Data Collection and Management for Stratigraphic Analysis

of Upstanding Structures

Elisabetta Donadio

and Antonia Spanò

Politecnico di Torino – DAD (Architecture and Design Dept), viale Mattioli, 39, 10125 Torino, Italy

{elisabetta.donadio, antonia.spano}@polito.it

Keywords: GIS, Masonries, Stratigraphy, Cultural Heritage, TLS, SfM.

Abstract: Stratigraphic analysis, used in principle for study of archaeological excavation, has been adapted and ap-

plied to upstanding structures with the same aim to reconstruct a building’s history. Stratigraphy, as well as

data excavation management, has found a useful and versatile tool in geographic information systems

(GISs). Such systems allow support of this kind of analysis, which is mainly related to the reconstruction of

the chronological sequence, statistical analysis, and their representation. This paper examines the process

that leads to the production of information and storage in a GIS, applicable for the management of the stra-

tigraphy of an upstanding structure. This process involves data acquisition, processing, 3D modelling, 2D

representation, graphical entities, and their topological relationships, determinations, and representations.

We also touch on the relationship between 3D GIS and 2D GIS; even if complex 3D archives are currently

achievable, from another point of view it can be also useful for carrying out a 2D workflow aiming at

achieving sharable guidelines that are valuable for specialists in Cultural Heritage conservation.

1 INTRODUCTION

The widespread use of information and communica-

tion technology (ICT) has radically improved the

availability of spatial information over the Internet,

and GIS tools have became powerful instruments to

perform complex analyses both on thematic and

geometric content.

Cultural heritage documentation is a field where

GIS applications have ensued general improve-

ments, also arisen from the increasing application of

GIS to urban cartography and the consequential

requirement to handle 3D representation.

In recent years, many proposals and ad hoc solu-

tions for digital documentation systems based on

GIS tools have been aimed at cultural assets (two

example among others: Apollonio et al., (2012) and

Katsianis (2008).

The GIS tools played a relevant role, first in the

archaeological field since they enable management

and analysis of a large amount of data according to

basic assumptions used by archaeologists for collect-

ing and managing site or ancient building infor-

mation. Moreover, archaeological practices pay

close attention to the spatial components of archaeo-

logical data. The reconstruction of past event or site

changes is initiated through reading and storing of

recognisable evidence related to the landscape in

which they are discovered. Effectively, the great

esteem for GIS tools has led to many disciplinary

considerations linked to archaeological science and

experiences (Scollar, 1999; Wheatley and Gillings,

2002).

In the last two decades, the community devoted

to CH protection has shown an interest in new tech-

nologies of data acquisition and management. In this

context, particularly GIS use has taken root.

This phenomenon is not unanticipated, since

some keywords or concepts included in international

conventions concerning the protection of the world

heritage (UNESCO, 1972, and later) are appropriate

for use with GIS tools.

The knowledge of the extent and the state of CH

in a region is related to the ability of managing geo-

graphical locations. The involvement of many spe-

cialists belonging to different fields of studies and

generally of stakeholders

active in CH protection

plans means that many different kinds of data must

be collected, produced, and stored. The ability to

connect diverse databases and to manage the tem-

poral dimensions are remarkable GIS skills. The GIS

tools are also widely used in CH documentation for

technical reasons; orthoimages and Digital Elevation

Models are easily managed and are increasingly

Donadio E. and Spanò A..

Data Collection and Management for Stratigraphic Analysis of Upstanding Structures.

DOI: 10.5220/0005470200340039

In Proceedings of the 1st International Conference on Geographical Information Systems Theory, Applications and Management (GISTAM-2015), pages

34-39

ISBN: 978-989-758-099-4

 2015 SCITEPRESS (Science and Technology Publications, Lda.)

used in built heritage applications.

Orthoimages, which are processed from terrestri-

al laser scanning (TLS) and/or from digital photo-

grammetry techniques, represent a particularly fa-

vourable representation for different specialists since

they include both metric and radiometric values.

Moreover, archaeologists or other non-experts in

survey techniques are autonomously able to extract

data from such orthographic building representations.

2 GOALS AND OPEN ISSUES IN

THE WORKFLOW OF DATA

ARRANGING FOR

STRATIGRAPHIC ANALYSIS

There are three main necessary phases for collecting

data for a stratigraphic analysis of an upstanding

structure. In the first phase, we need to choose the

method for data acquisition and process, in order to

obtain 3D models and orthoimages. In the second

phase, we need to make the survey results available

in a spatial data structure and format properly for

GIS management. To do this, we frequently need

data digitisation.

In the third phase, we must organise graphical

datasets and all other information. To make spatial

data available for queries and visualisation in con-

nection with other archaeological, technological, or

historical information, it is necessary to design a

model that identifies a correspondence between

spatial features and conceptual model data. The

issue of this operation is related to the necessity of

matching a structure based on topology with a struc-

ture that conforms to the geometric representation of

the architectural structure. Therefore, the generated

geometric entities must be compliant with topologi-

cal data structures.

This task, representing constructive or restoration

phases of buildings or sites, is usually performed to

fulfil chronological plans and is widely used by the

users community (e.g., Semeraro et al., 2012;

Bortolotti et al., 2013).

In this paper, we favour the first two phases;

therefore, some methods are discussed in the next

paragraphs.

2.1 Terrestrial Laser Scanner (TLS)

and Structure-from-Motion (SfM)

Techniques

Today, it is well accepted that a 3D model of data

derived from a digital survey using both active and

passive sensors is more rapid and provides more

details than using other survey systems. These mod-

els enable obtaining very useful shape documentation

and thematic characterisations that are more sustainable

in terms of cost and the amount of available information.

However, when comparing image-based techniques with

laser scanning, the former have a better chance for low

cost equipment and tools.

Recent digital photogrammetric software uses algo-

rithms derived from the computer vision community;

they take advantage of Structure-from-motion (SfM)

tools that enable estimated 3D positions of points repre-

sented in multiple images. Such systems can provide the

reconstruction of objects’ shapes and points’ positions

(Lowe, 2004).

Many other image-matching techniques have been

developed earlier than SfM, such as area-based matching

and feature-based matching, in order to solve the tie

points (TPs) extraction; after that phase, epipolar geome-

try is used to process internal and external orientation

and to create dense points clouds.

Section profiles or orthophotos are comparable

for metric accuracy (Chiabrando and Spanò, 2013)

and can be extracted to measure buildings, to exam-

ine safety conditions, and for deriving proper infor-

mation for stratigraphic analysis.

2.2 Features Extraction and

Automation in Digitising

Usually, some editing efforts are implemented in 3D

models or orthoimages generation in order to digitise

surveyed objects.

Architectural and archaeological fields usually

derive drawings after the measuring phase, and the

huge amount of information provided by accurate

and highly detailed 3D models make the manual

tracing well accepted.

Some commercial and open source tools offer

solutions to support and simplify this phase. Some

tools enable insertion of section planes cutting a

registered points cloud anywhere in the scene space.

In this way, it is possible to generate a mosaic of

images representing a parallel projection of the

cloud model on which extracts vectors.

Vector extraction, when manually performed, is

very time consuming, and even if this is a relevant

phase in reading assets, many automated or semi-

automated aiding tasks and algorithms can be taken

into account.

Sometimes a contours extraction tool applied on

the archaeological object surface, usually represent-

ed by a DEM, can be helpful as shown in Figure 1.

The success of this method depends on the re-

DataCollectionandManagementforStratigraphicAnalysisofUpstandingStructures

quired scale of analysis and is rarely proper for ma-

sonries analysis.

More often, the algorithms that are able to rec-

ognise the radiometric boundaries can be used to

process the vectorisation, usually by means of geo-

metric constraints, such as extension, shape, or

number of vertices for the recognised objects (Figure

2).

Figure 1: Vector sketches of the shape of evidence are

obtained with the help of a contours extraction task

(Costamagna et al., 2010).

A relevant request of process automation affects

many phases and aspects of CH documentation, and

occasionally some solutions are adapted from inno-

vative applications of other sectors.

The feature extraction and matching techniques

have traditionally been used in aerial photogramme-

try. Many operators, such as SIFT, are widely im-

plemented for automatic TP extraction and approxi-

mate digital surface model (DSM) generation (Lin-

gua et al., 2009).

Figure 2: An example of automatic vectorisation per-

formed by geometric constraints (tombs of Hierapolis

North necropolis (Spanò, 2008).

In order to automatically extract break-lines of a

surveyed object, some solutions foresee a continuous

exchange of information between Lidar and Photo-

grammetric techniques. The result is the complete

3D description of the object through break-lines

(Nex and Rinaudo, 2011).

An interesting tool, based on active contour and

fulfilled specifically for a stone-by-stone digitisation

aimed toward stratigraphical analysis, can be found

in Drap et al., (2007).

3 STRATIGRAPHIC ANALYSIS

REQUESTS: CHRONOLOGY

ISSUES

The use of archaeological methods in the study of

architecture aims to enrich the knowledge base,

since buildings show signs of transformation, resto-

ration, reconstruction, and demolition.

The application of the stratigraphic method to ar-

chaeology hails from Edward Harris’ experiences

dating back to the mid-twentieth century (Harris,

1989). The goal of archaeology is to define construc-

tion phases of the building (chronological sequenc-

es) within a relative chronology and subsequently,

their settings in an absolute chronology introducing

dates or periods.

The dating process starts with identification on a

3D or 2D representation of stratigraphic units (Unità

Stratigrafiche Murarie (USM)) intended as construc-

tive action with temporal autonomy.

There are two different types of stratigraphic

units: positive USM, if they result from a single

constructive action, and negative USM, if they result

from a removal action due to human action. Some

units are then defined as covering units if they cover

other units, such as plasters, paints, wall coverings,

and flooring.

Starting from this recognition, the analysis con-

tinues seeking temporal relationships between adja-

cent units and processing the stratigraphic sequenc-

es, consisting of all USM in temporal order. All of

these data are recorded in a data sheet. Likewise, for

the archaeological excavations, the USM are then

grouped into a construction phase to be able to better

study the history of the building.

The final step of a stratigraphic analysis consists

of the abstraction of the relationships between units

using a matrix diagram, conceived by Harris, which

is a system of representation of the stratigraphic

relationships that represent through a system of

symbols the chronological sequence of all actions,

constructive and destructive.

The stratigraphic method, which provides map-

ping of stratigraphic units on graphic representations

and their cataloguing in a descriptive database, re-

presents an example of a useful implementation of a

GISTAM2015-1stInternationalConferenceonGeographicalInformationSystemsTheory,ApplicationsandManagement

GIS. The advantage of this application is to exploit

the topological relationships resulting from vectori-

sation (and georeferencing) of each stratigraphic

unit.

4 CASE STUDY: THE NORTH

FRONT OF THE SANTA MARIA

CHURCH OF THE STAFFARDA

ABBEY

4.1 The Cistercian Staffarda Abbey

The Cistercian Staffarda Abbey is a monastery lo-

cated near Saluzzo in northwest Italy that was

founded in the XII century by Cistercian monks. The

abbey complex grew larger between XII-XIII centu-

ries with a gradual decline from that date onwards

(Rotunno, 2011). In 1750, the Holy See declared the

autonomous abbey’s role to be over, and the com-

plex was given to the Order of St. Maurice.

Due to the modifications over the centuries, the

monastery combines both Roman and Gothic archi-

tectural styles, and it includes the Santa Maria

Church, the cloister, other monastic rooms (the dor-

mitory, the refectory, etc.), the covered market, and

the guestrooms (Beltramo, 2010).

Much of the complex was built in red brick and

red sandstone. The church has a nave and two aisles,

and is a splendid example of Romanesque-Gothic

style.

Figure 3: 3D Model processed from LIDAR data.

The inside is austere, and the cross vault and the

pillars (all different from one another) are decorated

with alternating colours, which range from red to grey.

Externally, the overload of the roof led to the

construction in early medieval sites of the flying

buttresses that have improved but not solved the

problem. Currently, the monastery represents one of

the most important testimonies of medieval architec-

ture in Piedmont.

The stratigraphic analysis involved in the north

facade, particularly the three spans and the transept,

are characterised by many visible stratifications. For

example, the signs of demolition and filling of the

eighteenth-century chapels and some of their decora-

tions are still evident as well as the holes of their

coverage.

Figure 4: Holes on the masonries determined by a recent

restoration.

Figure 5: Zoom-in on an example of a chapel decoration.

4.2 The Stratigraphic Analysis

The analysis has been carried out recognising and

contouring units on orthoimages generated from the

3D point laser cloud. This phase led to the recogni-

tion of 74 positive USM, 22 negative USM, and 115

covering units.

Figure 6: Attribute data tables implemented in GIS.

DataCollectionandManagementforStratigraphicAnalysisofUpstandingStructures

The next step consisted of the identification of

the temporal relationship between each unit and its

adjacent units. In order to archive and link this kind

of descriptive information, an attribute database has

been created.

Figure 7: Example of a data thematisation: in green posi-

tive USM, in red negative USM, in yellow covering units.

In 2D or 2.5 representation GIS projects, the co-

ordinate system cannot be the original system of the

laser model that coincides with the topographical

reference system. Necessarily, the graphical vector

dataset representing the front façade is projected

onto a vertical plane measured by xy coordinates.

The original coordinate system must be shifted and

turned for each face of the building that is analysed

and represented; corresponding features in different

drawing projections that represent the same real

elements can be connected by a relationship.

Figure 8: Result of a select by attribute query about the

218 USM. The system allows highlighting all the USM

that have a relationship with it and to thematise features

based on the type of relationships they have.

The implementation of features representing

USMs and the related chronological relationships

allow generation of several useful thematisations.

It also allows querying the data by location or at-

tributes, depending whether it is proper to take ad-

vantage of topological relationships or when it is

better to use attribute data.

Figure 9: Harris matrix processed using GIS attribute

selection.

5 CONCLUSIONS AND

PERSPECTIVES

Despite the fact that this sketchy experience is based

on 2D representation GIS, it shows two evident

positive points. The first is that a powerful analysis

for a CH conservation plan is achievable through

well-known functionalities among GIS users. Later,

but even more relevant, the use of many graphical

frameworks, each representing a drawing projection

of the building (plan, fronts, and cross sections),

offer the chance to manage the entire complex of the

building. Architects and archaeologists are used to

using different 2D representations in studies of 3D

spaces or objects. Further, by means of exploiting

the capability to connect different features represent-

ing the same real elements, they can enhance their

analyses.

In addition to the easy to use tools, another profitable

GISTAM2015-1stInternationalConferenceonGeographicalInformationSystemsTheory,ApplicationsandManagement

issue for the CH documentation community is the low

cost systems. The increasingly common use of open

source tools, such as PostGis, is placed side-by-side to

commercial tools, such as the popular ESRI products

even among the CH preservation plans.

The development of 3D GIS (i.e., systems where

the same importance to the (x,y,z) coordinates is

assigned) is attractive in the CH conservation com-

munity. The 3D management, both in data visualisa-

tion operations and in data retrieving or editing

operations, offers the achievement of specialised

analyses.

In some cases, open source framework and ad-

vanced ad hoc systems for some relevant contexts

are used (e.g., Coralini et al., 2010)

A very interesting specialised system has been

developed for the Shawbak project. A 3D GIS al-

lows management of both photogrammetric models

and 3D shape restitution of built structures in spatial

archive as well as processing and automatic visuali-

sation of the Harris matrix with clusterisation of

geometric elements (Drap et al., 2012)

A section of the scientific community, which has

been working on information systems for CH preserva-

tion, started to investigate the benefits of switching from

a 3D content model to historic building information

modelling (HBIM) to support conservation plans (Oreni

et al., 2013). Furthermore, studies comparing the ad-

vantages and disadvantages of both BIM and GIS ap-

proaches are available (Saygi et al., 2013).

In both cases, BIM or GIS adoption, there is the

need to enhance the automatic digitisation tools

starting from orthoimages and points models, since

only more sustainable and easily approachable pro-

cedures can represent an effective strategy for basic

and common use in CH conservation plans.

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DataCollectionandManagementforStratigraphicAnalysisofUpstandingStructures