Sometimes when doing GPS field work I will often require a way to double check my own GPS Processing work or am sometimes too far from an active control network to tie into. Using Precise Point Positioning or PPP service in these situations has often come to my aid, especially on jobs in Nunavut or in Northern Ontario.
Natural Resources Canada’s Canadian Geodetic Service provides a free online global GPS processing service called Canadian Spatial Reference System – Precise Point Positioning (CSRS-PPP), where you can process files containing RINEX (common Receiver Independent Exchange Format that is used to exchange GPS data between various software and hardware) observations from either a single or dual frequency receiver in either static or kinematic modes. The service is free but does require that you sign up to obtain a username and password to gain access.
Once logged in, you upload your GPS file and basic info, then you will receive an email containing corrected coordinates (latitude, longitude, ellipsoid height) in either NAD83(CSRS) or the ITRF reference system. It also applies the HTv2.0 height transformation and produces orthometric heights compatible with CGVD28 elevations to your data.
PPP results generally are more accurate when recorded over a span of several hours, so I tend to let my receivers run longer if I know that will be using PPP.
“PPP accuracy improves with the length of the data collection period. A minimum period of good quality GPS data is required to permit convergence and resolving ambiguities which in turn can improve the accuracy of the entire dataset. The minimum period and the accuracy attainable will depend on the type of GPS equipment, the site (multipath, obstructions) and atmospheric conditions. Extending the data collection past this minimum period should further improve accuracy, but more so with dual-frequency receivers than with single frequency”. See http://www.geod.nrcan.gc.ca/products-produits/ppp_acc_e.php for more information.
The Canadian Geodetic Service have also created a PPP Direct utility for Windows 7 (note: I have not tested it yet) where you can Submit your GPS data for PPP processing without logging on to the web site. The PPP Direct utility lets you ‘drag and drop’ RINEX files onto an icon where it is then immediately submitted for CSRS-PPP processing (so an internet connection is required).
The login to begin PPP processing or to download the PPP Direct utility installation file is http://www.geod.nrcan.gc.ca/online_data_e.php and a detailed PPP handbook covering all the basics of the service can be found here http://www.geod.nrcan.gc.ca/userguide/pdf/howtouse.pdf