

1. Problem

2. Our Idea & Demonstration

3. Related Work

4. Algorithm

5. Evaluation

6. Ongoing Study

7. Summary


Ongoing Work

  • Address limitations of Pegasus

    • Only lines

    • Too many candidates

    • Forgets constraints


Limitation: Only Lines

 Support curves

  • Circles, ellipses, arcs,

    Bézier curves

  • (Experimental demo)


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

Overlapping…

 Constraint switching interface

  • Visualize conflicting constraints

  • Enable manual switching

  • Challenges

    • How to detect conflicting constraints efficiently?


  • Limitation: Forgets Constraints

     Remember constraints

    • Maintain them during manipulation

    • Chorus [Hosobe 2001]

    Skewed 

    Stretch!

    Stretch!


    Outline

    1. Problem

    2. Our Idea & Demonstration

    3. Related Work

    4. Algorithm

    5. Evaluation

    6. Ongoing Study

    7. 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

    • Papers & demos available at

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


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