flavours of wgs84

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

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




--
Posted via a free Usenet account from http://www.teranews.com

On Tue, 12 Dec 2006 14:37:27 -0700, "Thomas Homan"



Actually there's HTDP that covers these transformations in the United
States. It isn't clear to me whether it covers the rest of North
America.



--
Chuck Taylor
http://home.hiwaay.net/~taylorc/contact/

Thanks, this tool does exactly what I was looking for. The interface is
painful, but sourcecode is available. I may polish up my Fortran skills and
turn it into a dll I can call it from elsewhere.

A private responder also pointed me to
http://nauticalcharts.noaa.gov/csdl/Vdatum_data/VDatum106.pdf
which contains a very good discussion of the issues in sections 7 and 8.

Blue Marble tech support tells me that they do support the various versions
of ITRF, which are functionally equivalent to the wgs84 versions.

Thanks everyone,

Marc