[Taxacom] Impossible geocodes

Dean Pentcheff pentcheff at gmail.com
Sat Jan 31 13:01:01 CST 2015

For those with an interest in these issues, an excellent document is:

Chapman, A.D. and J. Wieczorek (eds). 2006. Guide to Best Practices for
Georeferencing. Copenhagen: Global Biodiversity Information Facility.
Available online at http://www.gbif.org/orc/?doc_id=1288

It is full of well-explained technical information accompanied by
worked-out examples.

Dean Pentcheff
pentcheff at gmail.com
dpentche at nhm.org

On Fri, Jan 30, 2015 at 2:02 PM, <mesibov at southcom.com.au> wrote:

> Tom Schweich wrote:
> "The centroid of the points was shifted to the northeast about 1.5-2.0 m.,
> something I was unable to account for."
> Plate movement? I'm guessing your control points were survey marks in the
> local coordinate reference system, which moves with the plate. Here in
> Australia, survey marks are databased with the GDA datum, which is more
> than 1 metre different from WGS84 because the whole continent is moving NE
> at about 6 cm a year.
> "I went out on my bicycle and visited 7 control points 14 times each, and
> learned that my GPS receiver was accurate (on that day at that place) to
> between 4-5 meters"
> Excellent test. Have you checked to see how close Google Earth gets to the
> control point positions? On a well-georegistered image tile with a
> reasonably high-resolution image, Google Earth can do better than a
> handheld GPS.
> Not much help here in Tasmania under a tree canopy, though. Where in hilly
> terrain my GPS struggles to get an 'accuracy' declaration less than 20 m.
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