Xlendi, Malta

Mission director: Timmy Gambin, University of Malta


Presentation

Survey co-directed by:
Archaeology: Timmy Gambin University of Malta, Jean-Christophe Sourisseau, CCJ, CNRS
Photogrammetry: Pierre Drap, LIS, CNRS and Kari Hyttinen

This work, started on July 2014 and carried out with the support of the Superintendence of Cultural Heritage of Malta, was partially funded by the National Research Agency (until 2017) within the framework of the GROPLAN project whose objective is the identification and location of objects in the studied archaeological sites.

Over the past years, local heritage authorities in Malta have conducted a number of systematic remote sensing surveys off the coasts of the Maltese Islands. One such collaborative project resulted in the discovery of a well-preserved ancient shipwreck. From initial studies conducted on the site it was established that the site is datable to approximately 7th century BC at a depth of 110 m. This shipwreck may offer new and significant information about Phoenician seafaring and trade in the central Mediterranean during the archaic period. To date, little is known about the earliest contact of Phoenician mariners with the Maltese islands. Most archaeological evidence stems mainly from funerary evidence. This discovery may be considered as one of the best-preserved archaeological sites in Malta datable to the early Phoenician period, because it was established that the bulk of the cargo still remains buried in the sediments.

The archaeological site survey is carried out by photogrammetry. This technique is effective when it is a difficult area of access where human intervention is difficult or even impossible, and requires a low cost implementation and in a short time. We work on documents composed of theoretical 3D models, photographs and 3D dense point clouds. The use of a remote operated vehicle, side scan sonar and a sub bottom profiler enabled the discovery, study and assessment of this deepwater shipwreck.

Time line analysis

xlendi 3D model                    xlendi 2D model

Time line analysis, a way to study and monitoring change over the time: on the left in 3D using photogrammetry survey from 2009 to current state, on the right time line in 2D using orthophoto site blending between years ...

Note: a WebGL-enabled browser is needed to run the models presented here. Please refer to this page for a quick HOWTO or click here to test your browser.

Archaeological analysis

The main idea of this research work is the link between measurement and knowledge.
The underwater archeology survey is based on the study of a certainly well-established corpus of knowledge, but possibly still in question. The survey approach proposed here therefore implies a formalization of the studied corpus, which will drive the survey process. The knowledge formalization is based on ontologies. The ontology developed within the framework of this project takes into account the manufactured items surveyed and the photogrammetry process which is used to measure them. Each modeled item is therefore represented from the measurement point of view and has access to all the photogrammetric data that contributed in the measurement process. To this extent we developed two ontologies: one dedicated to photogrammetric measurement and the geo-localization of the measured items, whereas the other is dedicated to the measured items, principally the archaeological artefacts, describing their dimensional properties, ratios between main dimensions, and default values. Within this project, these two ontologies were aligned in order to provide one common ontology that covers the two topics at the same time. The development architecture of these ontologies was performed with a close link to the Java class data structure, which manages the photogrammetric process as well as the measured items.
The architecture of the developed framework is based on a close link between, on the one hand, the software engineering aspects and the operative modeling of the photogrammetry process, artefacts measured by photogrammetry in the context of this project and, on the other hand, with the ontological conceptualization of the same photogrammetry process and surveyed artefacts. The present implementation is based on a double formalism, JAVA, used for computation, photogrammetric algorithms, 3D visualization of photogrammetric models, and cultural heritage objects, and then for the definition of ontologies describing the concepts involved in this photogrammetric process, as well as on the surveyed artefacts.
xlendi 3D model with ontology queries                xlendi 2D model with ontology queries

Ontology queries: From 3D model (on the left) and on 2D model (on the right).

Amongst the advantages of the photogrammetric process is the possibility of providing several 2D representations of the measured artefacts. Our ontology makes use of this advantage to represent the concepts used in photogrammetry, and to be able to use an ontology reasoner on the ABox representing photogrammetric data. In other words, this photogrammetric survey is expressed as an ontology describing the photogrammetric process, as well as the measured objects, and that was populated both by the measurements of each artifact and by a set of corresponding data.
This architecture is based on the procedural attachment where the ontology is considered as a homologous side of the JAVA class structure that manages the photogrammetric survey and the measurement of artefacts. This allows the benefiting from a reasoning over the ontologies, as well as the intensive calculations using the JAVA programming language with the same interface.
This approach ensures that all the measured artefacts are linked with all the observations used to measure and identify them.

Movies and presentations


Here a video of the first campain and the first results of photogrammetric restitution: ortophoto and 3D model.


Here a video of the 2016 campain



Ortophoto and 3D mesh model

Here you see the ortophoto made by photogrammetric restitution. Approximately 5000 high resolution photographs have been oriented and 330 milion 3D points computed. A mesh with 200 milion triangles have been generated and an high definition orthophoto have been computed. Link here or through the image below.

Xlendi orthophoto



Below the 3D mesh model loaded with Sketchfab. Navigate or start animation and take screenshot, scroll down to select amphora name and see its location.