Exploded Views for Volume DataStefan Bruckner and M. Eduard Gröller

IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 12, NO. 5, 2006

Introduction

The user wants to examine an object of interest within the volumetric data set.

Because of occlusion, normally not all of the data can be shown concurrently.

Introduction (con’d)

Transparency or cutaways can be used to reveal a focus object.

For example reducing opacity of context.

But, parts of the context information are still removed or suppressed.

Exploded view:

The object is decomposed into several parts which are displaced so that internal details are visible.

By increasing the degree of explosion

Related Work

Clipping operations to cut away parts of the volume to reveal internal structures.

Manual editing of volume deformations based on a skeleton.

Selective rendering of components for improved visualization

Exploded views have been investigated in the context of architectural visualization.

The first thorough investigation that uses exploded views for volume visualization was 2003

Generating Exploded Views

Selection Definition

Part Geometry

Force Configuration

Constraint Specification

Interactive Exploded View Rendering

Selection Definition

Two basic objects derived from the volumetric data set. The selection volume:

The degree-of-interest One means most interesting Zero means least interesting.

The background: Everything that is not selected, is part of the background which

represents the context.

Volume Painting used to define the selection.

Selection Definition (con’d)

00011111110

00001111110

00000011000

00000011000

0000001110

00000000000

00000000000

Data Set Selection Volume

Volume Painting

When the user clicks on the image, a ray is cast from the corresponding position on the image plane into the data volume.

At the first non-transparent voxel that is intersected by the ray, a volumetric brush is ”drawn” into the selection volume for each non-transparent voxel within the bounding box of the brush.

Image Plane

Data Set

Part Geometry

Interactive decomposition of a volumetric data set.

The user starts out with a single part which corresponds to the bounding box of the background object.

Axis splitter. Depth splitter. Line splitter.

Force Configuration

No occlusion, but with as little displacement as possible.

Return force: This attractive force tries to move the parts towards their original location.

Explosion force: This force drives the specified parts away from our selection object.

Spacing force: In order to prevent clustering of parts, we also add a repulsive force.

Force Configuration (con’d)

Viewing force: the movement of parts takes into account the current viewpoint.

View-dependent explosions.

Constraint Specification

Constrain the movement of parts.

Interactive addition of joints which restrict the relative movement of parts.

Sliders, hinges, and ball joints

The user can restrict a part from being displaced by assigning an infinite mass.

Sliders and Infinite Mass

Hinges

Interactive Exploded View Rendering

Algorithm: Basic rendering algorithm

perform visibility sorting of the parts

generate initial entry and exit points

perform initial ray casting

for all parts Pi in front-to-back order do

generate entry and exit points for Pi

perform ray casting for Pi

end for

Exploded View Rendering

Performance

GPU-based ray casting algorithm makes use of conditional loops and dynamic branching available in Shader Model 3.0 GPUs.

Comparison with a reference implementation of a conventional single-pass GPU ray caster.

Standard ray casting ignores parts transformation and the selection object.

Performance

Compared to the reference ray caster which achieved 8.97 frames/second

Number of parts

Frames/second

UnexplodedExploded

18.47 (94.4%)7.56 (84.3%)

27.48 (83.4%)7.52 (83.8%)

46.73 (75.0%)6.61 (73.7%)

86.06 (67.6%)5.26 (58.6%)

165.05 (56.3%)4.67 (52.1%)

324.07 (45.4%)3.93 (43.8%)

642.67 (29.8%)2.53 (28.2%)

Questions