Scalable Devices - Scientific Visualization: Uncertainty, Multifield, Biomedical, and Scalable Visualization - page 345

29.2.2.1 Remote Rendering
One solution to circumvent the limitation of the mobile device's graphics hardware
is not to rely on it for the complex rendering tasks required for many visualization
algorithms but to let a server do the rendering work and to transfer the rendered
image to the mobile device. In 2005 Lluch et al. [ 39 ] presented such a client/server
rendering system. In their system a server holds a scene graph and uses it, along with
client view information, to select an appropriate resolution from a multi-resolution
representation on disk. Scene access is done in an out-of-core fashion, allowing
very large models to be visualized. Even when rendering is done on the server, for
large data a single machine may not be able to provide updates to the mobile device
quickly enough for mobile users. For this reason Lamberti and Sanna [ 38 ] introduce
a Chromium-based [ 26 ] rendering system which encodes the data as MPEG and
streams it to be decoded on the mobile device. With motion estimation being the most
expensive process of MPEG4 encoding, Cheng et al. [ 11 ] are able to significantly
improve this step by directly retrieving motion vectors from information available in
the rendering pipeline.
More recently, this area of research has matured from the stage of developing
the basic building blocks, to presenting solutions for specific problems, and demon-
strating the practical use of mobile visualization. Park et al. [ 47 ] developed a system
for collaborative medical visualization, using parallel server-based volume rendering
techniques, while Meir and Rubinsky [ 41 ] investigate the use of mobile devices as a
cost-effective component of a distributed system for performing ultrasounds. Their
system combines simple-to-use, inexpensive ultrasound devices at the client site,
which generate ultrasound data. The data is sent to a server which performs volume
rendering at pre-defined camera angles, and sends the images back down to mobile
devices for analysis in the field.
29.2.2.2 Client Based Rendering
In a client based setting the entire rendering workload is handled solely by the
mobile device and no persistent server connection is required for the visualization.
A network connection may be required for some initial data transfer but for the
visualization itself no server connection is necessary. In the first work that does
3D visualization with only the mobile hardware resources, Burigat and Chittaro [ 6 ]
described a VRML-based system for visualizing what a user sees as they roam a city.
A similar approach was taken by Nadalutti et al. [ 44 ] based on the X3D standard.
Moser and Weiskopf [ 43 ] were the first to present a prototypic client-only inter-
active volume rendering application on mobile devices. Due to the lack of 3D texture
support by the OpenGL ES GPU their work is based on the concept of axis aligned
slices as proposed by Rezk-Salama et al. [ 54 ].
Similar to the remote rendering works, one can also observe for the client based
rendering systems that both the hardware as well as the methods have reached a
state that allows for implementations to leave the stage of research prototypes and to