[Geowanking] Re: Specifying units of the RDF geo:alt property
kjetil at kjernsmo.net
Tue Nov 22 13:35:03 PST 2005
Hello again, everyone!
It has taken me so long to get my things together. My old harddrive and
my PSU died, and I moved out of my appartment, but now, I'm back! :-)
So, I had a long chat today in real life with the big, bearded guy who
> Hi Kjetil,
> On Tue, 01 Nov 2005 23:54:44 +0100, Kjetil Kjernsmo
> <kjetil at kjernsmo.net>
> > Currently, it is undefined what it is...
> > In a recent chat on #swig on irc.freenode.net, Dan Brickley
> > suggested I should take the issue to these list, and he would
> > implement any consensus that is formed here.
> > I would personally tend to favour that the geo:alt property is
> > specified as "The altitude above the local WGS 84 ellipsoid in
> > meters", but clearly, this is problematic if there is allready a
> > lot of data in the wild where it is given in e.g. feet. Then, I
> > guess, the only hope is to use rdf:value, as seen in the example
> I'd like to see people using datatypes to do this. In the SWAD-E
> geoInfo workshop in Budapest we came up with a couple of simple
> approaches to describing what floor of a building you are on  -
> something that is available to many people who don't have a GPS and
> rely on looking up their wgs84 points on some map. (I have no idea
> what the altitude of my office is in any unit except floors).
The obvious concern that I cited was that much of the existing data
would never change, and so would be useless unless we define something
for the case of no given datatype. Chaals elaborated on this in our
real-life chat today: He suggested that we label the properties as
such: "geo:alt is in units of meter above the local ellipsoid unless a
different datatype is given". Which I find a workable and practical
solution. When people start using data types, the reliability of the
data will increase, but the allready available data will not be
This approach should also be OK for Frank's aircraft fuel capacity use
case, I suppose.
For consistency, we should probably define the "default" unit of lat and
long to decimal degrees as well.
IIRC, DanC mentioned on #swig that an elaborate effort on units was just
getting started. That's of course very interesting, but I think we
should move forward with this rather fast, it doesn't serve us well
when it is underspecified, like now.
More information about the Geowanking