The purpose of this software is to provide a GIS collaboration environment for the world over Internet, in which people can share and assess their measured GPS data. In other aspects, it would create and support a virtual community who is interested in GPS field. Many people are nowadays using GPS technology to know their position and to locate features (an example could be the Openstreetmap project). Unfortunately they usually do not have enough information about the real accuracy of the tools they use. By means of this software, expert users can distribute their high-accuracy DGPS data corresponding to specific points or paths. Those data are taken as reference (“the ground truth”) by the system. Besides, common users can evaluate their low-accuracy GPS receivers by analysis between appropriate DGPS data and their measured one. Thus, it can be used for education, in which students practice with GPS receivers and then assess the accuracy of their output data by DGPS one given by professors. For the presentation of data and calculation, interactive maps and related graphs are generated dynamically on-the-fly. Furthermore, the software contains statistic of accuracy estimation for each measurement corresponding to a GPS receiver, so related organizations and institutions can obtain a practical foundation for evaluation of each brand of GPS receivers.

This software is developed as web-based application with three-tier architecture, so after being installed, intended publics can access it over Internet easily. It is divided into 5 modules, which are User Management, DGPS and GPS data as POINT, DGPS and GPS data as PATH, Statistic, and Administration. User accounts are distinguished between Expert and Common groups, among which the former is granted full privilege. Handling data is one of the most critical parts of this software. Users are supported to upload data in NMEA, which is the output format of most of GPS receivers, so they do not need any pre-processing but they can use the recorded data immediately after measurement. Moreover, it also allows dealing with data in GPX format, which could be considered as a standard for the interchange of GPS data between applications and Web services on the Internet. The combination of PostgreSQL database with spatially-enable extension PostGIS as data tier and application of PHP Mapscript in logic tier creates a mechanism so-called Map Generation Engine, which produces interactive maps to present GPS data dynamically without any manual operations. Other applications as client can also access to maps via WMS, which is built in this software with conformation to OGC's implementation specification. The reference of those interactive maps is robust by making use of Google map as background layer. For the accuracy evaluation part, the buffer method is applied with the GPS and DGPS data as LINE while ellipsoid algorithm is used for data as POINT. In addition, users are asked to give information about their GPS receivers, which is consequently stored in a database and, in combination with assessed results, exploited for statistic about brands of device.

1. Tran Tho Ha - 2. Nguyen Thi Thanh Thuy