Continuously Operating Reference Stations (CORS): Transformation Between KPLC CORS System And The Kenya National Geodetic System

Abstract

Advances in GNSS technology such as multiple constellation, receiver capability, improved software as well as new measurement techniques have increased the applications of GNSS in positioning. The need to continuously observe and measure using GNSS technology has led to the installation of Continuously Operating Reference Stations (CORS) around the world that provide real-time and accurate positioning for geodetic and other applications. In Kenya, several organizations have installed CORS for improved location accuracy in support of their operations. Kenya Power and Lighting Company (KPLC) is one such organization, currently with 15 CORS stations installed at various sites across the country. KPLC uses its CORS primarily to improve the accuracy of data in support of geospatial data management for its utilities. The KPLC CORS has the potential to support surveying within the company and beyond and thus can potentially generate more revenue to the company. To achieve this, it is necessary to establish the transformation parameters between the KPLC CORS Coordinate system (ITRF 2008) and the Kenya national geodetic system (UTM Arc 1960 datum) which is the official datum for surveying and mapping purposes. In addition, knowledge of transformation parameters between the two systems will make it possible for datasets in the two systems to be used on a common GIS environment through appropriate transformations. Six sets of coordinates of common points in the two systems were used to compute the transformation parameters using the Bursa-Wolf transformation. Coordinates data for the common points in the Kenyan geodetic system were acquired from the Survey of Kenya, while the coordinates in the KPLC CORS system were observed using geodetic quality receivers, post-processed and adjusted using KPLC CORS. The transformation parameters between the two systems comprising of three translations parameters, three rotation parameters and a scale factor were then determined. The translations in X, Y and Z axes were found to be -198.084m, -6.207 m and -10.275 m respectively, rotations about X, Y and Z axes are 1.21 arc seconds, 7.24 arc seconds and -6.16 arc seconds respectively, and the scale factor is 2.985 ppm. It was established that the differences in post-processing and adjustment results using a single CORS station and multiple CORS stations were small, averaging 0 ° 0' 0.0014 arc seconds in latitude, 0 ° 0' 0.0003 arc seconds in longitude and 0.025 m in height. The transformation parameters so determined needs to be tested for validity using test data, which was not available at the conclusion of the project. Further research involving more common points and a wider geographic extent is recommended.