Planimetric Accuracy Assessment of Digital Spatial Data for Urban Land Cadastral Registration: Case of Werabe Town, Ethiopia

Abstract

Planimetric accuracy, is a common way of expressing the quality of a spatial data set, it describes the accuracy of positions of spatial features by coordinates of a parcel in (x, y) direction. The main objective of this study is to assess the planimetric positional accuracy of digital orthophoto image and its extracted line map generated parcel features of Werabe Town. There are four basic data used to assessed planimetric(positional) accuracy, those are Geo referenced digital orthophoto, digital line map, GCP and Real-Time-Kinematic GPS (RTK GPS) in situ measured data. Data collected from silite zone urban Development and construction office and from Werabe Town. Collected coordinates of parcel corner and selected check points from well-defined and easily identifiable both on the imagery and on the ground used in RTK GPS. Extracted and the same points in situ RTK GPS measured parcel corner coordinates and check point evaluated in standard error estimation techniques of root mean square error. The orthophoto RMSE of easting and northing direction is 18.5 cm and 19 cm respectively and the overall RMSE of orthophoto is 26.5cm with o.45m (45cm) at 95% confidence level. The digital line map extracted coordinates and RTK GPS measured comparison results of the root mean square error of easting and northing direction is 50.2cm and 48.4cm respectively and the overall RMSE of orthophoto is 69.7cm with 1.2 m at 95% confidence level. Therefore, the conclusion of this study indicates that, the orthophoto planimetric accuracy assessment of 20 check points based on national accuracy standard for legal cadaster No 03/2015 is applicable for urban land spatial registration and large-scale mapping production. Because this standard state that overall planimetric accuracy is not exceed 40cm. In the case of digital line map parcel corner coordinates assessment result of the overall root mean square error is more than 40cm, according to national accuracy legal cadaster standard No 03/2015 is not applicable for urban land spatial registration and large-scale mapping production. However, the planimetric accuracy of digital line map does not satisfy national standard and it needs some improvement to use urban land spatial features registration and large-scale mapping in the Werabe Town.