On Jan 11, 2015 6:59 AM, "Markus Krötzsch" <markus@semantic-mediawiki.org> wrote:

On 11.01.2015 14:53, Maarten Dammers wrote:

Hi Markus,

Markus Krötzsch schreef op 11-1-2015 om 2:15:

Hi,

Does anybody know the current documentation of the precision of the
globe coordinate datatype? This precision was introduced after the
original datamodel discussions.

No clue, I do know we have to do some conversions. See
https://git.wikimedia.org/blob/pywikibot%2Fcore.git/HEAD/pywikibot%2F__init__.py#L290
for the relevant Pywikibot code.

Aha, so Pywikibot converts from "approximate size of the object" to "approximate precision of the coordinates" (the latter must take into account how far north the point is). Are you saying that the seemingly odd precision values in Wikidata have been created in an attempt to draw a tight bounding box around an object of a given approximate size? Do you think this encoding of approximate size is a good way of handling this information?

Do the reverse on seemingly odd values
and you probably end up with a nice dimension. Dimension is documented
at https://www.mediawiki.org/wiki/Extension:GeoData#Glossary

Yes, this operation could surely be reversed without loss of precision if one knows the "radius" of any body on which we have coordinates. However, I am not sure if this "size of the object"-interpretation of precision is what Wikidata wants to say here in the first place. At least in the UI it looks more like a kind of "precision of measurement" or (worst case) some mixture of both.

For Wikidata Toolkit, the big question is whether we should continue to try and convert the data to something that matches what the UI supports, or whether we should give up and say "precision is just any number -- make of it what you want".

Markus

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