GPS processing using online services

Online global positioning system (GPS) processing services have provided users with the opportunity to obtain freely high precision coordinates in a recognized datum. However, all services are dependent on the quality of the data and the length of data span supplied to them by the user. This study aims to assess the four globally available online GPS processing services from the point of view of a user wishing to take advantage of such a service for datum realization. Data from eight selected international GNSS service stations have been processed by each service and the results have allowed a statistically significant comparison analysis to be performed. Although users can expect a variability of results from different services when processing identical data, solutions with 24 h data are generally repeatable at the 1-2 cm level and accurate in terms of international terrestrial reference frame coordinate recovery at the 3-4 cm level. Such differences are accentuated as observation time decreases. Finally, postprocessing kinematic data, currently performed by only one online service, is a valid option for users provided they ensure data quality. DOI: 10.1061/(ASCE)0733-9453(2008)134:4(115) CE Database subject headings: Global positioning; Geodetic surveys; Datum; Accuracy.