A photogrammetric approach for map updating using UAV in Rwanda

Geospatial data is an important asset for development planning in every country. Rwanda is experiencing a steady period of growth in terms of both population and economic development, which emphasizes the need for regularly updated maps so that development can be planned in effective way. The existing basemap produced from the 2008 orthophoto campaign - which has been used to guide all country development planning - is outdated. This can result in unreliable decisions, hence an update is necessary. Conventional methods for spatial data acquisition are aerial photogrammetry and terrestrial surveying. They are, however, time consuming and costly. A new approach is needed for rapid spatial data collection at a low cost. This study will present how this can be achieved using Unmanned Aerial Vehicles (UAVs); a new remote sensing tool capable of acquiring airborne images which has the potential to provide information with a very high spatial and temporal resolution at a low cost. The main objective of this study was to use UAV imagery to produce a high quality orthophoto to update geospatial data. In order to achieve this, a DJI Phantom 2 Vision Plus quadcopter was used to collect 954 images at a flying height of 50 m. Using adequate photogrammetric software, an orthophoto of 3.3 cm GSD covering 0.095 km² was produced. With appropriate ground control points, an absolute positional accuracy of 7.9 cm RMSE was achieved. Features of interest were digitized using ArcMap at 1/1000 scale and updated in the existing basemap. This study has demonstrate that UAV is a useful platform for obtaining high-resolution aerial images for basemap updating at a sustainable cost.