On 03/03/14 15:50, addshorewiki wrote:
This should probably be directed at
https://github.com/Wikidata/Wikidata-Toolkit/issues ?
Yes, details related to the ongoing development of Wikidata Toolkit
should be discussed elsewhere. In this particular case, part of the
problem can probably be solved by having a look at the documentation of
the code [1].
Anyway, part of the question is also about the Wikibase data model for
globe coordinates and the related JSON. I can say something about this:
* GlobeCoordinates store numbers for latitude, longitude, and precision.
* The "precision" value is restricted: only a small number of values are
allowed (the ones that one can enter through the UI). This probably
needs more documentation [2].
* The accuracy of coordinates is inherently limited (you cannot
meaningfully define locations beyond a certain precision). This is in
contrast to the Quantity type where we have arbitrary precision decimals.
* The exact format of the numbers is not completely fixed yet. The
current proposal is to measure all values in degrees with a guaranteed
accuracy of 9 digits (that means: "up to nanodegrees"). This should be
enough for all practical purposes. (Note that I am talking about the
accuracy of the decimal numbers here, not about the GlobeCoordinates'
"precision" value, which is also a number of the same accuracy.)
* Most programming languages do not have a "9 digit fixed precision
decimal" datatype that could exactly capture this. To represent such a
number you can store integer values that give the amount in nanodegrees
(the degree value multiplied by 10^9); overflows are unlikely in 64bit
integers since latitude and longitude cannot be very large numbers. With
9 decimal digits, one could also use double without significant errors.
These two views can easily be converted back and forth.
* The current JSON (internal and external) gives the numbers as
serialisations of floating point values (in rare cases even using e
notation). In the future, these should be decimal values (can still be
read as floats but won't use e notation).
A definite clarification of this issue will be provided soon, but the
above is the current status.
Markus
[1]
https://github.com/Wikidata/Wikidata-Toolkit/blob/master/wdtk-datamodel/src/main/java/org/wikidata/wdtk/datamodel/interfaces/GlobeCoordinatesValue.java
[2] https://bugzilla.wikimedia.org/show_bug.cgi?id=62105
Addshore
On 3 March 2014 15:45, Fredo Erxleben <fredo.erxle...@tu-dresden.de
<mailto:fredo.erxle...@tu-dresden.de>> wrote:
Hey there,
While testing I found that the notations of precision in the
internal dumpfiles is not always what I expected:
My example is the item Zwickau (json and stacktrace attached):
The precision in the geolocation is denoted as an decimal value,
while the implementation of GlobalCoordinatesValueImpl requires a
long value encoding a precision.
How should this discrepancy be handled best?
Greetings,
Fredo
PS: I am at the moment checking all the errors that occur while
converting an earlier dumpfile, so I am likely to stumble upon more
problems soon.
_______________________________________________
Wikidata-tech mailing list
Wikidata-tech@lists.wikimedia.org
<mailto:Wikidata-tech@lists.wikimedia.org>
https://lists.wikimedia.org/mailman/listinfo/wikidata-tech
_______________________________________________
Wikidata-tech mailing list
Wikidata-tech@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikidata-tech
_______________________________________________
Wikidata-tech mailing list
Wikidata-tech@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikidata-tech
