Geodesy and Geomatics

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http://etd.aau.edu.et/handle/12345678/188

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Browsing Geodesy and Geomatics by Author "Andinet, Ashagrie (Mr.)"

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    Horizontal Accuracy Assessment of Digital Aerial Photograph in Urban Cadaster: The Case of Wereda 10, Gulelie Sub-City, Addis Ababa
    (Addis Ababa University, 2018-10) Azeneg, Eneyew; Andinet, Ashagrie (Mr.)
    Positional accuracy deals with the accuracy 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. This research focused on the following problems: Coordinate shifting, area variation and shape difference between the ground measurement, line maps and digital aerial image. The main objective of this study is to assess the horizontal position accuracy of aerial photogrammetric image generated coordinates of Wereda 10, Gulelie sub city. There are three basic data sources used to assess horizontal accuracy assessment: Such as Geo referenced digital aerial photograph, digital line map and GPS data. This research contains the following steps: First step created twenty sample GCP points by using static GPS. The seconded step is process sample GCP points by using Leica Geo office combined software. While, the third step is measured hundred parcel corners points by using RTK GPS as a reference used the established GCP points. In addition, the fourth step is digitized parcel corner points and polygons from aerial photograph and digital line map. Finally, assessed horizontal accuracy, standard deviation, means value, minimum and maximum values. The paper describes the visualization possibility of estimated results of horizontal positional accuracy of digital aerial photographs and established cheek points and area, side length and coordinates comparison for digital aerial image and digital line map based on RTK GPS. The root mean square error results of twenty check points and digital aerial photograph the easting and northing component is 18.1cm and 18.8cm, respectively. The RTK GPS and aerial image comparison coordinates results show that the root mean square error of easting and northing component is 37.6cm and 38cm respectively. The RTK GPS and digital line map coordinates comparison results show that the root mean square error of easting and northing component is 39.2cm and 39.8cm respectively. The root mean square error is 5.828 m2 and 5.852 m2 in aerial photograph and digital line map respectively. The root mean square error is 38.1cm and 40 cm in aerial photograph and digital line map side lengths respectively. Therefore, these variations come from different factors: Such as shadows, topographic factors, vegetation covers and there are some limitations to these techniques as it solely on visual interpretation.
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    Modeling of Street Address Using Multiple Reference Geocoding and Address Point Technique. A Case Study of Yeka Sub City, Addis Ababa, Ethiopia
    (Addis Ababa University, 2019-02) Worku, Mammo; Andinet, Ashagrie (Mr.)
    Addresses are the essential means by which people tried to conceptualize geographical position features using streets and accessibility is the ultimate goal of street address. Poor street address results in a serious challenge in terms of substantial loss of accessibility, less aware for usage, and impracticable for services deliberation to achieve social integration. This comes true for under implementation of street address as pilot project in Addis Ababa City. The aim of this research was made on the street address modeling based on multiple reference geocoding and address point technique. Focused group discussion and field survey was conducted on the identified factors and spatial document analysis was applied to generate street address model. The model geocoding involves entity relation and physical diagram analysis, roundabouts Euclidian and street analysis, and codification of address elements. In addition, Four algorithms were explored, evaluated and integrated with address point analysis. Also, comparison and conceptual framework analysis for party-centric data usage were made. Results indicated that reference points, streets, entrances, parcels, buildings, floors, and floor sections are the basic street address elements which can be linked with the owners. Based on the indicator and Euclidian analysis of four roundabouts, CMC roundabout has the highest proximity result for the study area. Street network infrastructure rates 24.9% while built-up, non-built-up and others occupy with a sum of 75.1% in the landscape of the study area. Among those streets, 29.1% of them are classified as sub-streets while 1.2% of them were classified under the path. The analysis made on the exploration of centroid algorithm revealed that, of the total four algorithms, the biggest inscribed circle method has a 97.5% match rate and the centroid was fit 100% inside the polygon. The comparison results depict that the new model was more user-friendly, comprehensive, and navigable than existing one. This is to mean that the new model is integrated with the address point to simplify the address geocoding, and supports a conceptual framework model of an improved navigation system which is analyzed under this research.
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    Planimetric Accuracy Assessment of Digital Spatial Data for Large Scale Planimetric Mapping: The Case Study on Dire Dawa City, Ethiopia
    (Addis Ababa University, 2018-11) Ephrem, Mulugeta; Andinet, Ashagrie (Mr.)
    This study assesses the planimetric (x, y) accuracy of digital spatial data used for mapping large scale planimetric maps in Dire Dawa city. These digital spatial data are Orthophoto and its line map (parcel and road center line) and Worldview-1 panchromatic satellite image. RTK GPS measurement technique was used as an independent source and point wise method were used to assess the planimetric accuracy the digital spatial data set. Due to unavailability of local CORS station which used as a reference during RTK GPS measurement second order GCPs which was established by E.G.I.A (Ethiopian Geospatial Information Agency) was used as a base station. But before conducting RTK GPS survey a 12 hour static GPS survey were conducted on selected two second order and one first order GCP established by E.G.I.A and the GPS data are processed with a tie to IGS CORS station found in Addis Abeba and two free online GPS data processing service provider that are AUSPOS and OPUS. For accuracy comparison OPUS processed coordinates result were taken. However, the positional accuracy of selected GCP has mean error of -0.77m and 2.4m on x and y direction respectively. Therefore due to discrepancy of coordinate obtained from E.G.I.A and processed coordinate planimetric accuracy of orthophoto was assessed twice for selected 20 points with reference to RTK survey coordinates computed from E.G.I.A GCP and computed coordinate from IGS station. The planimetric accuracy of orthophoto relative to GCP established by E.G.I.A has good accuracy than coordinate computed from current derived coordinate from IGS station. Based on this relative to E.G.I.A GCP the planimetric accuracy orthophoto for the selected 20 points has RMSE of 0.138m and 0.15m on X and Y direction respectively and with respect to computed coordinate the planimetric accuracy of orthophoto has RMSE of 0.67m and 2.498 on X and Y direction respectively. Thus to increase the significance and applicability of this study finding the remaining line and polygon feature of orthophoto and its line map and satellite image derived coordinate compared with RTK survey coordinate correction computed from reference E.G.I.A second order GCP. Therefore the planimetric accuracy of orthophoto for the selected parcels, line and points are computed separately relative to RTK survey results thus the RMSE of these feature lie between 0.138m-0.22m and 0.12m – 0.24m on x and y direction respectively and 95% confidence level lie between 0.37cm and 0.55 cm and the planimetric accuracy of digital line map (parcel) RMSE are 0.173m and 0.196m on x and y direction respectively and 0.45m with 95% confidence level. The digital line map (road center line) also assessed its planimetric accuracy relative to coordinates obtained from RTK GPS survey coordinates and has RMSE of 0.148m and 0.191m on x and y direction respectively and 0.41m at 95% confidence level. Similarly the planimetric accuracy of worldview-1 satellite image assessed on similar sample parcel and line (flood protection fence) feature with that of orthophoto. Thus planimetric coordinates extracted from selected sample feature from satellite image are compared with Coordinates obtained from RTK GPS survey on similar feature. Based on this parcel feature has an RMSE of 1.73m and 2.06m on x and y respectively and 4.67m at 95% confidence level. The planimetric accuracy of line feature (flood protection fence) has RMSE of 1.89m and 2.25m on x and y direction respectively and 5.09m at 95% confidence level. The planimetric accuracy assessment result obtained from orthophoto and its digital line map based national accuracy standard for legal cadastre 03/2015 and ASPRS international digital spatial data set accuracy standard are applicable for large scale urban cadastral map and . However the planimetric accuracy of worldview-1 satellite image is not applicable for large scale cadastral map production.
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    Vertical Accuracy Assessment of Open Source Digital Elevation Model Using GPS Point and Reference Dem Over Ethiopia A Case Study In Addis Ababa And Dire Dawa
    (Addis Ababa University, 2018-11) Abdi, Ibrahim; Andinet, Ashagrie (Mr.)
    Digital elevation model (DEM) is a digital representation of the surface topography of the earth. Apart from visualization of o 3D surface topography of the earth, DEM is very useful data source to perform various analyses. DEM can be generated from wide range sources including land survey, Photogrammetry and remote sensing satellites. SRTM 30m DEM by The Shuttle Radar Topography mission (SRTM), the global digital elevation model by Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER GDEM) and a global surface model called ALOS Worldview 3D 30 meter (AW3D30) by Advanced Land Observing Satellite (ALOS) are satellite based global DEMs freely available, open source DEM datasets. The specified accuracy of these dataset is often uneven within each dataset due to various reasons including radar characteristics, type of topography in different regions and physical properties of the surface. This study aims to assess the vertical accuracy of ASTER GDEM2, SRTM 30m and ALOS (AW3D30) global DEMs over Ethiopia in two study areas-Addis Ababa and Dire Dawa by using DGPS points and other available accurate topographic reference data. The method used to assess the vertical accuracy of those DEMs range from simple visual comparison to relative and absolute comparisons providing quantitative assessment that used the elevation differences between DEM datasets and reference datasets. The vertical accuracy of DEMs assessed in three stages based on the reference datasets used. The first vertical accuracy test is done by taking the residual from elevation differencing between GPS points and DEM elevation values at the location of every GPS points. The result of this assessment showed better accuracy of SRTM 30m DEM (having RMSE of 5.14 m and 6.35 m in Addis Ababa and Dire Dawa Study areas), and closely followed by ALOS (AW3D30) DEM which scored RMSE of 5.34 m and 6.33 m in Addis and Dire study areas respectively. ASTER GDEM 2 showed the least accuracy by scoring RMSE of 13.27 m in Addis Ababa and 11.41m in Dire Dawa study areas. The second test was done by DEM (image) differencing (by subtracting every pixel of DEMs from every pixel of Reference DEM, which gives us the elevation residual). The result from this method assessment gave us RMSE values of 17.2 m, 4.5 m and 4.7 m in Addis Ababa for ASTER, SRTM and ALOS DEMs respectively; RMSE of 9.7 m, 5.43 m and 5.74 m in Dire Dawa Study area for ASTER, SRTM and ALOS DEMs respectively. This also shows the better accuracy of SRTM 30m DEM over the other two at least for this study. The third accuracy assessment was done by analysis of derived products such as slope and drainage network. This also resulted in better quality of derived products for SRTM and ALOS DEM than ASTER GDEM. This concludes SRTM 30m and ALOS (AW3D30) DEM can be used for slope classification and Drainage or watershed delineation in this regions.