Aerial mapping and 3D modelling of ‘Tombs of the Kings’ archaeological site in Paphos

The project focuses in 8 archaeological sites in Nea Paphos: the ‘Acropolis, Agora and Saranda Colones’, the ‘Residential area’, the ‘Habrour and city wall area’, the ‘Fabrika and theater’, the ‘Chysopolitissa and East Ag Pavlos Area’, the ‘North West City Gate’, the ‘Toumballos Area’ and last but not least, the ‘Necropolis – Tombs of the Kings’.

For the execution of the project, Geoimaging ltd was asked to participate and support this project with our high-technology mapping solutions. More specifically, our responsibility was to provide an aerial mapping survey as well as a 3D model of the ‘Necropolis-Tombs of the Kings’ area. It’s worth mentioning that the famous ‘Tombs of the Kings’ is one of the most important archaeological sites of Cyprus that has been included in the UNESCO World Heritage Sites list since 1980.

According to the project’s requirements, the overall site had to be recorded and mapped with ortho-photos in a scale of 1:50, whereas the exposed mosaics had to be documented in higher graphic scales with HR ortho photos to achieve a higher detail. Our company’s role was to produce a high-resolution ortho-corrected photomosaic of the site (5cms or less). To achieve this result, the general process included i. aerial photogrammetry survey using a drone with adequate overlap and resolution,
ii. identification and setting up of a Ground Control Points (GCP) (x,y,z) network covering all site features (x,y,z) used to georeference the aerial imagery, measured with differential GPS and Total Station,
iii. production of the overall ortho-corrected photomosaic of the site,
iv. a georeferenced 3D model

The GCP network establishment lasted 3 days and more than 660 control points were measured in total. During this process, triangulation pillar stations and trigonometric marker points identified in the wider area and then printed targets/markers were placed on the ground in locations specified by our surveyors. These had to be large enough to be visible in aerial photos. Then, by utilizing the information of the existing trigonometric network we surveyed these targets and provided their horizontal and vertical coordinates by using a survey-grade GPS receiver.

Once the GPC network was set up, the next step was to schedule the flight over the site-area to capture the imagery. Our experienced personnel flied the drone over the site area, taking a series of photos with a large format aerial camera. During this process, multiple overlapping photos of the ground are captured from different angles as the aircraft flies autonomously along a flight path that we specify beforehand. This ensures we would not miss anything and enough image overlap is achieved. For the specific survey, the flight was executed at a height of 40m, and more than 2500 images were captured.

After acquiring the aerial images, the data were then processed properly in the office to rectify and georeferenced the imagery. During this process, images were aligned together based on the known ground target locations. By using check points the accuracy of the final product was assessed, which was less than 5cm (the permissible error limit). The final deliverables was a 3D model as well as a high-resolution orthographic photomosaic of the archaeological site of ‘Necropolis – Tombs of the Kings’.

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