Exploded Views for Volume Data Stefan 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) Data SetSelection 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 P i in front-to-back order do generate entry and exit points for P i perform ray casting for P i 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 Frames/secondNumber of parts ExplodedUnexploded 7.56 (84.3%)8.47 (94.4%) (83.8%)7.48 (83.4%) (73.7%)6.73 (75.0%) (58.6%)6.06 (67.6%) (52.1%)5.05 (56.3%) (43.8%)4.07 (45.4%) (28.2%)2.67 (29.8%)64

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