[Qgis-user] Re: off topic, wgs 84 datum

[M.E.Dodd]

A naïve question, what if you are doing a long-term experiment and need to return to the same position say every 20 or 50 years to within a couple of cm how will this be affected?  Already positions we recorded 25 years ago have moved significantly due to continental drift but can account for this, how do all the little tinkerings with the same datum affect things? 

-----Original Message-----
From: Gerry Creager [mailto:gerry.creager at tamu.edu] 
Sent: 04 November 2010 11:13
To: mtnbiketrail at zzz.com
Cc: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Re: off topic, wgs 84 datum

mtnbiketrail at zzz.com wrote:
> this wiki entry says wgs 84 is to become obsolete??
> 
> http://en.wikipedia.org/wiki/WGS84#cite_note-0

At the risk of humor, datums are ephemeral. However, NAD83, and for that 
matter, NAD27 and Pulkovo 1942, are still with us. Periodic adjustments 
may, or may not, result in renaming the datum in some way. For instance, 
NAD83 was updated and adjusted once every 4 years until computational 
and data management systems allowed it to be updated much more 
frequently and less painfully. Now, the adjustment is annual, by 
unnoticed by most users. Similarly, WGS84 has been adjusted annually. At 
some point a new objective survey of control will be called for and a 
new datum will be created. I don't anticipate a big change in our usage, 
though.

-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
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