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Re: Best Way to Extend the Geo Vocabulary to include an "error" or "extent" radius in meters

From: Sean Gillies <sean.gillies@gmail.com>
Date: Mon, 11 Oct 2010 11:30:56 -0600
Message-ID: <AANLkTi=w-MjhiWDmuhLgoqSyiTLg4wH6XQ72q+7syVGN@mail.gmail.com>
To: Peter DeVries <pete.devries@gmail.com>
Cc: public-lod@w3.org

FWIW, there's precedent for point and uncertainty in the "geo URI" RFC:


This would let you express fuzzy locations with fuzzy points instead
of precise circles.


On Mon, Oct 11, 2010 at 10:52 AM, Peter DeVries <pete.devries@gmail.com> wrote:
> Hi Paul,
> Thanks for bring up these relevant issues.
> The geo vocabulary assumes the lat and long are in WGS84.
> One of the problems that we were seeing are records that were georeferenced
> to the center point of a Canadian Province at it was not clear if that was
> actually where the species was observed. Was it at that specific point
> or did someone simply tag apply geocode it later to the center of the
> province later? Part of this relates to your
> comment on provenance.
> I had hoped on incorporating both the extent "the actual area that was
> sampled" along with the error in the GPS reading to create one all
> encompassing radius. Sometimes people will take a GPS reading and then
> observe butterflies or plants that are not exactly at that point but within
> 50 to 100 meters.
> I am hoping that the issues that you mention with New York etc would be in
> part of a separate set of statements
> using some standard vocabulary like geonames to indicate the county or state
> the observation was made.
> Thanks Again,
> - Pete
> On Mon, Oct 11, 2010 at 9:47 AM, Paul Houle <ontology2@gmail.com> wrote:
>> On Thu, Oct 7, 2010 at 5:28 PM, Peter DeVries <pete.devries@gmail.com>
>> wrote:
>>> Hi LOD'ers,
>>> There was some discussion about ways to record species observations using
>>> the geo vocabulary at a recent biodiversity informatics meeting.
>>> Some see the advantages of using the geo standard, but we really need to
>>> have a way to incorporate and error or extent in meters.
>>     For Ookaboo I've worked out an internal data model for points;
>> Ookaboo also knows about real shapes,  but the fact is that most people out
>> there will throw points at you and only know how to consume points.
>>     Here are a few bits of extra data that are useful to add to a point
>> (1) provenance
>> (2) datum (I try to stick to WGS84,  but points from freebase occasionally
>> have a Datum attached,  so I store it)
>> (3) circular error (the accuracy of the determination of the point,  for
>> instance the technical limitation of a GPS receiver)
>> (4) scale length of feature (how accurate do we have to be?  it's not
>> worth getting into an edit war over the exact point that represents,  say,
>> Finland.)
>> (5) an overall quality rating (so if we've got ten points we can pick the
>> best)
>>     Note that (3) and (4) are weakly exclusive of each other.  If,  for
>> instance,  I'm representing a GPS point that the camera was at when a photo
>> was taken,  that's literally just a point,  and (4) is zero.  On the other
>> hand,  (4) >> (3) if the point represents "New York City",  because you
>> can't really fix the location of something that sized to more than a few km.
>>     This distinction is really important in doing data cleaning work.  If
>> several sources disagree about the location of NYC by a few km,  it's best
>> to let them "agree to disagree" -- either pick the one you like the best
>> (Wikipedia centers NYC at the intersection north of the Port Authority and
>> the NY Times building,  sweet...) or you take the centroid of them.  No
>> matter what you do,  you want to use a cheap heuristic and not spend
>> expensive resources on this non-problem.
>>     On the other hand,  if coordinates for the "Statue of Liberty" were
>> off by a km from different sources,   that indicates that a real problem,
>> and some action ought to be taken.
> --
> ----------------------------------------------------------------
> 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
> ------------------------------------------------------------

Sean Gillies
Institute for the Study of the Ancient World
New York University
Received on Monday, 11 October 2010 17:31:28 UTC

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