Journal of Basic and Applied Engineering Research Print ISSN: 2350-0077; Online ISSN: 2350-0255; Volume 2, Number 8; April-June, 2015 pp. 604-609 © Krishi Sanskriti Publications http://www.krishisanskriti.org/jbaer.html Adjusting of Absolute Point Positioning Accuracy Mohamed A. Youssef 1 , A.M. Abdel Hamid 2 and A.A. Elashiry 3 1 Mining and Metallurgical Engineering Department, Faculty of Engineering, Assiut Uni., Egypt 2,3 E-mail: Civil Engineering Department, Faculty of Engineering, Beni-Suef Uni., Beni-Suef, Egypt. 1 aburakm@yahoo.com, 2 amonged@yahoo.com, 3 eng_ahmedashiry@yahoo.com Abstract—In this paper, some trials were done to increase the positioning accuracy using one unit of GPS receiver. Firstly, the positioning accuracy improved from 40 to 20 m when errors correction models have been used, except ionospheric model. Secondly, the ionospheric error was studied relative to the other GPS errors, and it was founded a good relation (Empirical equation) between the ionospheric error and the earth rotation with correlation coefficient 99.4%. The usage of this relation improved the accuracy to 10m; which means that this relation is not accurate enough to predict the ionospheric error. Thirdly, a new positioning method , called (interpolation relative positioning), has been done by observing a fixed point in the observation area and moving in a short time , 5 minutes , to the unknown point. The resulting accuracy from this is improved to 50cm. Finally, a modification has been done on the previous method which returns to the fixed point to observe it again in a short time. This method called as (Extrapolation Relative Positioning), because the dependent mathematical technique is extrapolation technique. This method improved the accuracy to 20cm at short time equals 8 minutes. Keywords: GPS, Absolute Positioning, Interpolation and Extrapolation Relative Positioning, 1. INTRODUCTION There are several sources of error that degrade the GPS position from few meters to tens of meters [1]. These error sources are orbital errors: ionospheric and tropospheric delays, satellite and receiver clock errors, multipath, biases, and cycle slip [2]. GPS positioning can be classified into two positioning techniques: absolute and differential positioning (Fig. 1). The Absolute Point Positioning (APP) uses one unit receiver to determine the coordinate positioning, but due to the affected errors, this mode has a bad accuracy, if there is any correction method for it [3]. In the differential GPS Positioning (DGPS), two or more receivers are used to measure the same satellites at the same time, where one receiver occupies and observes the known point and the other receiver occupies and observes the unknown point. The coordinates of the unknown points are determined relative to the coordinates of the base station; therefore most of the errors can be eliminated or reduced through the differences. The accuracy in this method can reach to centimeters from baselines less than 20 km [4]. Fig. 1: GPS positioning techniques (a- APP technique and b- DGPS technique) Absolute Point Positioning (APP) is much economic and easier than DGPS, because it uses one unit receiver. It has two levels from positioning Service according to accuracy; Standard Point Positioning (SPP) and Precise Point Positioning (PPP) [5 and 6]. The first technique, SPS, uses the broadcast ephemeris data in estimating the receiver position [4, 7 and 8], where its accuracy about 40m [9, and 10]. The second technique, PPP, was proposed for the first time in 1995 by Heroux and Kouba. It performs position determination by processing un-differentiated dual frequency code and carrier-phase measurements from a dual-frequency receiver coupled with precise GPS orbit and clock products. It has been widely demonstrated that it is capable of providing accurate position solutions at sub-decimeter level for kinematic positioning and at sub-centimeter level for static positioning [11, 12 and 13]. These precise products have been supplied by the International GPS Service (IGS) since 2000 [14]. Over the past fifteen years, a number of researchers and engineers had developed the Single Point Positioning technique and its applications. Alkan. R. M. [2002] was studied the variation on navigation coordinates without Selective Availability (SA) and the advantages of removing SA to single point positioning accuracy , where an accuracy in some position , from 15 to 25 meters , was achieved [9]. El- Rabbany [2002] was presented a number of GPS point positioning approaches: firstly, by using the ionosphere-free code with broadcast ephemeris as the accuracy was about 10- 15m; secondly, by using the ionosphere-free code with precise ephemeris and clocks as the accuracy was about 5-10m; finally, by using the IGS network with final precise ephemeris and clocks as the accuracy was little than 1m [3]. Mosavi, M. R., et. al., [2013] were estimated the receiver position using