Google earth as image source in photogrammetric mapping of KNUST campus
The increasing demand for maps resulting from the unending and ever-increasing activities of man has made the provision of maps a subject of considerable importance. This paper describes a practical application of Google Earth satellite images for the production of a planimetric map of the Kwame Nkrumah University of Science and Technology (KNUST) campus using the Delta Digital Photogrammetric Workstation (DDPW). The satellite images obtained at the scale of 1:2500 from the internet through the Google Earth software were loaded into the DDPW. Georeferencing was performed on each abstracted image using ground controls obtained with a geodetic standard Global Position System (GPS) receiver and, finally, map features were digitized in the DDPW. The digitized work was then exported into Computer Aided Design (CAD) software for further editing. Closed-loop traversing was done with a Total Station to provide base data for accuracy checks. The Relative Positional Errors (RPE) were analysed for three scenarios as Google-derived map versus Ground Survey, Survey and Mapping Division (SMD) map versus Ground Survey, and Google-derived map versus SMD map. The results demonstrated efficiency of mapping with Google images at the scale of 1:2500 for planimetric features at ground level only, and in respect of mapping at 1:5000 for features at ground level and up to the level of a single-storey building.
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