Newsline: May 2010

NGS Releases Survey User Guidelines for Real-Time GNSS Positioning; Interactive Tool Allows Geoid Height Comparisons and Canada-Wide DGPS Service to be Decommissioned in 2011.

NGS Releases Survey User Guidelines for Real-Time GNSS Positioning

NGS has released a document titled “National Geodetic Survey User Guidelines for Single Base Real-Time GNSS Positioning.” The guidelines provide definitive criteria to achieve various specific tiers of precision, with high confidence, using GNSS. Due to the plethora of variables associated with real-time (RT) GNSS positioning, a consistent, documented approach for using this technology to the best advantage was lacking. In preparing this publication, thousands of pages were researched to evaluate, refine and compile comprehensive information into an integrated form, thereby ensuring the most practical and reliable methodologies were developed for high-precision work.

The new document was developed to fill a void that exists for real-time GNSS positioning practitioners in two ways: It provides the background information necessary for RT users in the field; and it provides specific procedures and criteria to achieve 95 percent confidence with RT results

According to NGS, real-time GNSS positioning is rapidly becoming the favored method for obtaining centimeter-level coordinates and will continue as a dynamic technology due to advances in hardware and software, additional GNSS constellations, and new signals available to the user. NGS said that the guidelines will be updated as developments affect real-time procedures and data. For more information, visit

Interactive Tool Allows Geoid Height Comparisons

The U.S. Geoid 2009 Web site now features an interactive lookup for comparing new and old geoid heights. The new heights are also now being displayed on NGS’s Online Positioning User Service (OPUS) extended solution reports. Planning for the new U.S. vertical datum is in its early stages, and more details will be discussed at an NGS-led Federal Geospatial Summit this month. According to NGS, the new height system will make official elevations more easily and reliably accessible, thereby benefitting a multitude of geospatial applications. Orthometric heights determined using GEOID2009 (and future such models) will provide increasingly accurate estimates of true orthometric heights. Such a system will be consistent across the United States and its territories and represents the future of height determination. The U.S. Geoid Web site is

Canada-Wide DGPS Service to be Decommissioned in 2011

Canada-wide DGPS Service (CDGPS) will be decommissioned by March 31, 2011. According to Natural Resources Canada (NRCan), the free GNSS augmentation service has been broadcasting continuously since Oct. 14, 2003, over SkyTerra’s MSAT communication satellite. However, SkyTerra plans to launch MSAT’s replacement, SkyTerra 1, between August and October of this year. Transitioning to a new satellite would require an investment in new infrastructure beyond the scope of the Canadian Council of Geomatics. Additionally, the availability of commercial correction services and other alternatives to CDGPS has reduced the need for a government-provided free service, leading to the decision to cease operation of CDGPS next year.

NRCan said that it remains committed to the generation and improvement of its GPS C correction beyond that date. For more information, visit

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