Integration of UAV Photogrammetry and Ground Control Points for Large-Scale Topographic Mapping in Ibadan

Unmanned Aerial Vehicle photogrammetry has emerged as a cost-effective alternative to conventional topographic surveying for producing high-resolution spatial data. This study investigates the integration of UAV photogrammetry and strategically placed ground control points for large-scale topographic mapping of a five-square-kilometre study area within the Bodija district of Ibadan, Oyo State. A fixed-wing UAV equipped with a twenty-megapixel RGB camera is deployed at a flying height of one hundred metres, achieving a ground sampling distance of approximately 2.5 centimetres. Ground control points are established using differential GNSS, and Structure from Motion photogrammetric processing is performed in Agisoft Metashape to generate a high-resolution orthomosaic and digital surface model. Accuracy assessment is conducted against independently surveyed check points, and results indicate root mean square errors of below five centimetres in the horizontal plane and below eight centimetres vertically. The generated topographic products are compared with 1:2500 scale maps produced by the Oyo State Geographic Information Agency to assess equivalence for urban planning applications. The study demonstrates that UAV photogrammetry, when coupled with a well-distributed GCP network, satisfies the accuracy requirements for cadastral-grade mapping in urban environments. Recommendations address optimal GCP density, flight planning parameters, and data processing workflows for practitioners operating in South West Nigeria. Keywords: UAV photogrammetry, topographic mapping, ground control points, Ibadan, Structure from Motion.