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Posted by Thomas Homan on December 12, 2006, 4:37 pm
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Hi Marc,
Look at http://www.ngs.noaa.gov/faq.shtml under the section titled 'Where
can I find the transformations between versions of WGS 84 and the versions
of NAD 83 and the versions of ITRF. The base answer is that there is no
document or utility to readily convert between the various flavors of WGS84
and NAD83. Two of the main components of the change are crustal motion and
improved GPS observation densities/procedures/equipment.
Tom
> Hello,
>
> We use a very nice gps post processing package called GrafNav. I recently
> had some (very belated) training in it and was surprised to learn that
> wgs84 and nad83 aren't really coincident anymore, and haven't been for
> some
> time. Its hard to find any info about it but I have found this:
> http://www.geod.nrcan.gc.ca/faq_e.php#19
>
> Now I am on the hunt for a package or library that supports the different
> versions of wgs84. I don't think its as simple as defining a new datum in
> your favorite tool, since the datum definitions always are relative to
> wgs84!
>
> The Geographic Calculator, as of 6.3, still considers them the same, as
> does GeoTrans 2.4.
>
> I'm looking for more info on this topic. It could very well be that I'm
> making a mountain out of a molehill, but we spend a lot of time and effort
> getting our positions as accurate as possible, and I need to know I've
> eliminated these sorts of static errors right off the bat.
>
> cheers
>
> Marc Pelletier
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