2013/1/8 Gregor Hagedorn <[email protected]> > ON COORDINATES: > > a) what you describe is more specific than a geolocation (which may be > expressed by other means than coordinates). I suggest to give the data > type the more specific name: > > geocoordinates >
Yep, agreed. Or just coordinates. > > b) with respect to precision: I don't understand the reasoning to > stick this to degrees. Since we are describing locations on an > ellipsoid, the longitude to distance and latitude to distance > conversions are different, and they are different for different points > on earth. See example on en.wikipedia, a minute at equator is 1843 > versus 1855 m. > The model defines it as using the arcdistance on the given equator. > > In practice the potential location error will be given in a distance > measure. You want to convert it to degrees in a highly complex > conversion. Why? The back conversion will usually be non-ambiguous > (since the backconversion will always describe an ellipsis rather than > a circle). > > In practice the value will be given as 44°15'. Then we know it is by the minute - and not that it is given by a nautical mile. I am not making a highly complex conversion -- I am just looking at the number and saying "oh yeah, this seems to be given by the minute, and not by the second or by the degree". The reason why I prefer degrees on a given equator to meters is that it makes more sense on varying globes, like the Earth, Moon, Sun, Jupiter, and Phobos. What we need is the possibility to understand that 44°15' should not be displayed as 44°15'00.001" the next time the value is displayed. And by saying it is correct by the minute allows us to do so. Making the statement in meters would actually require us to make that complex calculation which would be based on the given geodetic system -- which is much more complicated than the current suggestion. > c) Furthermore, as before, I believe that precision and accuracy will > usually both contribute to the error your are interested in and which > is typically described in geolocations having a +/- addition. > > I suggest to replace precision with > errorradius > or > uncertaintyradius > or > uncertaintyInMeters > > which would be the great circle distance. To somewhat simplify, the > unit could be fixed to m. > I think precision is actually what I mean here for geocoordinates: with how much precision is the coordinate given? How many 0s after the dot need to be written? Is the minute specified or not? Is the second specified? This can be used for transforming from one geodesic system to the other, or, simpler, from degree minute seconds to degree in decimals. But then again, I don't mind calling it uncertainty or uncertaintyRadius. > > Here is some work done in our area (biodiversity): > http://code.google.com/p/darwincore/wiki/Location > > The term there is > http://terms.gbif.org/wiki/dwc:coordinateUncertaintyInMeters > > Yep, pretty much what I meant, just that I am suggesting not to use meters but something that is easier to translate into degrees. > d) the correct name for "globe" is "Geodetic datum" or "geodetic > system" (which is more than the globe). See > http://en.wikipedia.org/wiki/Geodetic_system or > http://terms.gbif.org/wiki/dwc:geodeticDatum. WGS 84 (as a wikidata > item) is a valid geodetic datum or system. Both terms are equally > correct. "Globe" is not correct. > > OK. > Gregor > > _______________________________________________ > Wikidata-l mailing list > [email protected] > https://lists.wikimedia.org/mailman/listinfo/wikidata-l > -- Project director Wikidata Wikimedia Deutschland e.V. | Obentrautstr. 72 | 10963 Berlin Tel. +49-30-219 158 26-0 | http://wikimedia.de Wikimedia Deutschland - Gesellschaft zur Förderung Freien Wissens e.V. Eingetragen im Vereinsregister des Amtsgerichts Berlin-Charlottenburg unter der Nummer 23855 B. Als gemeinnützig anerkannt durch das Finanzamt für Körperschaften I Berlin, Steuernummer 27/681/51985.
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