The geometric documentation of the Greek cultural heritage sites participating in the TRIQUETRA project

7
Cha alabos IOANNIDIS(*), Kimon PAPADIMITRIOU(**), Alexand os TOURTAS(**), So ia SOILE(*),
Fo is BOUREXIS(*), Panagio is TOKMAKIDIS(**), Kons an inos TOKMAKIDIS(**),
S yliani VERYKOKOU(*) & Ch yssy POTSIOU(*)
(*)Na ional Technical Uni e si y o A hens - School o Ru al, Su eying and Geoin o ma ics Enginee ing - Labo a o y o Pho og amme y - A hens, G eece
(**)A is o le Uni e si y o Thessaloniki - Facul y o Enginee ing - School o Ru al and Su eying Enginee ing -Labo a o y o Topog aphy - Thessaloniki, G eece
Co esponding au ho : cioannid@su ey.n ua.g
THE GEOMETRIC DOCUMENTATION OF THE GREEK CULTURAL HERITAGE SITES
PARTICIPATING IN THE TRIQUETRA PROJECT
ExTENDED AbSTRACT
I si i del pa imonio cul u ale, su scala gobale, sono a ischio a causa dei cambiamen i clima ici, dei p ocessi geologici e delle condizioni
ambien ali es eme, che po ano a una lo o g aduale deg adazione. La documen azione geome ica sis ema ica del nos o pa imonio cul u ale
è una p ocedu a ondamen ale che cos i uisce la base pe gli s o zi di conse azione e le misu e di mi igazione del ischio. P odo i o og am-
me ici di al issima p ecisione s olgono un uolo essenziale in ques i in e en i, g azie alle app esen azioni geome iche de aglia e dei si i
cul u ali, che suppo ano il moni o aggio a lungo e mine, la piani icazione della conse azione e s udi di alu azione del ischio mol o p ecisi.
U ilizzando modelli di mesh 3D, o omosaici e modelli digi ali di supe icie (DSM), ingegne i, conse a o i, ice ca o i e u i gli s akeholde s
in e essa i possono esamina e da icino lo s a o a uale dei si i cul u ali, ile a e e en uali cambiamen i nel empo (a condizione che siano
disponibili p odo i di documen azione geome ica passa a) e me e e in a o s a egie di conse azione mi a e.
Ques o a icolo p esen a la documen azione geome ica di e impo an i si i a cheologici in G ecia: Aegina Kolonna, la Ci à som-
me sa e il pa imonio cul u ale cos ie o di Epidau o An ica e il san ua io di Kalapodi. Ques i si i cos i uiscono i si i pilo a del pa imonio
cul u ale g eco del p oge o di ice ca eu opeo TRIQUETRA, essendo di g ande impo anza a cheologica e, allo s esso empo, espos i a
di e si ischi ambien ali, a cui e osione cos ie a, somme sione, danni da gelo e deg ado dei ma e iali. La documen azione è s a a eal-
izza a nell’ambi o del p oge o TRIQUETRA, il cui obie i o p incipale è a on a e i ischi lega i ai cambiamen i clima ici e ai pe icoli
na u ali che minacciano il pa imonio cul u ale, a a e so un se di a ezzi inno a i a e un sis ema di suppo o alle decisioni (DSS) pe
l’iden i icazione, la quan i icazione e la mi igazione dei ischi.
Pe documen a e ques i si i, è s a a impiega a una combinazione di ecniche o og amme iche. Ad Aegina Kolonna, sono s a e u ilizza e
la o og amme ia con d oni (UAV) e ilie i a e a pe documen a e il si o a cheologico e il paesaggio ci cos an e, semp e più in e essa i
dall’e osione cos ie a e dall’esposizione a sca i a lungo e mine. Nell’An ica Epidau o, il pa imonio cos ie o è s a o ile a o ami e ecniche
UAV LiDAR e basa e su immagini, men e i es i somme si della Ci à So ’acqua sono s a i egis a i usando o og amme ia subacquea e
ilie i con ecoscandaglio mul i-beam (MBES), a on ando ischi quali l’innalzamen o del li ello del ma e, la bio-e osione e le a i i à umane.
A Kalapodi, do e i danni da gelo app esen ano un ischio impo an e pe la s abili à s u u ale, sono s a i e e ua i ilie i a e a con ecniche
UAV LiDAR e basa e su immagini pe documen a e lo s a o del si o e suppo a e una piani icazione conse a i a ada a a al clima.
I se di da i accol i du an e ques e campagne sono s a i elabo a i u ilizzando wo k low o og amme ici consolida i, a cui il ma ching
di immagini, la icos uzione 3D ami e S uc u e om Mo ion (S M), la gene azione di nu ole di pun i dense, la icos uzione di supe ici
idimensionali, la mappa u a delle ex u e, la c eazione di modelli digi ali di supe icie (DSM) e o omosaici. I isul a i o og amme ici inali
app esen ano da i ondamen ali pe moni o a e i cambiamen i s u u ali, condu e analisi ambien ali e guida e le decisioni sulla ges ione dei
si i e le misu e di conse azione speci iche. Ques o s udio, insieme al la o o più ampio ealizza o nell’ambi o del p oge o TRIQUETRA,
dimos a quan o sia impo an e un’acquisizione con inua di da i e, sop a u o, una collabo azione in e disciplina e, pe ga an i e la p o ezione
dei si i del pa imonio cul u ale pe le u u e gene azioni. La usione dei isul a i p o enien i da di e se discipline, come opog a i, ingegne i
ci ili, geologi, ingegne i chimici, oceanog a i, me eo ologi e clima ologi, è essenziale pe c ea e un quad o sos enibile ol o a sal agua da e i
si i a cheologici, specialmen e in un’epoca di c escen i s ide lega e ai cambiamen i clima ici.
I alian Jou nal o Enginee ing Geology and En i onmen
www.ijege.uni oma1.i
IJEGE, Special Issue 1 (2025): 7-24, DOI: 10.4408/IJEGE.2025-01.S-01
E-ISSN 2035-5688 | ISSN 1825-6635 / ©Au ho (s)
8 I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue 1 (2025) www.ijege.uni oma1.i
C. IOANNIDIS, K. PAPADIMITRIOU, A. TOURTAS, S. SOILE, F. bOURExIS, P. TOKMAKIDIS, K. TOKMAKIDIS, S. VERYKOKOU & C. POTSIOU
AbSTRACT
In he ligh o h ea s including clima e change, geological
deg ada ion and ex eme wea he condi ions, he geome ic
documen a ion o cul u al he i age si es plays a c ucial ole in hei
p ese a ion. Pho og amme ic echniques enable he p oduc ion o
highly accu a e 3D models, o hoimages, and digi al su ace models
(DSMs), which acili a e bo h si e moni o ing and conse a ion
planning. This a icle p esen s he pho og amme ic documen a ion
o h ee a chaeological si es in G eece, namely, he a chaeological
si e o Aegina Kolonna, he Sunken Ci y and he coas al cul u al
he i age o Ancien Epidau us, as well as he sanc ua y o
Kalapodi. The geome ic documen a ion o all h ee si es was
conduc ed wi hin he amewo k o he TRIQUETRA EU- unded
p ojec , h ough g ound su eys and UAV-based pho og amme ic
echniques, ei he independen ly o in combina ion wi h unde wa e
pho og amme y wo k lows, in o de o cap u e he geome y o
he cul u al he i age si es and hei su ounding en i onmen s. The
p oduced esul s include 3D dense poin clouds, 3D ex u ed mesh
models, DSMs and high- esolu ion o homosaics. The gene a ed
da ase s suppo de ailed s uc u al assessmen s, ulne abili y
analyses and isk assessmen s udies, p o iding a undamen al
basis o p o ec ion e o s o he a chaeological si es o in e es .
Keywo ds: geome ic documen a ion, 3D model, cul u al he i age,
UAV-based pho og amme y, unde wa e pho og amme y, LiDAR
INTRODUCTION
The geome ic documen a ion o cul u al he i age si es is a
undamen al p ocess o hei p ese a ion. In he ace o h ea s
such as clima e change, geological deg ada ion o ex eme wa e /
snow/ice, accu a e pho og amme ic p oduc s, like 3D models,
o hoimages and digi al e ain/su ace models (DTMs/DSMs) o
cul u al he i age si es play a i al ole o hei conse a ion and
moni o ing. Ad anced pho og amme ic echniques can se e as
a c i ical ool o cap u ing p ecise eco ds o cul u al he i age
si es, acili a ing conse a ion planning and p omo ing public
awa eness and engagemen wi h ou cul u al he i age.
This pape ocuses on he geome ic documen a ion o
h ee p ominen a chaeological si es in G eece, as pa o he
TRIQUETRA p ojec : in Aegina, Epidau us and Kalapodi.
TRIQUETRA is a esea ch p ojec unded by he Eu opean Union,
ha aims o add ess clima e change isks and na u al haza ds
h ea ening cul u al he i age, h ough an inno a i e oolbox o
isk iden i ica ion, quan i ica ion and mi iga ion (Ioannidis e alii,
2023). I s p ima y objec i es include he c ea ion o a knowledge
base pla o m o clima e impac s and mi iga ion measu es, he
de elopmen o sys ema ic app oaches o assessing eme ging
isks, ad ancing echnologies o quan i ying h ea s and
aising public awa eness o in ol e ci izens in cul u al he i age
p ese a ion. Key ac i i ies o he TRIQUETRA p ojec in ol e
a new lash LiDAR o 3D mapping o unde wa e cul u al
he i age and e osion moni o ing, no el spec oscopic senso s
o wa e quali y es ima ion, he e inemen o clima e and isk
quan i ica ion models and he in eg a ion o emo e sensing
echniques. The basic ou come o he p ojec is he de elopmen
o a mul i-haza d impac assessmen pla o m, which unc ions as
a decision suppo sys em (DSS). The TRIQUETRA p ojec was
launched in Janua y 2023 and will conclude in Decembe 2025,
including alida ion es ing a eigh pilo si es.
The geome ic documen a ion o cul u al he i age has
e ol ed signi ican ly o e he yea s, om adi ional su eying
and pho og amme ic echniques o au oma ed wo k lows.
Pho og amme ic echniques ha e seen impo an ad ancemen s,
while deep lea ning is now being in eg a ed in o adi ional
p ocesses, like image ma ching and 3D econs uc ion, hence
imp o ing accu acy and au oma ion in cul u al he i age
documen a ion (Ve ykokou & Ioannidis, 2025). Ea ly e o s
we e he ounda ion o in eg a ing se e al di e en da a
acquisi ion me hods o enhance he accu acy and comple eness
o he geome ic documen a ion p oduc s. The impo ance
o combining mul iple da a acquisi ion echniques o he
geome ic documen a ion o cul u al he i age si es is add essed
by Geo gopoulos (2017), who p o ides a comp ehensi e
o e iew o da a acquisi ion me hods, emphasizing bo h passi e
and ac i e echniques o accu a e geome ic documen a ion.
The need o high-quali y da a collec ion p ocesses, o ensu e
he eliabili y o he esul ing 3D models o cul u al he i age
si es o p ese a ion and analysis is emphasized by Ma oma i
e alii (2019). In hei s udy, Kasapakis e alii (2024) discuss
he applica ion o pho og amme y in cul u al he i age,
highligh ing i s e ec i eness in c ea ing accu a e 3D models o
documen a ion and p ese a ion pu poses. Also, he in eg a ion
o eali y cap u e echnologies, such as 3D scanning and
pho og amme y, wi h la ge-scale 3D p in ing has been explo ed
as an inno a i e app oach o he p ese a ion and ep oduc ion
o his o ical and cul u al he i age (Ga cia-Espinel e alii,
2024). A compa a i e analysis o di e en so wa e packages o
3D modeling o complex geome ies o cul u al he i age si es is
p esen ed by Ve ykokou e alii, (2021), whe e an o e iew o
image-based and scanne -based 3D modeling echniques ha
may be applied o he geome ic documen a ion o cul u al
he i age si es is gi en by Ve ykokou & Ioannidis (2023).
In ecen yea s, nume ous geome ic documen a ion applica ions
ha e been epo ed in li e a u e. Examples include he holis ic
3D digi al documen a ion o he Sain Neophy os Enkleis io is
Monas e y in Paphos, Cyp us, h ough a comp ehensi e app oach
ha in eg a es a ious da a acquisi ion me hods, o cap u e bo h
he angible and in angible aspec s o he monumen (Ioannides
e alii, 2016); a mul i-scale 3D modeling amewo k o damaged
cul u al he i age si es (Ve ykokou e alii, 2016); he c ea ion o
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I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue 1 (2025) www.ijege.uni oma1.i
THE GEOMETRIC DOCUMENTATION OF THE GREEK CULTURAL HERITAGE SITES PARTICIPATING IN THE TRIQUETRA PROJECT
de ailed models o he Sain Ma y s Cons an in B ȃnco eanu and
His Sons wooden chu ch in O adea, Romania, ia pho og amme y
and 3D scanning echniques (He man e alii, 2020); a holis ic 3D
documen a ion app oach applied o he i age monumen s in Rhodes,
G eece combining geode ic, pho og amme ic, and lase scanning
da a acquisi ion me hods (Tapinaki e alii, 2021); he gene a ion
o high- esolu ion 3D models o he mul i-le el documen a ion
o he Me eo a UNESCO si e in G eece h ough pho og amme ic
and su eying echniques (Ioannidis e alii, 2022), in eg a ed in a
web-based amewo k wi h a esponsi e 3D iewe , da a e ie al
mechanisms and VR/AR unc ionali ies (Bou si e alii, 2023); he
geome ic documen a ion o he Mehme Bey Mosque monumen
in Se es, G eece, using a mul i-senso app oach in eg a ing
e es ial lase scanning and pho og amme y (Tsiach a e alii,
2024); he digi al documen a ion o he ambula o y o he Ca hed al
o San iago de Compos ela in Spain, using S uc u e om Mo ion
(S M) pho og amme y (Peña-Villasenín e alii, 2024); he
3D documen a ion o he Clock Towe in Ti ana, Albania using
e es ial lase scanning (Llabani & Abazaj, 2024). These examples
demons a e he a ie y o me hods and echnologies ha can be used
o he digi iza ion and he p ese a ion o cul u al he i age si es.
Mo eo e , Colucci e alii (2024) showed how spa ial
and geome ic da a suppo isk assessmen and ulne abili y
assessmen o cul u al he i age si es, by in eg a ing geome ic
documen a ion in o an INSPIRE-based 3D GIS amewo k
o cul u al he i age. Fu he mo e, Building In o ma ion
Modeling (BIM) has become a use ul ool o cul u al he i age
documen a ion, allowing he in eg a ion o bo h seman ic and
geome ic da a. C isan e alii (2024) p oposed a me hodology
o ans o ming 3D poin cloud da a in o in elligen BIM
models, enhancing he conse a ion, documen a ion and
managemen o cul u al he i age si es. These s udies illus a e
he con inuous e o o use geome ic documen a ion esul s
o he scope o cul u al he i age p ese a ion.
Mo eo e , he geome ic documen a ion o unde wa e
cul u al he i age si es is he ocus o many ecen s udies. C i ical
aspec s o all s ages o image-based unde wa e 3D modeling
p ocesses a e discussed by Ska la os & Ag a io is (2020).
Calan opio & Chiab ando (2024) show he e ec i eness
o unde wa e pho og amme y o c ea e high- esolu ion 3D
models o subme ged a chaeological si es. Addi ionally, he use
o ad anced echnologies, like ul a-high- esolu ion mul ibeam
echo sounde s (UHR MBES), has been shown o imp o e he
mapping o a chaeological emains, as p esen ed in he s udy
by Aba e e alii (2024). Se e al examples o 3D modeling
unde wa e cul u al he i age si es h ough ma ine emo e
sensing and pho og amme ic echniques ha e been epo ed
in li e a u e, such as he ecen applica ions o documen ing
unde wa e cul u al he i age si es in Mal a o he c ea ion o
a i ual museum (Gambin e alii, 2021); 3D econs uc ing
he M/S Helma w eck in No way (Diaman i e alii, 2021) and
he Ch is o o os Shipw eck in G eece (Collina e alii, 2022);
documen ing he unde wa e he i age o he Me honi Bay,
G eece (Le y e alii, 2023); and econs uc ing a clus e o
cannons in he Gul o Pa as, G eece (Lab ianidis e alii, 2024).
Manglis e alii (2021) p opose a oadmap o he sus ainable
alo iza ion o accessible unde wa e cul u al he i age si es,
using augmen ed eali y and i ual eali y echnologies, while
he signi icance o shipw eck a chaeology is highligh ed by
B iggs & Campbell (2023). All hese s udies demons a e he
con inuous ad ancemen s in unde wa e 3D documen a ion
echniques, hus con ibu ing in p ese ing unde wa e cul u al
he i age si es and enhancing hei accessibili y.
PHOTOGRAMMETRIC DOCUMENTATION
This sec ion p esen s he geome ic documen a ion wo k low
ollowed o each si e, de ailing he si e cha ac e is ics, da a
acquisi ion me hods, pho og amme ic p ocessing s eps and inal
esul s. Fi s ly, he documen a ion o Aegina Kolonna is p esen ed,
ollowed by he Sunken Ci y and coas al cul u al he i age o Ancien
Epidau us, and inally, he Sanc ua y o Kalapodi is desc ibed.
Aegina Kolonna
In his sec ion, he geome ic documen a ion o Aegina
Kolonna is p esen ed, including a desc ip ion o he si e, da a
acquisi ion, pho og amme ic p ocessing and he inal esul s.
The si e
Aegina Kolonna is a majo a chaeological si e a he no hwes
ip o he island o Aegina in he Sa onic Gul , G eece. I was one o
he majo hubs o he Aegean B onze Age. The si e lies nex o he
sho e and opens o he sea on he wes side, which is cha ac e ized by
a s eep cli . The p ehis o ic se lemen consis s o an inne a ea and
subu bs on he eas e n side. The si e was abandoned a ound 1200 BC
and la e occupied as a nec opolis du ing he I on Age. I con inued
o lou ish om he A chaic o Roman imes. F om he 6 h cen u y
AD un il a ound AD 1000, he si e was home o a la ge Byzan ine
se lemen . Aegina Kolonna has been he subjec o a chaeological
exca a ions since he 19 h cen u y. Since 1966, he Uni e si y o
Salzbu g has unde aken annual esea ch and es o a ion campaigns
(Pa is London Uni e si y O Salzbu g, 2025).
Since he 1970s, he si e has unde gone se e al es o a ion and
consolida ion e o s. The walls o he inne subu b we e es o ed
and consolida ed mos ly du ing exca a ions in he 1970s and
1980s. Howe e , he ou e subu bs and he wes e n a ea emained
la gely unp o ec ed un il 2015. Due o ex ensi e exca a ions since
he la e 19 h cen u y, many p ehis o ic o a chaic walls in he ou e
subu b ha e been exposed o decades, leading o unde washing o
walls and ounda ions. The deep exca a ion cu s, combined wi h
high-s anding walls, ha e posed signi ican s abili y conce ns.
10 I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue 1 (2025) www.ijege.uni oma1.i
C. IOANNIDIS, K. PAPADIMITRIOU, A. TOURTAS, S. SOILE, F. bOURExIS, P. TOKMAKIDIS, K. TOKMAKIDIS, S. VERYKOKOU & C. POTSIOU
In 2011, a new ex ensi e es o a ion campaign was ini ia ed
unde he di ec ion o K. Spo n and a chi ec A. Tanne (Spo n
e alii, 2017), ocusing on he subu bs wi h scien i ic analysis.
Since 2015, he es o a ion p og am has p io i ized back illing
and consolida ing he walls using a ious scien i ically app o ed
mo a s. A pa icula challenge is he wes e n a ea o Kolonna,
which includes a sac ed si e o e buil by Byzan ine cis e ns and
houses. This a ea was exca a ed in he ea ly 2000s and pa ially
back illed. Howe e , i emains highly ulne able o win e
s o ms and cons an wa e ac ion caused by he hea y ma i ime
a ic be ween Aegina and A hens (wi h comme cial e y boa s
ope a ing e e y hal hou alongside hea y p i a e a ic). Each
yea , he a chaeological zone de e io a es, especially in he wes ,
due o soil up u es and he ongoing isk o collapse.
To add ess hese issues, TRIQUETRA echnologies a e being
employed o measu e geological haza ds ela ed o g ound ins abili ies
and o p o ec he cli s om wa e ac ion and p ecipi a ion. Speci ic
geophysical campaigns a e being conduc ed a he si e.
The wo k plan ollowed wi hin TRIQUETRA includes a
ho ough analysis o he ac o s con ibu ing o he si e’s ongoing
de e io a ion. I is c ucial o di e en ia e be ween na u al wa e
ac ion, wa es p oduced by ship a ic and changes in cu en
beha io . Addi ionally, clima e s udies a e conduc ed o assess
p ecipi a ion pa e ns o e pas decades. Me hodologically, he
p ojec inco po a es pho og amme ic p ocessing and emo e
sensing image y analysis, as well as chemical and physical s udies
o he endange ed cli s. This app oach acili a es he iden i ica ion
and quan i ica ion o isks and he implemen a ion o isk
mi iga ion s a egies. P o en me hods, along wi h hose de eloped
wi hin TRIQUETRA, a e applied o minimize isks and de elop
long- e m s a egies o p o ec ing he cli s om u he damage.
Da a acquisi ion
The Labo a o y o Pho og amme y o he Na ional Technical
Uni e si y o A hens (NTUA), led he pho og amme ic
documen a ion o he Aegina Kolonna si e, p oducing a
de ailed 3D model, poin cloud, DSM and o homosaics. The
pho og amme ic su ey was conduc ed on June 25, 2024 (Fig.
1). This documen a ion was implemen ed wi hin he con ex o
he TRIQUETRA p ojec , wi h he aim o suppo long- e m
moni o ing o he si e and in o m p ese a ion s a egies.
Fo he ae ial da a collec ion, a DJI Ma ic 3 En e p ise
d one was used o cap u e 945 e ical ae ial images, co e ing
he en i e si e, p o iding an o e iew o he si e’s opog aphy
(Fig. 2a), o ensu e high- esolu ion documen a ion o complex
s uc u es such as slopes, walls, and in ica e ea u es, 4,900
oblique ae ial images we e cap u ed a lowe al i udes (Fig. 2b).
Rep esen a i e oblique images a e shown in Fig. 3. Addi ionally,
a DJI Ma ic 2 P o d one was deployed o cap u e 930 images
o a eas su ounding he Kolonna, as well as a eas wi hin he
a chaeological si e and he museum acades (Fig. 4).
Conce ning he g ound su ey, 15 p e-ma ked G ound Con ol
Poin s (GCPs) we e placed a ound he si e and measu ed in he
G eek Geode ic Re e ence Sys em (GGRS ‘87) using a Leica
Fig. 1 - Images om he pho og amme ic campaign in Aegina Kol-
onna, led by he Lab. o Pho og amme y, NTUA wi hin he
TRIQUETRA p ojec
Fig. 2 - Dis ibu ion o he UAV e ical ae ial images (a) and he whole se
o UAV e ical and oblique images (b) o e he 3D model o he
en i e a ea su ounding he a chaeological si e o Aegina Kolonna
Fig. 3 - Rep esen a i e oblique images showcasing he slopes, walls
and o he si e de ails o Aegina Kolonna
11
I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue 1 (2025) www.ijege.uni oma1.i
THE GEOMETRIC DOCUMENTATION OF THE GREEK CULTURAL HERITAGE SITES PARTICIPATING IN THE TRIQUETRA PROJECT
1200 GNSS ecei e . The NTRIP RTK me hod was employed
o ecei e co ec ions om he Me icaNe GNSS pe manen
s a ions ne wo k. Addi ionally, 10 cha ac e is ic poin s wi hin he
si e we e measu ed o u he imp o e geo e e encing accu acy.
The dis ibu ion o he GCPs is illus a ed in Fig. 5.
Pho og amme ic p ocessing
The pho og amme ic p ocessing was implemen ed using
he Agiso Me ashape P o essional so wa e, ollowing a mul i-
iew 3D econs uc ion wo k low.
The i s s ep included he es ima ion o he in e io and
ex e io o ien a ion o all 6,694 images and he compu a ion o he
coo dina es o a spa se poin cloud con aining ~2.4 million poin s,
consis ing o he au oma ically ex ac ed ie poin s. This p ocess
includes he s eps o au oma ic iden i ica ion o o e lapping images,
image ma ching and ea u e acking as well as he main p ocess
o S uc u e om Mo ion (S M). Geo e e encing was conduc ed
using 15 GCPs, while addi ional check poin s we e used o alida e
posi ional accu acy. The geo e e encing achie ed a oo mean
squa e (RMS) e o o ~4 cm o GCPs and 6 cm o check poin s.
The s age o dense poin cloud gene a ion ollowed. This
s age in ol es (i) pe o ming dense image ma ching o selec ed
pai s o o e lapping images wi h known in e io and ex e io
o ien a ion pa ame e s, hus p oducing a se o dep h maps o
he e e ence images, and (ii) con e ing hem in o 3D poin s, by
p ojec ing hem in o space o econs uc he dense poin cloud.
3D su ace econs uc ion was he nex s ep. This p ocess in ol es
gene a ing a polygonal mesh model using he dense poin cloud.
Tex u e mapping was he inal s age, o p oducing a high-
esolu ion ex u e o he 3D mesh, using he o ien ed images.
In addi ion o p oducing 3D geome ic documen a ion p oduc s,
he pho og amme ic wo k low led o he p oduc ion o high-
esolu ion o homosaics along wi h a digi al su ace model o he si e.
Resul s
The 3D documen a ion o Aegina Kolonna esul ed in he
p oduc ion o high-accu acy pho og amme ic da ase s, which
suppo a chaeological analysis, conse a ion planning as well as
isk assessmen wi hin he TRIQUETRA p ojec .
The p oduced dense poin cloud consis s o ~61 million
poin s (Fig. 6). I p ese es ine de ails o he a chaeological
Fig. 4 - Dis ibu ion o images cap u ed by he DJI Ma ic 2 P o d one a ound Aegina Kolonna along wi h he spa se poin cloud
Fig. 5 - Dis ibu ion o he GCPs measu ed in he a chaeological si e o
Aegina Kolonna supe imposed on he o homosaic o he si e
Fig. 6 - Dense poin cloud o he a chaeological si e o Aegina Kolonna

12 I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue 1 (2025) www.ijege.uni oma1.i
C. IOANNIDIS, K. PAPADIMITRIOU, A. TOURTAS, S. SOILE, F. bOURExIS, P. TOKMAKIDIS, K. TOKMAKIDIS, S. VERYKOKOU & C. POTSIOU
si e and se es as a c i ical da ase o a chaeological s udies
and conse a ion e o s, enabling p ecise measu emen s and
he de ec ion o changes o e ime.
The gene a ed high- esolu ion 3D ex u ed model accu a ely
depic s he geomo phology and a chi ec u al de ails o Aegina
Kolonna. The 3D mesh model consis s o ~9.9 million e ices
and 19.8 million aces. The ex u ed ende ed o he model led o
a de ailed isual ep esen a ion o s uc u al elemen s o he s udy
Fig. 7 - Views o he 3D model o he a chaeological si e o Aegina Kolonna wi hou ex u e (le ) and wi h ex u e ( igh )
Fig. 8 - Views o pa o he 3D model o he a chaeological si e o Aegina Kolonna wi hou ex u e (le ) and wi h ex u e ( igh ).
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THE GEOMETRIC DOCUMENTATION OF THE GREEK CULTURAL HERITAGE SITES PARTICIPATING IN THE TRIQUETRA PROJECT
a ea. The 3D model cap u es no only he main a chaeological si e,
bu also he su ounding e ain, p o iding a aluable esou ce
o u u e moni o ing o s uc u al in eg i y and en i onmen al
changes. Views o he non- ex u ed and ex u ed 3D model a e
illus a ed in Fig. 7 (en i e model) and Fig. 8 (zoom-in iews).
Fu he mo e, a DSM was gene a ed, allowing o de ailed
e ain analysis. The DSM, p oduced a 1 cm esolu ion,
accu a ely cap u es he ele a ion a ia ions ac oss he si e.
The ele a ion alues ange om -4 m o 26 m, e lec ing bo h
he na u al opog aphy and he s uc u al emains o Aegina
Kolonna. The DSM enables hyd ological and opog aphical
assessmen s, con ibu ing o he e alua ion o e osion isks and
wa e uno pa e ns. Fig. 9 shows he p oduced DSM.
Finally, high- esolu ion o homosaics we e p oduced o
de ailed planime ic analysis o he si e. Speci ically, o hmosaics
wi h a g ound sampling dis ance (GSD) o 1 cm and 2.5 cm
we e gene a ed. The o homosaics e e o he GGRS87 / G eek
G id (EPSG::2100) coo dina e sys em and se e as a aluable
ool o GIS-based analyses. The gene a ed o homosaic wi h a
GSD o 1cm is illus a ed in Fig. 10.
The pho og amme ic documen a ion o Aegina Kolonna
p o ides a da ase o high geome ic accu acy, allowing o s uc u al
assessmen s, a chaeological analysis and conse a ion planning.
The 3D ex u ed model o he si e enables de ailed isualiza ion
and moni o ing o he si e’s a chi ec u al ea u es, while he
p oduced dense poin cloud and DSM con ibu e o en i onmen al
assessmen s and long- e m p ese a ion s a egies. Mo eo e , he
gene a ed 2D p oduc s (o homosaics) along wi h he 3D ou pu s
suppo a chaeological mapping and aid in si e managemen .
Beyond hei immedia e applica ions, he gene a ed da ase s
can se e as he basis o u u e moni o ing o he si e, h ough
applica ion o change de ec ion me hods ha may suppo
conse a ion e o s. Wha is mo e, he in eg a ion o he gene a ed
p oduc s in o he TRIQUETRA Knowledge Base Pla o m can
enhance isk assessmen by p o iding accu a e spa ial da a
o e alua ing he s uc u al s abili y o he si e and assessing
en i onmen al h ea s. The 3D pho og amme ic p oduc s also
o m he ounda ion o he Digi al Twin o Aegina Kolonna,
enabling u he applica ions such as he Augmen ed Reali y
(AR) app o he TRIQUETRA p ojec o ci izen engagemen .
The sunken ci y o Ancien Epidau us and i s coas al he i age
In his sec ion, he geome ic documen a ion o he Sunken
Ci y o Ancien Epidau us and i s coas al cul u al he i age is
p esen ed, including a desc ip ion o he si e, da a acquisi ion,
pho og amme ic p ocessing and he inal esul s.
The si e
Ancien Epidau us comp ises a cul u al he i age si e o
highly signi ican unde wa e and coas al emains da ing back
o he 12 h cen u y B.C. The Sunken Ci y is loca ed in he bay
o Agios Vlasios, nea Ancien Epidau us. Bio-e osion is one o
he mos signi ican isks a ec ing hese unde wa e and coas al
a chaeological indings. The Sunken Ci y and he su ounding
coas al he i age a e slowly de e io a ing due o wa e exposu e
and mic oo ganisms. Addi ionally, sea le el ise poses a se e e
h ea o coas al a chaeological emains, while coas al e osion
is ano he majo isk. Flooding on he coas al land, sedimen
deposi ion, and embankmen cons uc ion o po de elopmen
u he endange he si e. Damage is also caused by illegal
moo ing o ou is boa s, while exposu e o chemicals, seismic
ac i i y and po en ial andalism ep esen addi ional h ea s.
Sys ema ic conse a ion and p omo ion e o s ha e al eady
begun, alongside ongoing exca a ions ac oss he si e.
The 3D modeling o CH si es, pa icula ly unde wa e
an iqui ies, p esen s signi ican challenges due o he complexi y
Fig. 9 - DSM o he a chaeological si e o Aegina Kolonna
Fig. 10 - O homosaic o he a chaeological si e o Aegina Kolonna
14 I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue 1 (2025) www.ijege.uni oma1.i
C. IOANNIDIS, K. PAPADIMITRIOU, A. TOURTAS, S. SOILE, F. bOURExIS, P. TOKMAKIDIS, K. TOKMAKIDIS, S. VERYKOKOU & C. POTSIOU
and speci ic condi ions o he aqua ic en i onmen . The de ailed
3D su ey o unde wa e and coas al CH esou ces in Ancien
Epidau us, combined wi h li e a u e e iews and a chaeological
s udies, will se e as he knowledge base o he TRIQUETRA DSS.
These e o s aim o: (i) p e en u he de e io a ion o he si e due o
o e ou ism, na u al haza ds and human-induced h ea s, (ii) ensu e
s uc u ed p o ec ion o he CH si e and (iii) de elop sus ainable
ou ism s a egies and p opose es o a ion solu ions o he si e.
Cu ing-edge da a collec ion echniques in su eying,
pho og amme y and emo e sensing ha e been implemen ed.
The au ho s wo ked closely wi h he local municipali y, he
A chaeological Se ice o he a ea, he Ma ine An iqui ies
Se ice, local guides and a el agen s. High-accu acy
pho o ealis ic 3D models o he coas al and unde wa e
an iqui ies we e gene a ed. Fo he coas al pa o Ancien
Epidau us, a combina ion o ae ial and close- ange
pho og amme y, e es ial lase scanning, and ae ial LiDAR
was used. Fo he unde wa e pa , hyd og aphic mul i-beam
sona su eys and unde wa e pho og amme y we e employed.
A common e e ence ne wo k was es ablished o all eali y
cap u e su eys, ensu ing accu acy a e e y s ep. A key ocus o
his wo k is he de ec ion and moni o ing o changes, damage,
o de e io a ion, wi h a sys ema ic app oach o iden i ying
changes a an ea ly s age o allow o imely in e en ions. All
collec ed su ey da a we e uploaded o he TRIQUETRA online
pla o m o u he p ocessing, analysis and collabo a ion.
The high-accu acy 3D su ey o Epidau us an iqui ies and
hei su ounding a ea will se e as a e e ence amewo k o
scien i ic esea ch and o in eg a ing he ou comes o he p ojec .
Da a acquisi ion
The Labo a o y o Topog aphy (LabTop) o he School o
Ru al and Su eying Enginee ing o he A is o le Uni e si y
o Thessaloniki (AUTh) unde ook he pho og amme ic
documen a ion o he unde wa e and coas al CH esou ces
in Ancien Epidau us, aiming o cap u e he geome y o he
cul u al he i age asse s o he Sunken ci y and he su ounding
coas o assessing a eas ulne able o en i onmen al and
s uc u al isks. The da a collec ion mission in Epidau us was
conduc ed om May 13 h o May 16 h, 2024 and i s goal was o
collec da a o ou di e en ypes (Fig. 11), i.e., ae ial LiDAR
da a, ae ial images, unde wa e images and mul ibeam SONAR
da a. Implemen ing and measu ing GCPs was also a p e-
equisi e o some o he abo e-men ioned su eys.
A DJI Ma ice 300 RTK UAV was used o he ae ial
LiDAR su ey, in combina ion wi h DJI’s L1 LiDAR senso .
Ma ice 300 RTK in eg a es dual GNSS senso s and an ennas
and can ly wi h su ey g ade accu acy, bu also geo ags he
images wi h su ey g ade accu acy. Fo his o happen, he
con olle mus be connec ed o ei he a ne wo k o GNSS
e e ence s a ions ia NTRIP o o a base GNSS ecei e
cas ing NTRIP. The second scena io was used o all cases in
Ancien Epidau us. L1 acco ding o he manu ac u e has an
accu acy o 5cm, a 20Mpixels came a o colo ing he poin
clouds cap u ed, in eg a ed gimbal and IMU and eco ds iple
e u n o each pulse, so i can pene a e e en hea y ege a ion
and cap u e g ound poin s unde nea h. The coas al a ea o
Ancien Epidau us was su eyed in i e au onomous ligh s.
Th ee o hese ligh s u ilized he e ain- ollow unc ion due o
signi ican heigh a ia ions in he e ain, while he emaining
wo ligh s did no use his unc ion, conside ing he heigh
di e ences in hose a eas o be insigni ican . The Digi al
Ele a ion Model (DEM) iles needed o he e ain- ollow
unc ion we e c ea ed om da a p o ided by he na ional
Fig. 11 - Images om he campaign in Epidau us, led by he Lab. o
Topog aphy, AUTh wi hin he TRIQUETRA p ojec
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THE GEOMETRIC DOCUMENTATION OF THE GREEK CULTURAL HERITAGE SITES PARTICIPATING IN THE TRIQUETRA PROJECT
cap u ed om he wo came as and an addi ional 308 images o
de ails we e cap u ed wi h a medium o ma Hasselblad X1D II in
a wa e p oo housing (Fig. 13). The senso s on he GoP o came as
a e 1/1.9” and a esolu ion o 27Mpixels, while X1D II has 50
million e ec i e pixels and was combined wi h a 21mm lens,
cadas e and uploaded o he ligh con olle . Th oughou he
i e ligh s, a o al o 340 million poin s we e collec ed, wi h a
spa ial esolu ion o app oxima ely 170 poin s pe squa e me e .
The esul ing LiDAR poin cloud is illus a ed in Fig. 12.
The same UAV was used o cap u ing ae ial images (Fig. 13),
o he pho og amme ic su ey o he a ea. Again, i e ligh s
we e conduc ed, h ee wi h he e ain- ollow unc ion and wo
wi hou . In o al, 4,949 e ical images we e cap u ed du ing he
i e au onomous ligh s. To cap u e he exca a ion a ea in g ea e
de ail, wo addi ional ligh s we e ca ied ou : one in ol ed
manually cap u ing e ical images a a lowe al i ude, and he
o he in ol ed manually cap u ing oblique images o he exca a ed
ancien uins. Toge he , hese wo ligh s con ibu ed an addi ional
668 images o he da ase . All he necessa y ligh pe mi s om he
Hellenic Ci il A ia ion Au ho i y, we e g an ed well in ad ance.
Fo he unde wa e pho og amme ic su ey o he “Mansion”
a he sou h bay o Epidau us, a a ie y o came as and scuba
di ing equipmen ha e been used. The eason o ha is ha
due o he e y shallow dep hs in mos pa s o he mansion, a
big, hea y came a sys em wi h ligh s would be e y di icul o
ope a e. Addi ionally, he mansion’s uins we e o e popula ed by
he enomous u chin species “Diadema Se osum”, equi ing he
di e s o a oid con ac wi h he uins unde any ci cums ances.
Finally, a me hod p e iously employed by LabTop was adap ed
o hese condi ions: wo GoP o He o 11 Black came as we e
moun ed on a 1.20m od, igidly ixed a bo h ends. In addi ion,
wo unde wa e ligh s each p oducing 21,000 lumens, we e
a ached o he od, which was hen secu ed unde a di e ’s buoy.
Wi h his con igu a ion, he came as we e cap u ing sligh ly
unsynch onized ( hus he “pai s” o images canno be used as a
igid came a sys em) images (Fig. 13) in imelapse mode e e y 2
seconds and he di e s ayed sa ely on he su ace na iga ing he
buoy in he same pa e n ha d one su eys a e conduc ed in d y
land. The wo came as wi h hei ul a-wide lenses we e able o
cap u e images wi h enough o e lap o pho og amme y e en in
dep hs o less han 0.5m, which was he case in se e al pa s a
he Epidau us subme ged mansion. In o al 13,529 images we e
Fig. 12- LiDARpoin cloudde i ed om5LiDAR ligh sinEpidau us
Fig. 13 - Images cap u ed wi h he UAV (up), GoP o came a (middle)
and Hasselblad X1D II (down) in Epidau us
22 I alian Jou nal o Enginee ing Geology and En i onmen , Special Issue1 (2025) www.ijege.uni oma1.i
C. IOANNIDIS, K. PAPADIMITRIOU, A. TOURTAS, S. SOILE, F. bOURExIS, P. TOKMAKIDIS, K. TOKMAKIDIS, S. VERYKOKOU & C. POTSIOU
he i age—TRIQUETRA”, which is a P ojec unded by he EU
HE esea ch and inno a ion p og am unde GA No. 101094818.”
CONCLUSIONS
The aim o his s udy was o apply s a e o he a
pho og amme ic echniques o he geome ic documen a ion
o he h ee G eek pilo si es o he TRIQUETRA p ojec ,
namely, Aegina Kolonna, he Sunken Ci y in Epidau us and i s
coas al cul u al a ea as well as he Kalapodi si e, con ibu ing
o hei p ese a ion. The main s ages o he pho og amme ic
campaigns consis o da a acquisi ion and pho og amme ic
p ocessing. The esul s o he geome ic documen a ion o
he h ee cul u al he i age si es a e u he used and analyzed
wi hin he TRIQUETRA p ojec o assessing hei s uc u al
condi ions and moni o ing he impac o ex e nal ac o s, like
clima e change, on hese monumen s. The p oduced geome ic
documen a ion esul s a e o high impo ance, so hey will be
sha ed wi h he scien i ic communi y and he public, aising
awa eness o he challenges ha ou cul u al he i age aces
unde he h ea o clima e change and na u al haza ds.
ACKNOWLEDGMENTS
This wo k is based on p ocedu es and asks implemen ed
wi hin he p ojec “Toolbox o assessing and mi iga ing
Clima e Change isks and na u al haza ds h ea ening cul u al
Fig. 27 - De ailed iew o he deli e ed o homosaic o Kalapodi
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Recei ed Feb ua y 2025 - Accep ed July 2025
C. IOANNIDIS, K. PAPADIMITRIOU, A. TOURTAS, S. SOILE, F. bOURExIS, P. TOKMAKIDIS, K. TOKMAKIDIS, S. VERYKOKOU & C. POTSIOU