Conducting a photogrammetric survey campaign (creation of topographic maps from aerial and spatial imagery) at a historic site such as the Basilica of Santa Caterina D’Alessandria in Galatina involves detailed planning and the use of advanced techniques to ensure maximum precision and data quality. This article outlines the main technical processes, steps, and activities involved in such a campaign, which CETMA expertly conducted.

Preliminary Planning and Information Gathering

The initial phase of the photogrammetric survey involves gathering all available information about the basilica. This includes:

  • Maps and Drawings: Collecting architectural plans and topographical maps.
  • Photographs: Gathering existing photographs, including aerial and ground-level images.
  • Historical Data: Compiling historical records and documentation to understand the site’s evolution and significance.

The specific objectives of the survey are defined during this phase, whether it’s creating a detailed 3D model, analyzing structural conditions, or documenting the basilica for conservation purposes.

Obtaining Permissions and Conducting Risk Assessments

Given that the Basilica of Santa Caterina D’Alessandria is likely under conservation protection, securing the necessary permissions for drone usage is crucial. This involves:

  • Liaising with Conservation Authorities: Ensuring compliance with legal and regulatory frameworks.
  • Risk Assessment: Conducting a comprehensive risk assessment to ensure the safety of both the flight operations and the data acquisition process. This includes assessing potential hazards and implementing measures to mitigate them.

Flight Planning

Using specialized flight planning software, optimal flight paths and altitudes are defined to ensure complete coverage of the basilica and sufficient image overlap. Key considerations include:

  • Coverage: Ensuring that the entire site is covered by the drone’s flight path.
  • Image Overlap: Planning for adequate front and side overlap (typically 70-80%) to ensure high-quality photogrammetric results.

Ground Control Points (GCPs)

To enhance the accuracy of the 3D model, ground control points (GCPs) with known coordinates are placed strategically around the site. These GCPs serve as reference points during the image processing phase.

Drone and Camera Operations

The actual data acquisition involves executing flights according to the pre-defined plan. During the flights:

  • Image Capture: Drones capture high-resolution images with the planned overlap.
  • Digital Cameras: In addition to drone imagery, digital cameras are used to capture detailed images of areas that may not be adequately covered by the drone, such as interiors, architectural details, and vertical surfaces.

Data Processing and Analysis

After the data acquisition, the images are processed using photogrammetric software to create detailed 3D models and other deliverables. This phase includes:

  • Aligning Images: Using the captured images and GCPs to align and stitch the photos together accurately.
  • Model Creation: Generating a precise 3D model of the basilica.
  • Analysis: Analyzing the model for structural conditions or documenting it for conservation purposes.


The photogrammetric survey campaign at the Basilica of Santa Caterina D’Alessandria in Galatina, conducted by CETMa, demonstrates the meticulous planning and advanced techniques required to achieve high-quality results. By gathering comprehensive information, securing necessary permissions, conducting thorough risk assessments, and using advanced drone and camera technologies, CETMa successfully created detailed and accurate 3D models that serve various purposes, from structural analysis to conservation documentation.