iMAGIS-GRAVIR / IMAG

Drawing for Illustration andAnnotation in 3D

David Bourguignon*, Marie-Paule Cani* and George Drettakis**

*iMAGIS, INRIA Rhône-Alpes, France

**REVES, INRIA Sophia-Antipolis, France

iMAGIS-GRAVIR / IMAG

Motivation•Drawing

– Scene complexity in an effective manner– Indication of uncertainty– Limitation to single

viewpoint

•Applications– Fine arts– Teaching– Early stages of design

Human heart

iMAGIS-GRAVIR / IMAG

Motivation• Goal: drawing in 3D

– Augment strokes to true 3D entities

– Free-form drawing

– Annotation of existing 3D models

– Many viewpoints

• Problems to be solved– Silhouette stroke modeling

– Silhouette stroke rendering from different viewpoints

EyeBack

iMAGIS-GRAVIR / IMAG

Overview

• Previous work

• Contributions– Silhouette stroke modeling

– Silhouette stroke rendering

– Interface for drawing

• Results

iMAGIS-GRAVIR / IMAG

Previous Work[Akeo et al., 1994][Pugh, 1992]

2D drawing is converted to 3D

Specify hidden parts by hand

iMAGIS-GRAVIR / IMAG

Previous Work

[Lipson and Shpitalni, 1996] [Eggli et al., 1997]

No free-form drawing Limited number of primitives

iMAGIS-GRAVIR / IMAG

Previous Work

[Cohen et al., 1999] [Tolba et al., 1999]

3D curves design,no drawing

2D drawings reprojected,no visibility changes

iMAGIS-GRAVIR / IMAG

Previous Work

[Igarashi et al., 1999][Zeleznik et al., 1996]

Limited to a given gestural interface

Closed strokes only

iMAGIS-GRAVIR / IMAG

Previous Work

[Cohen et al., 2000]

Drawing modes adapted to landscaping only,no 3D model reconstruction in billboard mode

iMAGIS-GRAVIR / IMAG

Overview

• Previous work

• Contributions– Silhouette stroke modeling

– Silhouette stroke rendering

– Interface for drawing

• Results

iMAGIS-GRAVIR / IMAG

Our Approach•Strokes

– 2D drawing on the screen plane– Line stroke for 1D details– Silhouette stroke for

view-dependent information

•Problems to be solved– Inferring local surface from

silhouette– Representing uncertainty– Managing occlusions

Silhouette stroke

Line stroke (3D spline)

iMAGIS-GRAVIR / IMAG

Overview

• Previous work

• Contributions– Silhouette stroke modeling

– Silhouette stroke rendering

– Interface for drawing

• Results

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Modeling• Infer local surface

– Fit Bézier curve to 2D user input– Evaluate local curvature– Process curvature vectors

• Clamp relatively to inflexion points

• Set consistent in/out orientation

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Modeling• Infer local surface

– Fit Bézier curve to 2D user input– Evaluate local curvature– Process curvature vectors

• Clamp relatively to inflexion points

• Set consistent in/out orientation

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Modeling• Infer local surface

– Fit Bézier curve to 2D user input– Evaluate local curvature– Process curvature vectors

• Clamp relatively to inflexion points

• Set consistent in/out orientation

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Modeling• Infer local surface

– 3D circles from vectors of curvature– Local Bézier surface

iMAGIS-GRAVIR / IMAG

Overview

• Previous work

• Contributions– Silhouette stroke modeling

– Silhouette stroke rendering

– Interface for drawing

• Results

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Rendering• New silhouette from new viewpoint

– Efficient silhouette approximation using clipping planes

– Good for local surfaces associated with strokes

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Rendering•Represent uncertainty

– Use stroke texture– Color stroke as desired

Front(original view)

Side (30°)

Side (90°)

Strokealpha texture

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Rendering•Manage occlusion

– Use occluder texture for soft occlusion– Various drawing styles

Occluderalpha texture

iMAGIS-GRAVIR / IMAG

Silhouette Stroke – Rendering

• Multipass algorithm(Previously render scene and line strokes)

– First pass: Rendering silhouette strokes• With stroke texture

• With stroke color

– Second pass: Soft occlusion by local surfaces (set depth)• With occluder texture

– Third pass: Soft occlusion by local surfaces (achieve blend)• With occluder texture

• With occluder color

iMAGIS-GRAVIR / IMAG

Overview

• Previous work

• Contributions– Silhouette stroke modeling

– Silhouette stroke rendering

– Interface for drawing

• Results

iMAGIS-GRAVIR / IMAG

Interface for Drawing

•Two types of strokes– Line stroke– Silhouette stroke

•Two drawing modes– In empty space– Relatively to other objects

On one objectBetween two objects

iMAGIS-GRAVIR / IMAG

Overview

• Previous work

• Contributions– Silhouette stroke modeling

– Silhouette stroke rendering

– Interface for drawing

• Results

iMAGIS-GRAVIR / IMAG

Applications• Illustration in 3D

iMAGIS-GRAVIR / IMAG

Applications•Annotation of a 3D scene

iMAGIS-GRAVIR / IMAG

Applications•"Guided design"

iMAGIS-GRAVIR / IMAG

Video

iMAGIS-GRAVIR / IMAG

Conclusion•System for drawing in 3D

– View-dependent strokes with occlusion– Useful for drawing simple scenes in 3D– Useful for annotations

•Future work– Handling tubular objects– Real world test: using it to teach anatomy

iMAGIS-GRAVIR / IMAG

Acknowledgements

• Eric Ferley for feedback throughout the project• Laurence Boissieux for creating some of the drawings,

Marc Pont for help with models• Frédo Durand for advice on the paper

iMAGIS is a joint project of CNRS, INPG, INRIA and UJF

iMAGIS-GRAVIR / IMAG