100 ha LiDAR survey of the Royal Palaces of Abomey

The context

The Royal Palaces of Abomey are one of the most emblematic UNESCO World Heritage sites in West Africa. 100 hectares of perimeter walls, royal courtyards, traditional earthen buildings and heterogeneous tree canopy, much of which covers ancient archaeological structures. The ANPT (Agence Nationale de Promotion des Patrimoines et de développement du Tourisme) wanted a centimetre-accurate georeferenced base usable for conservation, restoration and international funding applications. Classical photogrammetry would have left everything hidden by vegetation invisible. Only airborne LiDAR could reconstruct the bare ground under canopy, with no human intervention on the historic structures.

Our method

Four days of field work in high-density airborne LiDAR, with a rigorous GCP-RTK protocol to anchor the cloud in the UTM 31N coordinate system. Double-grid flights at 50 % minimum overlap to guarantee uniform tree-canopy coverage. Prior coordination with ANAC Bénin, the ANPT and the site management to authorise flights over the listed structures. Processing took two weeks of GIS engineering: GNSS post-processing, pass merging, automatic cloud classification (ground, low vegetation, high vegetation, built, collapsed walls), centimetric DTM generation, canopy height model and fine geometric extractions.

What we delivered

• Classified, georeferenced LAS/LAZ point cloud (~10 pts/m² useful)
• High-resolution colour orthophoto (2-3 cm/pixel)
• DTM, DSM and CHM in GeoTIFF format
• Extraction of road and historic-path footprints (SHP)
• Extraction of traditional building footprints
• Extraction of perimeter walls and their remains
• Textured 3D model of the most emblematic structures (OBJ + GLB)
• Technical report with methodology, quality controls and achieved accuracy

The outcome

ANPT now has a centimetric reference dataset to steer site conservation over the long term. Historic paths hidden for decades by vegetation are visible again in the models; collapsed walls are mapped to the cm; produced documentation meets international heritage documentation standards (CIDOC CRM, IIIF). To our knowledge, this is the largest heritage LiDAR survey ever completed in Benin and one of the most emblematic in West Africa. The data also becomes a communicating base for international funding applications and tourism promotion of the site.