A Handheld User Interface for GPU-Accelerated
Large-scale Volume Visualization
Cybermedia Center, Osaka University, Japan

Introduction
The ever-increasing sizes of volumetric data produced from avariety of scientific studies post a formidable challenge for thesubsequent real-time large-scale volume visualization and analysis.
While steady advances in graphics hardware enable faster
rendering, real-time rendering of large-scale volume data is still atough problem. Unlike polygonal data, volume data must take careof transparency of internal values within the volume that thus
requires time-consuming voxel sorting for conventional volumerendering algorithms.
Such large-scale volume visualization must also take into accountinteractive transfer function control for data mining and scientificdiscovery. A high-resolution large screen is often used for
displaying large-scale volume data, in which conventional input
devices such as a mouse and a keyboard is not a practicalsolution.
In this poster, presented is an ongoing work on an interactive
large-scale volume visualization system using a handheld device
and a GPU-accelerated particle-based volume rendering algorithm(see Figure 1).

Particle-based Volume Rendering

Figure 2: System configuration
Table 1: Specification

ServerCPU：AMD Opteron 2350 2.0GHz
RAM：32GB
GPU:nVIDIA Quadro FX 4600
OS:Ubuntu 8.10 (64bit)

ClientMulti-touch Display: 9.7 in
Resolution: 768 x 1024

A set of graphical user interfaces (GUI) are under development (seeFigure 3) for the handheld device. A user will be able to control thevisualization parameters interactively. Example interactions
implemented are:
- Color curve editing. Mapping between a scalar value of voxel
data and its rendered color can be changed simply by deforming
the color curves.
- Particle filtering. Particles with specified values can be hidden orhighlighted.
Any change in visualization parameters will be immediatelyreflected to the rendering result.

To treat large-scale volume data, a particle-based volume
rendering algorithm is employed in our visualization system, which
has been proposed by Kyoto University. In the algorithm, a set oftiny opaque particles are generated from a given 3D scalar field.
The final image is then generated by projecting these particles onto
an image plane. A semi-transparency effect is realized by sub-pixel
processing and averaging and thus the necessity of voxel sorting iseliminated. This algorithm is further accelerated by GPU
programming.

Interactive Transfer Function Control
For assisting data mining and scientific discovery, a handheld
device is provided to control the transfer function in detail in
real-time. Our visualization system consists of a server machine
which renders volume data and a client handheld device (i.e. iPad)that are connected to each other via WiFi or Bluetooth (see Figure2). The hardware specification in our system is summarized inTable 1.
The GPU-based rendering algorithm has been carefully modified toaccept user input to be able to control a variety of visualization
parameters with negligible perform degradation.

Figure 3: User Interface

Conclusion
An interactive visualization system for large-scale volume data has
been proposed. Large-scale volume visualization has been realized
thanks to the GPU-accelerated particle-based volume rendering.
Interactive transfer function control has been realized by a
dedicated graphical user interface on a handheld device.
Kentaro Oita : Graduate School of Information Science and Technology, Osaka University, Japan
Kiyoshi Kiyokawa : Cybermedia Center, Osaka University, Japan
Haruo Takemura : Cybermedia Center, Osaka University, Japan

Contact: Haruo Takemura and Kiyoshi Kiyokawa
E-mail: kiyo@ime.cmc.osaka-u.ac.jp

A Handheld User Interface for GPU-Accelerated Large-scale Volume Visualization

Figure 1: Prototype System