Developing a Workflow for the Use of Unmanned Aerial Vehicles for Cadastral Mapping in Ghana

This paper proposes a generic workflow for using Unmanned Aerial Vehicles (UAV) to produce acceptable cadastral plans in Ghana. This was done by firstly verifying in the field UAV restricted zones specified by the Ghana Civil Aviation Authority (GCAA) and subsequently analyzing ground and aerial survey data from two sites within the Tema Municipality. The data analyzed consisted of one set of boundary coordinate data of the sites obtained from a static Global Navigation Satellite System (GNSS) survey and another set from on-screen digitization of site boundaries from aerials obtained from a Mavic Air UAV weighing 430 g with a camera resolution of 12 megapixels flying at altitudes of 40 and 60 m. A comparison of the two sets of boundary coordinates data showed differences under the limit of +/-3 ft specified by the Survey and Mapping Division (SMD) of the Lands Commission of Ghana. The paper thus outlines a generic workflow as follows: (1) Determining if selected site is within a flight restricted zone (2) Undertaking field reconnaissance to determine appropriate flight parameters and ground control point locations (3) Processing UAV imagery to obtain orthomosaics (4) Performing on-screen digitizing of site boundaries from orthomosaics and (5) Obtaining accurate boundary turning point coordinates from digitized boundary. The paper concludes that this approach if accepted may be used in obtaining multiple cadastral plans within built up areas from a single UAV flight and recommends that UAV and ground control data be submitted in Geotiff and Rinex formats respectively to facilitate checks by the Examinations Unit of the SMD.