The number of digits given is definitely is not a good substitution for this for many reasons, just one of which is that the the original may have been captured in a different coordinate system (such as degrees decimal minutes - the most precise coordinate system other than UTM or other meter-based systems when recording data from a GPS) and then converted to decimal degrees where the number of significant digits then becomes meaningless.
Happily, the Darwin Core also has a dwc:coordinatePrecision term (http://rs.tdwg.org/dwc/terms/index.htm#coordinatePrecision), which can say explicitly what the level of precision is in the coordinates given. The dwc:coordinateUncertaintyInMeters (http://rs.tdwg.org/dwc/terms/index.htm#coordinateUncertaintyInMeters) is supposed to account for all sources of uncertainty in the coordinates given, including GPS accuracy and coordinate precision.
For the sake of completeness, there are the terms dwc:pointRadiusSpatialFit (http://rs.tdwg.org/dwc/terms/index.htm#pointRadiusSpatialFit) to capture analytically how well the point-radius given matches the actual uncertainty of the coordinates given (in case someone artificially adds uncertainty), the dwc:georeferenceProtocol (http://rs.tdwg.org/dwc/terms/index.htm#georeferenceProtocol) to explain the method used to georeference, and the dwc:dataGeneralizations (http://rs.tdwg.org/dwc/terms/index.htm#dataGeneralizations) to explain what was done to the georeference post-facto to obscure it.
On Sat, Feb 26, 2011 at 4:04 PM, Peter DeVries pete.devries@gmail.com wrote:
Hi Bob, Yes an estimate of the precision / extent should be recorded by the original observer. This has been repeated several times and it is interesting that even TDWG did not incorporate this into their data collection. What I was proposing was a specific extension to the ietf proposal for occurrence records. It adds something very similar to pointRadiusSpatialFit to a latitude and longitude. By standardizing on the significant digits we gain something even before there is general software support for this standard. That records with "geo:41.53000000,-70.67000000;u=100" are an equivalent URN, while. "geo:41.53000000,-70.67000000;u=100" and "geo:41.53,-70.67;u=100" are not That allows those records to be linked within a triple or quadstore. As in this earlier example: Here is a browsable view of one of the areas bit.ly http://bit.ly/hBtVFL
http://lsd.taxonconcept.org/describe/?url=geo:41.53000000,-70.67000000;u%3D1... Without doing anything other than standardizing on the number of digits, occurrences attached to the same GPS reading are linked in both a triple store and a google search. Where as software needs to be written that interprets "geo:41.53000000,-70.67000000;u=100" and "geo:41.53,-70.67;u=100" as equivalent. Try Googling "geo:44.86294500,-87.23120400;u=10" If the ietf.org standard is supported in future versions of Virtuoso and other tools then we would not need to include the redundant use of geo:lat geo:long for the dynamic maps.
- Pete
On Sat, Feb 26, 2011 at 1:01 PM, Bob Morris morris.bob@gmail.com wrote:
Your arguably reasonable recoding of the geo uri's of your example illustrates an issue on which so much metadata is silent: provenance. Once exposed, it is probably impossible for someone to know how the uncertainty (or any other data that might be the subject of opinion or estimate) was determined and whether the data is fit for some particular purpose, e.g. that the species were observed near each other. BTW, the IETF geo proposal was adopted in 2010, in the final form given at http://tools.ietf.org/html/rfc5870%C2%A0. One interesting point is http://tools.ietf.org/html/rfc5870#section-3.4.3%C2%A0which says "Note: The number of digits of the values in <coordinates> MUST NOT be interpreted as an indication to the level of uncertainty." The section following is also interesting, albeit irrelevant for your procedure. It implies that when uncertainty is omitted (and therefore unknown), then "geo:41.53000000,-70.67000000" and "geo:41.53,-70.67" identify the same geo resource.
Bob Morris On Wed, Feb 23, 2011 at 4:56 PM, Peter DeVries pete.devries@gmail.com wrote:
[...]
- I added in my proposed "area" so that it is easy to see what species
were observed near each other. Since there was no measure of radius in these longitude and latitudes I made the radius 100 meters. Normally I would estimate the radius for a GPS reading to be within 10 meters but some of these observations were made where the GPS reading was taken and the readings were given only to two decimals. Area = long, lat; radius in meters following the ietf proposal but with the precision of the long and lat standardized example "geo:41.53000000,-70.67000000;u=100" [...]
-- Robert A. Morris Emeritus Professor of Computer Science UMASS-Boston 100 Morrissey Blvd Boston, MA 02125-3390 Associate, Harvard University Herbaria email: morris.bob@gmail.com web: http://efg.cs.umb.edu/ web: http://etaxonomy.org/mw/FilteredPush http://www.cs.umb.edu/~ram phone (+1) 857 222 7992 (mobile)
--
Pete DeVries Department of Entomology University of Wisconsin - Madison 445 Russell Laboratories 1630 Linden Drive Madison, WI 53706 TaxonConcept Knowledge Base / GeoSpecies Knowledge Base About the GeoSpecies Knowledge Base
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