REAL-TIME INTERACTIVE RECONSTRUCTION OF ARCHAEOLOGICAL
LANDSCAPES: AN OPENSOURCE APPROACH
FROM GIS TO VIRTUAL REALITY
L. Calori a, M. Forte b, S. Pescarin b
a
b
CINECA, Supercomputing Center, via Magnanelli 6/3, Casalecchio di Reno – BO, Italy - ([email protected])
CNR ITABC (Institute of Technologies Applied to Cultural Heritage), via Salaria km 29,300, 00016 Monterotondo St.
(Rome), Italy ([maurizio.forte],[sofia.pescarin]@itabc.cnr.it), www.itabc.cnr.it/VHLab
KEY WORDS: Virtual Heritage, Landscape Reconstruction, Terrain Generation, Web application, OpenSource
ABSTRACT:
The development of 3D real-time visualisation of geographical data (GIS and remotely sensed data) allows today the use of DVR
(Desktop Virtual Reality) systems not only to communicate final results of scientific studies, but also for the process itself of
analysis, interpretation and reconstruction of archaeological landscapes. The paper will be focused on a new approach based on
OpenSource projects that, we believe, can produce positive results in the field of Cultural Heritage, and most of all of Virtual
Heritage. Some testing cases will be discussed on the generation at different levels of detail (LOD) of territorial data, on the
interaction with the archaeological landscape of the Appia Antica Park in Rome and on the publication of the three-dimensional
landscape over the Web, based on OpenSceneGraph and Virtual Terrain Project.
INTRODUCTION
Introduction. The digital revolution
If we analyse last years trend in the field of Geographical
Information Systems, we can clearly notice how wide has
become the interest towards 3D visualisation; most of the
software packets have added or implemented 3D extensions.
On the other side computer games are spreading off quite
rapidly. Almost the entire new kids generation (in Europe, US
and in many parts of Asia) knows and tried a computer-game or
possesses a ‘playstation’, ‘x-box’ or similar: real time Computer
Graphics is becoming a common experience part of everyday
life.
Behind this, there’s surely a component connected with
entertainment, pushed by a strong economic interest. Other
sectors can hardly obtain the same kind of investments,
although the research activity and the philosophical theorisation
already have indicated, in the last decade, some potential future
developments that could possibly change the approach toward
cultural information (Barcelo, Forte, Senders, 2000).
Archaeology, History, Art fields started their first experience in
computer-graphics and 3d visualisation in the ‘80s. Our
experience, of CNR ITABC and CINECA Visit Lab, has got
through many phases before reaching to last applications on
Desktop Virtual Reality Systems (Calori, Guidazzoli, Forte
1996, Forte 1997; Forte et alii 2000).
Although the revolution of digital technologies is commonly
treated mainly from a technological point of view, we would
like to underline the importance even of a cultural point of
view. We believe in fact that Virtual Reality systems could be
an answer to many questions, increasing their application (in
quality and quantity) in the next years to many fields, but with a
strong theoretical epistemological discussion. We would like to
discuss about technological issues according to an ecological
and cybernetic viewpoint (Maturana, Varela, 1980, 1987;
Bateson, 1972; Forte et alii, 2001). We believe, indeed, that the
Virtual, first of all, is an environment and an ecosystem.
According to an ecosystemic perspective the Virtual represents
a complex of relations, an ecosystem. The virtual translation of
heritage is explainable according to a connectivity of
information creating a system.
According to this methodological approach the information
processing correlated to heritage is able to modify its
interpretation, its value. We could say that the last goal of the
digital processing is the perceptive and cognitive increasing of
the thing-cultural heritage, digital access to the virtuality (then
with feedback) of the cultural information.
Virtual Heritage, and in particular archaeology, presents often
interesting case-studies due to their complexity and to the strict
needed connection with spatial (and temporal) components.
Landscapes and sites (at a macro and micro scale) can be treated
as perfect interfaces with cultural information, perfect
connectors among cultural objects, time-components, contents,
spatial information, diachronicity, social and anthropological
aspects.
With a VR system it’s possible to access even complex contents
very easily, to assemble different data and experience them, to
recreate lost contexts, to reflect over historical topics as over
anthropological ones.
Unfortunately the story of last decades CG applications in the
field of Cultural Heritage is a story of powerful reconstruction
environments, with no behaviours or interactions apart from the
movements of the user inside the 3d space. These applications
were visible just on expensive workstations, not accessible
freely by a public users, but they were driven by a human
operator. In most cases they have been accessed, especially in
the case of real-time VR, only by small communities, remaining
inside laboratories, universities, computing centres. And this is
today almost unacceptable if we think the investment required
for such VR systems compared to Cultural Heritage general
economical policy and to effective benefit of these
reconstructions.
The distribution of cultural information is surely a key-issue for
the future of the knowledge of Cultural Heritage, that will be
committed to new complex systems, different from the
traditional linear systems. A crucial problem indeed is the
transmissiblity of more and more composite information,
through complex VR systems that need to be studied by
interdisciplinary and international teams in term of
communication and interfaces.
The research, but also the worldwide community, require more
interactive systems, more dissemination and data sharing
possibilities, step by step information control, updatable and
open systems.
Ancient Landscape Reconstruction
Virtual reality systems, thanks to data integration potentialities,
can re-create connection between information and create new
information.
The possibility to compare data and information allows an
increasing of the knowledge (Bateson, 1972). So in order to
obtain a spatial Virtual Reality System we have to make data
‘comparable’ in overlay, keeping its spatial component. A GIS
project has to be constructed at the bottom of any further project
development. Even Databases have to be possibly planned in
connection with vectorial and spatial information, while 3D
models can be modelled even apart, but with particular attention
to their geographic position and to their use for real time and
web publishing purposes. Inside the Geographical Information
System data are prepared to be used in the VR application:
DEM, Geoimages and Vectorial thematic layers (Culture).
Keeping data spatial component allows, even inside a VR
system, to do some spatial analysis, creating new interpretations
and new information. This information can be used to update
the GIS, as new thematic layers, in a sort of “virtuous circle”.
What we obtain is a Virtual Reality application based on a
Geographical Information System, characterized by the
possibility of sharing data, exchanging information, testing
different reconstructions and revising data (Fig1).
real time spatial virtual environment. Thanks to this kind of
tools it’s possible to maintain the complete spatiality of the data
(Forte et alii 2003). On the other side the use of software,
personalized (such in the case of VirTools) or appositely
created and programmed (VISMAN: Calori et alii 2003, Calori
et alii 2004), to visualise and interact with those data, directed
us to a development in the realisation of complex VR
applications.
The reconstruction of a landscape, present past or even future
landscape, can be achieved through different steps:
1. study of the content
2. processing of a GIS project
3. processing of one or more Virtual Reality projects;
this step includes even: terrain generation, 3d
modelling, database and multimedia resources
creation.
4. realisation of a VR application characterised by a
certain number of behaviours or interaction inside the
VR environment (VISMAN/VIRTOOLS).
Figure 2. Scheme of the digital protocol
Thanks to CINECA experience in the field of OpenSource we
are trying now to orient new research activities (applied to
landscape and archaeology) towards: the use of a complete
OpenSource approach in the steps 2 and 3, replacing where it’s
possible, traditional tools with open software, and creating a
new sector of applications open and web-based.
In this way we think that the introduction of the concept of
OpenSource in the field of Cultural Heritage will be real
challenge for its future developments, based on its economic
impact, sustainability, flexibility, adaptability and on its strong
push towards interdisciplinary and multidisciplinary work,
towards data, technologies and methodologies exchanges.
A new digital protocol is being signed by the two
interdisciplinary teams on this topic.
Figure 1. GIS and Virtual Reality connection.
In the last years we have obtained some reasonable results in the
field of ancient landscape reconstruction through digital
technologies (Forte, Williams, 2001; Forte, 2003). This allowed
us to define a digital protocol (Fig.2) in which is schematically
exemplified the methodology we use to study, reconstruct and
generate 3D dimensional landscapes, accessible in real time in a
Virtual Reality environment on a Desktop PC (Forte et alii,
2004).
The use of Terrain Generator has been surely a turning point in
the integration of different typologies of data available, inside a
OpenSource: a challenge for Cultural Heritage
New research activities have been activated since 2004 and they
have been focused on OpenSceneGraph library for paged terrain
generation, through an OSG tool called OSGdem, and on
Virtual Terrain Project (another open project based on
OpenSceneGraph). Two dissertations have been assigned on
this topic and a workshop (“OpenSource and Archaeology”) has
been organised with surprising results. This workshop, held in
occasion of the international conference CAA2004 – Computer
Application in Archaeology (organised by Calori, Hermon,
Niccolucci, Pescarin), stress the importance of the argument and
encouraged CNR ITABC to open a new parallel research
activities on OpenSource and Cultural Heritage, based even on
a cooperation with CINECA Visit Lab, offering testing cases
and reporting this experience through material, tutorials,
documentations to be published.
We have chosen to orient our framework on the platform
OpenSceneGraph for many reasons. First of all for its
portability. As will be discussed in charter 2.2, OSG is available
for Linux, Window and SGI. It’s possible to find examples of
applications with different GUI and even with ActiveX
modules. Its compatibility with modelling standards is also very
important: OpenSceneGraph manages in fact .flt and .3ds
models, paged terrains produced with other software such as
Terrex Terravista (flt, txp). Moreover there are also available
exporters for 3ds Max, Maya and Blender. Even its performance
can be considered a good quality of this library, allowing
advanced rendering techniques, such as vertex and fragment
shaders, MultiTexturing, shadows, impostors, etc. Pagingnetworking possibilities make OpenSceneGraph open to use
paging techniques for terrain generation (as TerraPage formats).
. maintain the same modelling formats of 3d objects
reconstructed with photo-modelling or scanner-laser techniques
and processed with external software, such as 3DStudio Max
(3ds, flt, osg, ive)
. create libraries of 3d models and vegetation typical of the
area and of the period
. connect directly inside the three-dimensional geographical
space the models (fig.3) and the vectorial themes (shp files)
(with VT Builder and VTP Enviro).
. working dynamically at the reconstruction of the visible
archaeological landscape, testing hypothetical thesis, preparing
the data for a complex VR application, based on story-telling
approach (based on VirTools: www.virtools.com).
. and finally publish the results of the surveys over the Web,
updating them at each new campaigns through an ActiveX
component realised by CINECA Visit Lab team (fig.5).
OPENHERITAGE VR SYSTEMS
Real Time 3D landscape reconstruction: the case of Appia
Archaeological Park and Certosa Museum project
In two cases we have experimented the new protocol: the
“Appia Antica project” and the “Certosa project”.
We have chosen these two case-studies even because they have
different aims; in this way we could test how our methodology
could be applied in the two main activities connected with
Cultural Heritage: research-mapping-management-conservation
and dissemination-didactic-musealisation.
In the case of the Appia project, in 2002 CNR-ITABC signed a
research
agreement,
together
with
the
Municipal
Superintendence of Rome, that regarded the realisation of
mapping activities inside the archaeological park and the
realisation of a bi-dimensional and three-dimensional database
of the monuments of the Appia Park in Rome.
Two CNR-ITABC research teams are working (the project will
end in 2006), at the project with different purposes: topographic
survey, architectonic aspects of the monuments with stereophotogrammetric techniques (Salonia et alii, 2003) and virtual
reconstruction of the archaeological landscape, starting from
data acquired directly on the field. Part of the effort was
dedicated to the creation of a VR system that could be a
research and co-operative working tool, during the phases of
the project, and a complex VR application in a future
documentation and museum centre that could be realised inside
the park.
The use of OpenSource tools changed the approach even to VR,
leading to the creation of personalised spatial tool useful to:
. link/connect all the data that were acquired during the survey
campaigns in the Appia park
. keep the same geographical projection used in the realisation
of the GIS
. maintain the same GIS formats of data (DEM in ascii grid
format, vectorial shape files, geotiff and geojpg)
. generate quality paged and tiled terrains of the area from GIS
data (with OSGdem)
Figure 3. The Appia park during the reconstruction phase
inside VTP Enviro (modified version)
The “Certosa project” is a project of Bologna City Council
(New Institutions for Communicating the City) and CINECA.
It is currently developing a virtual museum for the city, a
complex VR application regarding several cultural that will
constitute the basis of a Museum for Accessing the City of
Bologna. The fundamental idea is the visual mediation. An
interactive visual portal is the access to historical and cultural
contents. Choices are guided by vision and the virtual
environment presents information in a user friendly manner.
The actual territory that the application can visualize is the
second most important concept around which the application
revolves. This aspect enables a user to put into relation different
historical events and topics, gathered under the same context
that unifies dispersed cultural resources. For the development of
this application three different sites (two in Bologna and one in
its surroundings) have been selected as a starting point for the
process of valorization: the Certosa monumental cemetery, that
include several significant monuments and even an
archaeological Bronze Age site: an Etruscan necropolis; the
Memorial Wall, a monument raised in remembrance of the
Bolognese people killed in the fight for liberation during the
Second World War; and the area of Monte Sole park, sadly
known for the mass executions of civilians carried out during
the Second World War (LIGUORI et alii 2004).
The VR application was developed inside the VISMAN
framework, based on SGI Performer.
During the development of the Etruscan part of the application,
there was the necessity of starting a co-operative reconstruction
project for the Bronze Age landscape, together with the
archaeological museum experts. This led us to approach the
problem carefully and in a updateable, open and scientific way,
before getting to the VR application whose primary goal was
the dissemination and musealisation of the Certosa history.
Such in the case of Appia Antica project, OpenSource tools
allow to follow this approach. A GIS base was constructed, a
database was realised and connected with the georeferenced
object. A first attempt of Etruscan DEM and GeoImage was
realised. The 3D terrain was generated with Terrex Terravista
because we needed FLT flight files in the following phase
(Visman). GIS vectorial layers and the terrain were imported in
a modified version of VTP Enviro (Camporesi, 2005), that was
used as 3D environment to reconstruct dynamically the
archaeological landscape (fig.4 right). With Enviro it was
possible: to connect 3d models of the steles and other
archaeological objects in the position where archaeologists
found them during 18th century excavations; create library of
plants known to be typical of that area during the Bronze Age
and add in real time the vegetation; control parameters and
hypothesis in 3D.
Although the project is at beginning we have found that the
approach used created a collaborative connection between
different institutions and disciplinary teams, opening positive
discussions aimed at landscape reconstruction, while at the
bottom a scientific digital basis is prepared (GIS, DB) and
continuously updated.
Figure 4. Construction of the GIS, reconstruction phase of the
landscape inside VTP Enviro
OpenSource components
As we describe above, as real time scenegraph library we use
OpenSceneGraph (OSG, www.openscenegraph.org). This
library, based on OpenGL, offers the following features:
Crossplattform (Windows, Linux, Irix)
Real Time optimisation
Wide range of input format support (flt, 3ds, obj, osg,
ive)
Extensible through-plug-in architecture
Built in support of paged lod terrain generation and
navigation
OSG already provides both a tool to generate hierarchical paged
terrains from Geoimages and Digital Elevation Models and a
network loader capable of providing browsing of such
hierarchies with reasonable bandwidth requirements.
The generation tool (OSGdem) has been used to build a base
paged virtual terrain models of our test-cases. OSGdem
produces the hierarchy of terrain patches as a directory of .ive
native optimized and compressed .osg format files. By exposing
this directory to the Web (we have used a simple Apache Web
Server) it’s possible to use the example viewer tool
(OSGviewer) to browse the terrain by opening the topmost
archive file.
The built-in paged LOD engine of OSG takes care of loading
the required terrain patches, according to the user selected view
position and orientation; the framerate is kept as constant as
possible, while the background thread keeps increasing the
detail of the loaded tile-patches. OSGviewer is available on
both Windows and Linux.
Even if OSGdem can produce good quality paged terrains, it
does not handle any culture data or 3d models.
On the contrary, as explained, we use VTP Enviro in order to
interactively modify the landscape, adding and modifying
culture data and 3d models, taking them from 3d libraries.
Enviro and VTBuilder are tools developed within the Virtual
Terrain Project software framework (www.vterrain.org).
VTBuilder allows processing of GIS culture data (such as tree
coverage, river and road centrelines, lakes, etc), Digital
Elevation Models and Geoimages and produces a 3D landscape
database (stored as XML file format).
Enviro is an interactive browser and editor of such database.
Both tools are cross platform and released under OpenSource
licence.
Unfortunately the VT terrain database is not well suited for
large terrains network walk through, because it does not provide
paged terrain structure.
Thus, in order to support our virtual reconstruction project, we
decided to integrate OSGdem and VTP Enviro. Enviro already
uses OSG as rendering library, so the integration work has been
reasonable.
Within the effort of a thesis dissertation, Enviro has been
extended as to allow osg/ive terrains import, in this way the
native Enviro base DEM (bt format) can be substituted with a
more efficient OSGdem hierarchy. The Enviro user can now
access all the Enviro interactive editing functionalities with a
OSG terrain. At the end of the interactive section, the user can
save the culture data within the existent OSGdem paged terrain
structure. The result is a paged terrain with culture 3d data on it
(trees, streets, buildings, sites, labels, etc.).
Exported data, structured in this way, can be browsed with
OSGviewer, as we have mentioned before.
In order to improve Web presentation, all the necessary OSG
components have been assembled into an ActiveX Internet
Explorer plug-in. At present the status of this part of the
framework is still under development at CINECA
Supercomputer Centre.
CONCLUSION
1.1 A sight into the future
Since last releases of OpenSceneGraph it’s quite clear the
direction and potentialities of this library for the publication of
large and complex territories over the Web.
The work we have done until now is simplifying the production
of 3D landscape useful for real-time navigation of any user,
even from home, without having to download locally huge
amount of data.
After these experiences we planned further developments. The
goal we would like to reach is the creation of a 3d shared and
interactive working system, web based.
We are planning to combine different Open Source
technologies, based mainly on OSG library, and to obtain an
environment whose modelling and reconstructing aspects are
accessible and adjustable through the Web.
Some experimental tests has already been done in this direction.
The complete system we are planning to create is formed by:
− A GIS repository based on an OpenSource WebGIS
− A 3D Models repository based on OSG, PhP and
PostgreSQL
− A plug-in viewer for Internet Explorer for .ive (and .txp)
formats, and either a stand alone application fot other
browsers.
− An editing client with the same functions of the viewer and
some added functions which allow a user to set preferred
points of view or paths or to modify some aspects of the
landscape, adding new buildings or trees in geographical
position, taking them from the repositories.
− A server component to which is demanded the ….. of
distribution of data recalled by the viewer client and to
accept and validate the insertion and variation requests
produced by the editing client
− A rebuilding tool (batch) that, since the beginning,
periodically and on demand, activates a terrain regeneration procedure in order to apply the modified
elements. Some adjustments would need a longer regeneration time (as in the case of modification of the
DEM or of an aerial image that would request a complete
re-computation of the entire terrain model), compared to
other (such in the case of added trees or models at a certain
point).
Bateson G., 1979, Mind and Nature. A Necessary Unit, Dutton,
New York.
Camporesi C., Generazione di paesaggi tridimensionali. Un
approccio OpenSource per applicazioni real-time e web-based,
dissertation of univ. of Bologna, Dept. of Computer Science
(Prof. G. Casciola)
Calori L., Guidazzoli A., Forte M., 3D Virtual scientific
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Calori L., Diamanti T., Guidazzoli A., Liguori M.C., Mauri
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Fig.5 Access and Editing Tool
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ACKNOWLEDGEMENTS
Partner of the Appia Antica Project: CNR-ITABC, Istituto per
le Tecnologie Applicate ai Beni Culturali (Maurizio Forte,
Paolo Salonia coordinators); Archaeological Superintendence
of Roma municipality (coord. Paolo Grassi, Antonio Mucci,
Luca Sasso D'Elia); Italian Archaeological Superintendence
(Dott.sa Paris); CINECA Visit Lab: Cooperation on
OpenSource tools for the reconstruction and visualisation of
archaeological landscape.
Partners of the Certosa Project: Bologna municipality (M.
Felicori, C. Borgatti, M.C. Liguori, R. Martorelli, M.Bacchini,
N.S. Onofri, M. Lodi); CINECA (A. Guidazzoli, A. Mauri, F.
Delliponti, L. Calori, T. Diamanti); CNR ITABC (S. Pescarin);
HERA (M.Gaeta, R. Zanetti); Istituto Parri: (L . Alessandrini,
L. Cigognetti, C. Crupi); Archaeological Museum (C. Morigi
Govi, M. Marchesi)
A particular thank to Silvano Imboden (CINECA), Carlo
Camporesi (UNIV. of Bologna) and Marcello Morgotti
(CINECA).