Thursday, February 11, 2010

Part 2 WGS-84 What is it? Current world GPS status

WGS-84 Part 2
Oblate Spheroid


In Part 1 of WGS-84, I stopped at the point where I wrote the Russian Global Navigation Satellite System (GLONASS) is referenced to the PZ-90 geodetic model.  The WGS-84 geodetic model as well as the PZ-90 geodetic model are really both descriptions of the shape of the earth.  The earth is not a perfect sphere but has ellipsoid characteristics. In order to attain the highest accuracies using the satellite navigation systems, the shape of the earth must be taken into account.  As a result of the development through the years of more and more accurate measurements being made, the geodetic models have achieved unheard of accuracies.
  Now, what is the difference in location accuracy between  the PZ-90 (Parametri Zemli 1990 (PZ-90, or in English translation, Parameters of the Earth 1990, PE-90) geodetic datum, standard and the WGS-84 standard? 
The difference between the coordinates of points on earth in WGS 84 and PZ-90 has been found to be less than 15 m (average: 5 m). As I said in my previous post, "not much". I know that you have been advised to not rely on your GPS receiver while flying in non-WGS 84 countries.  It is certainly not permitted to utilize your GPS for approaches.
The Russians have made a strong commitment to completing their Global Navigation Satellite System (GLONASS) with their most recent launch of 3 new modernized "M"satellites on December 14,  2009. They presently have plans to launch 5 additional satellites in 2010 completing the constellation of 24 satellites.  The system should achieve full operational capability near the end of this year.
The manufacturers of GPS receivers are aware of the need to supply receivers capable using both GPS and GLONASS signals as well as European Galileo signals.  The buzz word of "interoperability" is flowing through the GPS community presently. Novotel and Thales both make available receivers today capable of using both sets of signals.  


More to come in Part 3 of WGS-84 What is it?

If any of you who read this flies into Russia, I would appreciate your comments on your real world experience concerning your observations on the accuracy of your GPS guidance.  Are you able to notice any difference when looking out your window? Please feel free to comment on the blog.
Thanks!
Dick

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