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Title
New perspectives to save cultural heritage
Author
Altan, M. Orhan

A NEW APPROACH FOR 3D MODELS TRANSMISSION
A. Guamieri a , F. Pirotti \ M. Pontin a , A. Vettore a
a CIRGEO, Interdept: Research Center of
Cartography, Photogrammetry, Remote Sensing and GIS
University of Padova, Agripolis
35020 Legnaro (PD) - Italy
e-mail: antonio.vettore@unipd.it; cirgeo@unipd.it
KEYWORDS: 3D modeling, Internet, data compression, documentation, data retrievial, VR
ABSTRACT
The visualization and interactive navigation of 3D models, like virtual visits of museums, churches or even whole cities (cybercity
models), are gaining a more and more increasing use and importance with time. This has been accomplished in last years thank to the
augmented power of modem CPUs, graphic hardware devices and thank to a wider access to the web. Even in the survey field the
interest towards 3D models has grown, given the advantages offered by ground-based laser scanners in terms of survey time and the
pretty good quality of obtained 3D models. Indeed, several tests and applications have been performed so far all around world with
such instruments: 3D data have been collected from objects of different shape and size, ranging from cultural heritage to land
infrastructures, accuracy has been investigated and corresponding 3D models have been created using appropriated software. Beside
issues related to the accuracy and the quality of resulting models, another interesting topic should be considered: the remote use of
these 3D models, i. e. how they can be optimally transmitted over the web.
To this aim we have developed a VRML split-browser, i.e. a 3D model visualization shared system based on two different server-
side and client-side applications. The former executes the rendering of the scene and send it to the client, which is located on the
remote PC of the user. In turn, the client provides the user with a graphical interface to explore the 3D model interactively.
The system is based on image compression and projective transformations, which allow to share the 3D models over the web with
limited throughput to the client. In this paper, we will present the frame prediction algorithm, based on a space displacement of the
viewpoint and the way adopted to apply it in the remote visualization system.
1. INTRODUCTION
Over last times, the 3D modeling of real objects, of whatever
size and complexity, is gaining a more and more interest and
importance by the scientific community. For instance, the
availability of close-range and long-range ground-based laser
scanners, which are able to collect several thousands of
points in short time, have increased the interest towards 3D
models as a useful and alternative mean for analysis and
study in the field of medicine, industry, cultural heritage,
engineering, architecture, etc. Tests and applications have
been extensively performed all around the world in order to
assess the accuracy and the quality of those 3D models.
Beside such topics, another interesting issue should be
considered: the remote use of these 3D models, i. e. how
they can be optimally transmitted over the web.
To this aim we have developed a VRML split-browser, i.e. a
3D model visualization shared system based on two different
server-side and client-side applications. The main advantage
of proposed solution relies on the fact that the server sends to
the client a periodic image sequence, composed by a
reference image and a set of error images, instead of the
whole VRML model. Basically, the server executes the
rendering of the scene and sends it to the client, which is
located on the remote user’s PC. In turn, the client provides
the user with a graphical interface to explore the 3D model
interactively. Thus, using suited image compression techni
ques and projective transformations, 3D models can be
shared over the web with limited throughput to the client.
Though the developed technique looks like the algorithms
implemented in the MPEG compression, in this case the key-
advantage relies on the a-priori knowledge of the image
transformation parameters, as they are determined directly by
the request of viewpoint change made by the user through the
client GUI.
In this paper, we will present the frame prediction algorithm,
based on a space displacement of the viewpoint and the way
adopted to apply it in the remote visualization system.
The paper is structured as follows. In the section 2 a short
overview of the VRML language is provided, highlighting
the disadvantages that show up when large 3D data sets are
employed. In section 3 we describe the framework of our
VRML split-browser, we developed in order to improve the
remote transmission of 3D data. Then, section 4 focuses on
the mathematics which the implemented frame compression
algrotihm is based on, while in section 5 the results of the
tests performed using simple geometric shapes are presented.
Finally, section 6 reports the conclusions.
2. THE VRML LANGUAGE
Technically speaking, VRML is neither virtual reality nor a
modeling language; at its core, VRML is simply a 3D
interchange format. It defines most of the commonly used
semantics found in today's 3D applications such as
hierarchical transformations, light sources, viewpoints,
geometry, animation, fog, material properties, and texture