[Taxacom] GPS units that record the time a waypoint was taken, accuracy, datum

[Arthur Chapman]

Here are some references worth looking at for Position shifts for 
different Geodetic Datums

http://www.colorado.edu/geography/gcraft/notes/datum/gif/shift.gif

Also see the table on page 24 of the Biogeomancer Guide

http://www.gbif.org/prog/digit/data_quality/BioGeomancerGuide


Arthur

Bob Mesibov wrote:
> Hi, Karl.
>
> Yes, the datum can matter. Here in Australia the shift from AGD66 to
> GDA94 a few years ago was ca. 200m, which is more than 10x the accuracy
> now expected of hand-held GPS units.
>
> When I was getting initial feedback on my website on spatial data basics
>
> http://www.utas.edu.au/spatial/locations/index.html
>
> in 2005 I found to my amazement that some recorders thought the datum
> shift only applied to UTM coordinates, and that lat/long was unaffected.
>
> Another problem has been that many recorders use the printed,
> UTM-gridded 1:25000 map series in Tasmania. This older series is based
> on AGD66, hence is ca. 200m off the UTM reading for the same spot on a
> GPS unit. I'm sometimes asked, 'Which is right?'
>
> I agree with Finn that databases and publications should include datums
> with records. See also the GBIF publication on best practice in
> georeferencing:
>
> http://www.gbif.org/prog/digit/Georeferencing
>
> It's also interesting to see published location data given to so many
> decimal places that the bird/tree/nest has apparently been located to
> the nearest 1 mm, which is what happens when you mindlessly transcribe
> what appears on the GPS screen.
>