IRJMST Vol 7 Issue 1 [Year 2016] ISSN 2250 – 1959 (0nline) 2348 – 9367 (Print) International Research Journal of Management Science & Technology http://www.irjmst.com Page 29 Comparative Study of Online GPS Post Processing Services and Effects on DGPS Data Processing *Manas Kumar Jha, **Saurabh Singh, **Nisha Upadhyay, *** Nishant Khare *Manager (GIS), IL&FS Environmental Infrastructure & Services Ltd. **M.Tech. (Geomatics), Indian Institute of Surveying and Mapping, Survey of India, Hyderabad, India ***M.Tech. (Spatial Information Technology), Devi Ahilya Vishwavidyalaya Indore, India Abstract: Increasing dependency on Differential Global Positioning System (DGPS) survey for accurate surveying and mapping project is common across the globe. Whether someone require a point data or want to align the LiDAR scans or point cloud data the precise DGPS value is very much required. The precision in the accuracy of the DGPS value determines the overall accuracy of the project output. To achieve a considerable accuracy DGPS survey methodology and its post processing technique must be defined beforehand. DGPS data acquisition in RTK (Real time kinematic) and PPK (post processing kinematic) is common in survey projects. The objective of processing of DGPS data in both RTK mode and PPK mode is to transform the absolute positioning of a point (X, Y, Z) in a relative positioning with reference to the other point of a known coordinates in a similar reference system. This paper will discuss in details the comparison of DGPS processing output using the software based post processing where control points get validated using various online internet based GPS processing services. Keywords: Global Positioning System, DGPS, RTK, Post Processing, GNSS, Accuracy Assessment, Surveying, Post Processing. Introduction: Traditionally in geodesy and surveying, the measurements are collected over temporarily or permanently monumental points and stored for data-mission processing. In many cases, the position of the user’s antenna has to be determined in real time such as navigation or mobile mapping. Real time determination of position involves wireless transmission system over radio frequencies, and L-band or C-band geo-stationery satellites for coverage for entire continents. Depending on the accuracy requirements, two modes of real-time operation can be used: DGPS or RTK. DGPS [1] requires a reference station receiver transmitting pseudo range corrections to the users, whose receiver use this information together with their measured pseudo- ranges for positioning at the meter to few centimeter accuracy levels. RTK [2] on the other hand, is based on transmitting reference station carrier phase data to the user’s receivers. In its simplest form, a DGPS reference receiver is set up at a site with known coordinates. After it has been configured to operate as the `base station’, the reference receiver tracks continuously all the visible satellites and determines the corrections necessary for its pseudo range data to be able to compute the Single Point Positioning (SPP) [4] result that is identical to the known coordinates of the site. There are two methods of GPS (Global Positioning System) data processing. These are Post-processing and Real-time Processing. The Post-processing [3] method of involves downloading of complete survey data and processing in office using various software such as Trimble Business Center,