Upcoming GRAV-D webinar

> Details and registration info here:
>
>> http://www.ngs.noaa.gov/corbin/class_description/GRAVD_0511.shtml

Thanks for the note on what I have no doubt will be an illuminating web-based seminar, Mike, but shouldn't you have started by asking "What does gravity mean to you?"

Howdy Mr. McMillan:

Not sure what you mean. As for the notion behind GRAV-D, I like the explanation offered by the Geodetic Survey Division in Canada who committed to the same goal before the US NGS. See below.

Having never liked dealing with differential leveling and being involved in all aspects to a limited extent, I welcome the new approach. I remain ignorant of whether there are plans to somehow support users by developing methods to transform between the current and new vertical datums.

Enjoy,

Canadian Spatial Reference System

A Gravimetric Geoid Model as a vertical datum in Canada
Marc Véronneau, Robert Duval and Jianliang Huang Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario marcv@nrcan.gc.ca

Abstract

The need for a new vertical datum in Canada dates back to 1976 when a study group at the Geodetic Survey Division (GSD) of Natural Resources Canada investigated problems related to the existing vertical reference system (CGVD28) and recommended a redefinition of the vertical datum. The US National Geodetic Survey and GSD cooperated in the development of a new North American Vertical Datum (NAVD88). Although the USA adopted NAVD88 as its datum in the early 90s, Canada did not follow suit because unexplained discrepancies of about 1.5 m were still present between east and west coasts. GSD continued to maintain and expand the vertical datum using the spirit levelling technique; however related cost and inherent deficiencies to this technique has forced GSD to rethink its approach for the delivery of the height reference system in Canada. Meanwhile, advances in space-based technologies and new developments in geoid modelling have emerged and now offer an alternative to spirit levelling. A new project to modernize the vertical datum is currently in progress in Canada. GSD is planning the adoption of a geoid model as the new vertical datum, which will allow users of space-based positioning technologies access to an accurate and uniform vertical datum everywhere across the Canadian landmass and surrounding oceans. Furthermore, this new vertical datum will be less sensitive to geodynamic activity, local crustal uplift and subsidence, and deterioration of benchmarks.

*Download PDF [PDF, 4.1 Mb, viewer]

> Not sure what you mean. As for the notion behind GRAV-D, I like the explanation offered by the Geodetic Survey Division in Canada who committed to the same goal before the US NGS. See below.

I'm afraid I was riffing on a recent message board trend. :>

> Having never liked dealing with differential leveling and being involved in all aspects to a limited extent, I welcome the new approach.

Yes, I am certainly not a large-scale differential leveling enthusiast. That and blue topping are for others to occupy themselves with. I welcome the new approach.