=Paper=
{{Paper
|id=Vol-1352/paper6
|storemode=property
|title=Digital Representation Platform and Multi-Scale Representation for a Multidisciplinary Knowledge of Some UNESCO World Heritage Sites in Italy
|pdfUrl=https://ceur-ws.org/Vol-1352/paper6.pdf
|volume=Vol-1352
|dblpUrl=https://dblp.org/rec/conf/iui/Masi15
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==Digital Representation Platform and Multi-Scale Representation for a Multidisciplinary Knowledge of Some UNESCO World Heritage Sites in Italy==
https://ceur-ws.org/Vol-1352/paper6.pdf
Digital Representation Platform and Multi-Scale
Representation for a Multidisciplinary Knowledge of Some
UNESCO World Heritage Sites in Italy
Alessandro De Masi
Department of Architecture,
Built environment and
Construction engineering, Milan
Polytechnic, II School of
Architecture (ABC)
Via Durando 10, 20158 Milan,
alessandro.demasi@unina.it,
alessandro.demasi@polimi.it
ABSTRACT activities of the decision-making process for heritage
The paper describes reading criteria for the conservation management [4]. Conservation, being an
interpretation/documentation, integrated systems of digital ongoing activity, can be best described as a cyclical
technologies and 2D/3D digitization of Cultural Heritage process, with heritage information being the knowledge
(CH) and the procedures followed by Digital base to which everyone dealing with the heritage
Representation Platform (DRP) promotes through contributes and from which everyone retrieves information.
integrated digital survey for CH in Milan and Trento as a Without such a knowledge base collecting and
case study of the research on the integration of new disseminating information at all stages, the conservation
technologies to obtain 3D multi-scale representation process is without reference [5]. The DRP offer the
architectures. The study from the methodological point of possibility of obtaining new products not only in the
view has made use of the identification of levels of study surveying activity but also in representation, visualization,
differentiated, each of which is capable of identifying digital information and communications technologies with
categories. powerful instruments for multi-faceted analysis.
Additionally, it offers a wide range of applications for
Author Keywords collecting and processing historical data, monitoring of
Digital Representation Platform, Multi-Scale monuments and creating interactive information networks.
Representations, 3DCM, 3D Digitization Methodologies, Moreover, the present research project it is placed between
Heritage Recording the targets to explore the possibility of integrated digital
survey and multi-scale representation. I have made 3D
1. INTRODUCTION AND OBJECTIVES models of both the current status (geometric model) that
In recent years, digital heritage has begun to transform the support the analysis of the various stakeholders in order to
process of re-creating and understanding the past [1]. Infact, identify guidelines for the relief aimed at the realization of
the purpose of the ICOMOS Charter for Interpretation and multi-scale models of architectural sites. Today new
Presentation of CH Sites is to define the basic principles of opportunities for an integrated management of data are
Interpretation and Presentation as essential components of given by multi-resolution models, that can be employed for
heritage conservation efforts and as a means of enhancing different scale of representation. It was identified a
public appreciation and understanding of CH sites [2]. The methodology for reading that can return a survey aimed at
paper describes reading criteria for the evaluating changes induced by simultaneity through the
interpretation/documentation, integrated systems of digital decomposition of multi-scale representation of the parties
technologies and 2D/3D digitization of CH and the examined. Here I report the results of the research on most
procedures followed by DRP [3] through integrated digital significant architectural buildings of Milan and Trento.
survey. The DRP is meant to be particularly useful to
heritage managers who are developing recording, 2. LINE OF RESEARCH METHODOLOGY
documentation, and information management strategies for I identified relief guidelines aimed at the realization of
territories, sites, monuments. Recording, documentation, architectural sites multi-scale models. This was made
and information management are among the central
possible by the geo-referencing process consisting in the
insertion of local systems in less local systems. Therefore
the relation between the uncertainty of the model (derived
from the uncertainty of the measurements), and
simplification of the model (derived from selecting and
transmitting only some geometric information considered
essential to the description of the object on a certain scale)
has been taken into account. The research was articulated
according to the DRP of the architectural and the urban
landscape, consisting of a set of cultural, geometric,
morphological and dimensional knowledge for the creation
of a 3D digital model implementable with multidisciplinary
themes. The DRP improves current policies and standards
and is based by: 1- heritage information with integrated
activities of recording, documentation, and information
management to acquire knowledge, understand values,
promote the interest and involvement of scholars and ensure
long-term maintenance and conservation of heritage places.
2- Information management with the process of finding,
cataloguing and sharing information by making it
accessible to potential users now and in the future; 3-
Recording with the acquisition of new information deriving
from all activities on a heritage asset, including heritage
recording, research and investigation, conservation, use and
management, and maintenance and monitoring. (Fig.1) The
benefits of integrated digital survey describing the physical
configuration of sites and their physical condition at known
points in time fall into two broad areas: 1-conservation
planning and management; 2-provision of a permanent
archival record. These were the steps followed: 1- Visual
frameworks in the urban space; 2- Criteria of heritage
significance and principles of evaluation of CH assets. 3-
Study of current methods of 2D/3D digitization intended
and Open Source for CH preservation. 4- Study of the relief Figure 1: The use and flow of heritage information and
procedures with integrated laser scanning and Heritage Recorders (Brizard, Derde, Silberman, 2007, Basic
Guidelines for Cultural Heritage).
photogrammetry. About the relief of the elevated parts,
scanning and relief stance optimization were considered. 5- contemporary signs. The relief and the representation of the
Study of the relief integration methods applied to the plan LS return information classifiable in a uniformed manner
and the elevated parts in order to define a one-3D system. from a spatial, a functional, and a thematic point of view.
This was to identify the invariant with respect to the scale The guidelines on criteria and conditions for evaluation of
of representation in the geometry of the object and then CH Assets were following: 1- historic and aesthetic
proceed to the geo-referencing. 6- Study of best practices significance. Is related to its style, technical excellence,
for the realization of 3D models that are mapped to beauty, quality of design and execution; 2- Scientific or
different nominal scales and with different levels of detail. research significance; 3- Social and spiritual significance.
7- Study of scale changes in the individual models (site, For this reason, the survey also was based on the following
architecture, details) with simplifications based on the criteria for complex representation: 1-Intrinsic significance
selection and activation of geometric information from (Authenticity, Extent/Completeness, Integrity, Continuity
different nominal scales. 8- Accurate documentation of of use/demonstration, Corpus of evidence/study; 2 -
each cultural object, encouraging an integrated Contextual significance (Rarity, Representativeness
interdisciplinary approach. 8- Study of Open Source tools /Uniqueness, Diversity, Physical context, Threat/fragility;
and software for CH fruition and conservation. From a 3- Associative significance (Historic interest and
methodological perspective, the identification of Levels of association, Aesthetic attributes. The principles of
Study (LS) has allowed me to identify categories of evaluation of CH assets is carried out in accordance with: 1-
dimensional, constructive, formal and cultural values. Scientific knowledge and experience in the field to which
Therefore, I started from the existing data collection the cultural asset belongs; 2-Available data and
organized by categories and subcategories, to understand documentation on the asset (inventory, survey, study); 3-
the current relationship between identity signs and Results of additional research specifically;
connection/relation with other categories of asset, or object are described in context of one of the LODs [12].
persons, communities and regions [6]. (Fig. 2)
3. MODEL AND CHARACTERISTICS OF MULTI-SCALE
REPRESENTATIONS
The goal of multi-scale representations is to provide several
representations where each representation is adapted to a
different information density. Moreover, the multi-scale
representations are representations of a given model in
several degrees of detail [7]. Typically one primary
representation is used to derive secondary representations
with adapted scale as needed. In practice multiple discrete
representations are typically prepared and stored in
advance. An important characteristic of multi-scale
representation is the similarity between the representations
and the described subject, where similarity is defined
depending on the purpose. According to defined by the
Object Management Group (OMG), a model captures a
view of a system and describes those aspects of the system
at the appropriate level of detail. Ideally the required variant
can be generated on-the-fly for a continuous range of
resolution requirements. To overcome the problem of Figure 2: The CityGML specification contains these examples
mismatch between required and prepared representation, to illustrate typical use of its five consecutive levels of detail -
the representation with the closest resolution is used. In LOD - (Gröger et al., 2008).
their simplest form, multi-scale representations form a
ordered, linear sequence of representations R0,R1, ...,Rn, These were the LODs followed: 1- LOD-0 used for regional
where R0 has the highest detail and Rn the lowest. scale and contains a 2.5D terrain model with a surface
Frequently, multi-scale representations are organized texture applied. 2- LOD-1 contains prismatic block building
hierarchically. Preprocessing a primary representation in a models with flat roofs and no façade textures. 3- LOD-2
hierarchical way allows one to follow a divide-and-conquer contains buildings with differentiated roofs as well as
approach, i.e., to split the problem into smaller portions and thematically and geometrically differentiated surfaces,
process them independently [8]. In 3D computer graphics, including textures. Vegetation objects may be included. 4-
level of detail (LOD) modeling represents a fundamental LOD-3 contains highly detailed architectural buildings with
principle LOD modeling enables interactive rendering of high resolution textures as well as highly detailed
data sets that otherwise could not be rendered interactively vegetation and transportation objects. 4- LOD-4 adds
or could not be rendered at all, as their size exceeds main or interior structures to buildings, such as stairs or furnitures
graphics memory, or processing power is too low. The [13]. The CityGML standard is flexible with multiple
LOD models are models with low polygon count either representations of a 3DCM. Infact, 3DCM should be used:
created by hand or derived automatically from a primary 1- Combinations of different LOD representations of
model [9]. To avoid disturbing popping artifacts when buildings and the relief model within the same scene is
switching, geomorph techniques perform a smooth possible. 2- CityGML introduces the concept of the terrain
geometric interpolation between different LOD models intersection curve (TIC), which describes the interface
[10]. between a feature. It is a applications can locally adapt the
terrain model to embed the feature. According to defined by
3.1. From knowledge to Complex Representation: Multi-Scale Kada (2005) suggests reconstruction of a building model
Representations of Virtual 3D City Models for CH and Urban using half spaces. For each wall face of the original model,
Space
the algorithm creates a plane and a related buffer. Starting
According to defined by the international CityGML
with the face with the largest area, the algorithm merges
standard (see you Open Geospatial Consortium) a virtual
faces within a given maximum distance to the current face’s
3DCM is the digital representation of urban space that
buffer, adapting the plane’s parameters and leading to a
describes geometrical, topological and appearance
smaller number of planes. The final set of planes is used to
properties of its components with an explicit level of detail
create a cell decomposition of the building. Rau et al.
(LOD). In general, a 3DCM serves as an integration
(2006), suggests an approach working on building models
platform for multiple facets of an urban information space.
comprised of prismatic shapes with sloped roof structures.
Visualization is an important part of many applications of
First, the roofs are flattened and adjacent polyhedrons are
3DCMs [11]. CityGML defines for city objects five LODs
merged if their height difference is smaller than a given
and requires that geometric and thematic aspects of a city
feature resolution, yielding 2.5D shapes. Moreover, Forberg
(2004) introduces another scale-space based on parallelism
to generalize earlier findings and combine characteristics of
both morphological and curvature space operations. The
algorithm identifies parallel faces of the model and, starting
with the smallest distance, moves faces towards each other
so that they share the same plane. The moved faces result in
merging building parts, removal of protrusions or
adjustment [14]. In the approach of Fan et al. (2009) is
directed at generalizing CityGML LOD-3 building models
where the polygons belonging to one wall are projected to
the farthest of its polygons’ planes; polygons that are not
parallel or coplanar are discarded. In his thesis Fan (2010)
suggests another approach for the computation of CityGML
LOD-2 building models with the building footprint is
simplified using rules from Staufenbiel (1973), extended by
rules to handle non-orthogonal curvature. Moreover. the
roof geometry is generalized by individual polygons that
are simplified using the same rules. Third, the generalized
footprint is extruded until it meets the generalized roof
geometry. Coors (2001) applies an adapted surface
simplification algorithm (Garland and Heckbert, 1997) to
simplify single buildings. Introducing dominance values on
important parts of the building. The simplification
algorithm is adapted to conserve these parts while
simplifying geometric complexity of the remaining model
[15].
3.1.1 Cell-Based Generalization
Cell-based generalization another technique to create
representations of 3DCMs that are focused on giving a Figure 3: Buildings models are aggregated using boxes stored
quick overview about the general structures of the urban in an R-tree for efficient network transfer and visualization.
space and is intended to facilitate multiple purposes. Landmark buildings such as churches can be presented with a
According to defined by Lynch (1960), who describes five higher detail using dominance values (Coors, 2003).
major elements forming a city’s mental image: paths, edges, removal, aggregation of adjacent buildings by edge
districts, nodes, and landmarks distinguishable objects used removal, and aggregation of non-connected buildings
for orientation. Therefore, I address this by using street guided by a cost function [17]. Designing landmarks in
network, coast lines, as well as non-building areas of a virtual 3D environments such as 3DCMs therefore can
3DCM to create cell blocks. I assume that block cells can facilitate navigation and the acquisition of spatial
represent individual buildings and monuments abstractly. knowledge [18]. Local landmarks and different levels of
The cell blocks are further shaped by computational global landmarks can be differentiated by the size of their
geometry operations and enhanced by landmark buildings, reference region. For higher LOA representations, I use a
which are maintained in the visualization. 3D building different technique to identify landmarks. The goal is to
shapes are included, rendered as transparent shapes and reduce the number of landmarks, while keeping important
with perspective projection in real-time. The visualization ones and maintaining an even spatial distribution. In the
aims at adaptation to the scale: with increasing scale, resulting landmark hierarchy, the number of landmark
buildings are first represented as footprints, then as oblique buildings is steadily reduced in subsequent layers of the
3D shapes with reduced height, then with their full height. hierarchy. (Fig. 4)
Secondly, photo-realistic perspective views of 3DCMs –
either real-time renderings or oblique photographic imagery 3.1.2 Creating Building Representations
– are enhanced with text, icons, and rendered vector data We have two types of building representations: high detail
[16]. (Fig. 3) The technique of Royan et al. (2005) 3D geometry stored for single landmark buildings and 2.5D
processes 3DCMs containing 2.5D building models to get a cell blocks. Whilst the former is directly integrated into the
hierarchical representation usable for progressive scene, the latter requires the creation of 3D geometry by
transmission. The algorithm applies simplification extruding their polygonal footprints. The extrusion shape
operations to the 3DCM: footprint simplification by vertex consists of wall geometry and planar roof geometry. We use
Figure 5: Schematic and 3D example of a junction after
(right) processing of road segments, landmark buildings can
be emphasized by scaling them according to their importance
for navigation and orientation, enhancing the skyline.
of an object and extracting the 3D geometry by monitoring
the deformations of each pattern [25]. The SL systems that
are able to capture 3D surfaces in real-time by increasing
the speed of projection patterns and capturing algorithms
[26]. The Image-Based methods involve stereo calibration,
feature extraction, feature correspondence analysis and
depth computation based on corresponding points can be
considered as the passive version of SL. Photogrammetry is
another popular active method that is used to determine the
2D and 3D geometric properties. It can be described as the
determination of camera interior and exterior orientation
parameters, as well as the determination of the 3D
coordinates of points on the content of the images [27].
Open photogrammetric software solutions are able to
Figure 4: For increasingly abstract representations, the
perform tasks such as high accuracy measurements, camera
algorithm creates increasingly large block cells with
decreasing numbers of landmark buildings (small Berlin epipolar geometry computations and textured map 3D mesh
dataset). The definitive version of these images can be found at extraction. Recently have been introduced semi-automated
(Glander and Döllner, 2009). image-based methods such as Structure-From-Motion
(SFM) and Dense Multi-View 3D Reconstruction (DMVR)
the computed LOA representations in a focus+context methods. The SFM-DMVR (algorithms from unordered
scenario by applying generalization lenses [19]. (Fig. 5) image collections) attempts to reconstruct depth from a
number of unordered images that depict a static scene or an
4. 3D DIGITIZATION METHODOLOGIES object from arbitrary viewpoints. The method mainly uses
At present there is a significant variety of 3D acquisition the corresponding features, which are shared between
methodologies. Those can be classified to contact and different images that depict overlapping areas, to calculate
noncontact 3D scanners [20]. Contact systems are not the intrinsic and extrinsic parameters of the camera [28].
popular in the CH domain due to the fragile nature of Eos Systems Inc. offers PhotoModeler Scanner software to
artefacts. In contrast, non-contact systems have been used perform tasks such as reconstruct the content of an image
during the last decade in many CH digitization project with collection in 3D dense point cloud that can be converted to
success [21]. Non-contact systems are divided into active a triangulated 3D mesh of different densities. In the same
and passive. The Laser Triangulation (LT) active direction, Agisoft offers PhotoScan to perform high quality
acquisition method is based on a system with a laser source 3D reconstructions, orthophotographs, digital elevation
and an optical detector with the depth is computed by using models and georeferenced 3D models.
the triangulation principle. The acquisition system is able to
4.1 Case Studies: Digization of Cultural Heritage
capture both geometry and colour using the same composite
The cases study are a attempt for the 3D digitization and
laser beam while being unaffected by both ambient light
representation of two CH in Milan, Italy. There are no
and shadows [22]. The Time-Of-Flight (TOF) active
buildings around the monuments and they are considered an
method is used for the 3D digitization of architectural
open access monuments. The 3D digitization of the
ensembles. The method relies on a laser range finder which
monuments could be performed using photogrammetric
is used to detect the distance of a surface by timing the
survey with multi-image 3D reconstruction. The position of
round-trip time of a light pulse [23]. For large measuring
the two monuments allow the selection of viewpoints
ranges TOF systems provide excellent results [24]. The
for photoshooting around the model. I used Agisoft
Structured Light (SL) is another popular active method that
PhotoScan as software solution for the production of digital
is based on projecting a sequence of different density
3D replicas of monuments. Infact, the process of capturing
bidimensional patterns of non-coherent light on the surface
require temporary scaffolding for the image-based
methodologies. I need to create a complete exterior
3D model of a monument using terrestrial photography.
Moreover, I compare the 3D mesh produced by the SFM-
DMVR software against the data I captured using terrestrial
3D laser scanning and total station surveying. For the
terrestrial photo shooting session a DSLR Nikon D40 (18-
55 mm lens) has been used with distance of the camera
from the monument’s surface was estimated at 5 meters.
The range scans covered both high and low curvature areas
that were enough for validating the quality of the data
produced by SFM-DMVR software [29]. A total of 400
photographs has been used for the 3D model of the
monument 300 and a total of 24 points were measured
using a Topcon GPT-3005N total station. The SFM-DMVR
software (Version 0.8.5) has been used for this case study.
(Fig. 6)
4.2 Heritage Recording and 3D Modeling with
Photogrammetry and 3D Scanning
The aspects of the evolution of CH can be documented by
the combined use of laser scanner and techniques of photo-
scanning. (Fig. 7) In fact, the photogrammetry has had the
task of providing the deliverables on which to base the
reading multi-scale. Through geo-referencing, in the
process of surveying, which can identify the invariant with
respect to the different scales of representation in the
geometry of the objects. The network classification of sites
surveyed for buildings recorded in Milan was composed in
two schemes. The network was built with total station Leica
TCA, while the GPS and Leica GPS System 500 GPS1200.
The points of support for the relief photogrammetric were
detected with both topographic measurements (Leica
TCR1103 and TCRM 1103) from ground GPS. The GPS
survey was carried out with a long session for the
determination of the absolute coordinates of the points of
the main network, while for the determination of natural or
target points for the support photogrammetric has acquired
in RTK mode. The laser scanner used is the model of the
Riegl LMS-Z360i with integrated digital camera which
offers the opportunity to acquire not only the three points
needed to determine the coordinates X, Y, Z each point but
also to acquire even the RGB values corresponding to each
measured point. To obtain a dense DEM models of the
monuments of the site, you have done a total of 17 scans in
overview mode and detailed in the in the center of Milan,
and 13 in Trento, always in the two modes. The clouds
were aligned on the basis of support points and tie points
measured topographically distributed in the scanning area.
Figure 6: SS. Giovanni Battista e Paolo Church, Milan, Italy
The optimal value of 0.2 mm multiplied by the denominator
(architects Figini e Pollini). Image position around the Church
of the ratio allows you to fix a priori a pattern of and Reconstructed CH by Smooth Shaded Triangular Mesh
acquisitions in a manner very similar to the design of a and Vertex Painted Medium Quality Triangular Mesh.
photogrammetric survey, considering not only the overlap
between scans to ensure good alignment, but also a
distribution "pseudo-do-set" of points. The construction of a
3D-RGB digital model, obtained by some digital images of
a real model, makes possible to acquire not only geometric
data but also chromatic and thematic data. The data
acquisition phase with ZScan was obtained by simultaneous
acquisition of point of clouds and "photo-scanning" textures
based on an algorithm of tri-multifocal analysis of the
image. The latter, using coloured point of clouds, sees the
images as input of information being metrically and
chromatically valid in 3D coordinates of the points. The
resulting models were exported for the subsequent phases
of editing and generation of plans, sections, profiles,
contour lines, up to DEM (Digital Elevation Model). The
use of multi-level images, obtained with overlapped colored
filters, can return as a photometric light curve resulted from
the amount of absorbed light.
5. RESULTS AND CONCLUSION
In this paper different approaches to the acquisition and
visualisation of 3D information from images have been
examined. Moreover in this paper different approaches to
the 2D/3D digitisation, 3D data acquisition methodology,
3D data post-processing of 3D information from images
have been examined. I have to demonstrate that 3D
acquisition methodology play an important role at all scales
of research. 3D modeling should be intended as the
generation of structured 3D data from the surveyed
unstructured data and it consists of geometric and
appearance modeling. However, for large sites’3D
modeling, the best solution is the integration of image and
range data for document and preserve the landscape and
heritage as well as share and manage them. The RDP is
configured in this way as a resource to analyze the complex
reality of measuring the material aspects with socio-
economic mechanisms of perception of the quality of
living. In addition the RDP show the potential of modern
technologies of detecting, sharing and managing digital
information in order to preserve the CH. The recent
developments in image matching have demonstrated the
potential of photogrammetry to derive all the fine details of
an object with geometric results from a relatively small
number of images very similar to active sensors.
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