Browsing by Author "Sisay, Walelign"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Horizontal Positional Accuracy Assessment of an Orthopohoto: A case of Addis Ababa City
    (Addis Ababa University, 2019-06) Sisay, Walelign; Tulu, Besha (PhD)
    This study tries to examine horizontal positional accuracy of orthophotoof Addis Ababa city using in-situ Global Positioning System (GPS) data. GPS data is processed using different processing systems like spectrum survey, Leica GeoOfice(LGO) and also online processing systems AUSPOS and OPUS in a least square sense with a tie to local and regional GPS reference stations to predict horizontal coordinates at twenty checkpoints to assess the accuracy of orthophoto. The accuracy of horizontal coordinates of the checkpoints derived from orthophoto was evaluated by comparing it with the corresponding coordinates measured directly from in-situ GPS data. When we compared the orthophoto with that of online processing AUSPS it is in a good agreement with GPS data observed at twenty checkpoints with a root mean square error of 9.3 cm in x- and 9.9 cm in y-coordinates. On the other hand, the horizontal accuracy of orthophoto is determined at 3.19 cm as it compared with twenty check points with 95% confidence level. Whereas, when the GPS data are processed using sokkia spectrum with a tie to local GPS reference station the horizontal coordinates of the orthophoto are in agreement with in-situ GPS coordinates at an accuracy of 7.2 cm and 21.39 cm in x and y-directions respectively, The finding of the result illustrates that the horizontal accuracy of orthophoto is determined at 8.81 cm with 95% confidence level, while the GPS data is processed with a tie to local GPS network. Therefore, it can be concluded that, the accuracy of the orthophoto is within the national standard of error budget (~ 25cm).