Assessment of Horizontal Positional Accuracy of Digital Orthophoto in the Town of Chiro, Ethiopia
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Date
2021-09
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Addis Ababa University
Abstract
Positional accuracy is a matter of renewed concern and it deals with the accurateness of the location of map features, and measures how far a spatial feature on a map is from its true or reference location on the ground. A crucial component to examine an effective positional correctness of digital spatial data needs acquisition of better quality of independent ground reference data. This data makes spatial analysis less troublesome and enables better decision making. The objective of this thesis is to examine the horizontal positional accuracy of digital orthophoto. Accordingly, the study used in-situ Global Navigation Satellite System (GNSS) data to validate the accuracy of horizontal coordinates an Orthophoto located in Chiro town. GNSS data is observed using Leica GS 14 Differential Global Positioning System (GPS) instrument and post processed with different processing software’s like Leica Geo-Office (LGO) and online processing software’s using AUSPOS and OPUS with a tie to local and regional GNSS reference stations to obtain horizontal coordinates. In this paper the accuracy of horizontal coordinates of Digital Orthophoto was evaluated by comparing with the corresponding coordinates measured directly from in-situ GNSS data. As a result, the root mean square error between the orthophoto coordinates and in-situ GNSS coordinates of the nine check points in x and y-directions are 0.993 m and 1.462 m, 0.718 m and 1.712 m, 0.715 m and 1.709 m as compared to the GNSS data obtained from LGO, AUSPOS and OPUS processing respectively. In addition, the orthophoto horizontal accuracy was found to be 3.059 m, 3.213 m, and 3.206 m at 95 percent confidence level as compared to the GNSS data obtained from LGO, AUSPOS and OPUS processing respectively. Therefore, it can be concluded that, in all condition the accuracy of orthophoto doesn’t meet the national standard of error budget (30cm) for the purpose of Standard Mapping work use. Rather, it can use for Visualization and less accurate work use. In its present state, it can be used for a Master plan and General Economic development plan application.
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Keywords
GPS, GNSS, LGO, AUPOS, OPUS, Digital Orthophoto, Standard Mapping, Visualization, Master plan, General Economic Development plan