[Geojson] Problem in Twitter's GeoJSON

[Tim Schaub]

Tim Schaub wrote:
> Hey-
> 
> David William Bitner wrote:
>> GeoJson is set up to deal with data in both Latitude Longitude where 
>> the standard is typically Lat then Lon and with projected coordinate 
>> systems where the standard is typically x then y.  GeoRSS is set up to 
>> by default only deal with data in Geographic Coordinates and it is 
>> only in the "more cumbersome" representations that projected 
>> coordinate systems are used along with SRIDs.
>>
> 
> Right.  It would be silly to say a format *always* specifies coordinates 
> in northing, easting order because this typically maps to axes referred 
> to as y, x in projected space - and the alphabet (and other conventions) 
> specify x, y order.
> 
> Where a format allows for more than one coordinate reference system, the 
> format specification can require that all clients carry around a table 
> of all possible reference systems that they might expect to encounter - 
> and they can leave it up to the definition of the coordinate reference 
> system to say what the order of the coordinates means in terms of 
> direction.  This is what GML and others do.
> 
> This is cumbersome (for every client to carry around a table of every 
> possible CRS).
> 
> Instead, if you say the first coordinate is always "x" and the second 
> coordinate is always "y" things will be mapped correctly by most people 
> in most cases (as the common convention is that "x" means vertical and 
> "y" means horizontal and people typically think of north as up).
> 

and of course that is "x" means horizontal and "y" means vertical.

/me slaps self

> http://geojson.org/geojson-spec.html#positions
> 
> Tim
> 
> 
>> On Tue, Nov 24, 2009 at 11:30 AM, Raffi Krikorian <raffi at twitter.com 
>> <mailto:raffi at twitter.com>> wrote:
>>
>>>     Twitter has crossed up easting and northing in their API docs, 
>>> and I      see it in their API responses too. Can anybody following 
>>> this list get      the word to those developers?
>>>
>>>     --
>>>     Sean Gillies
>>>     Programmer
>>>     Institute for the Study of the Ancient World
>>>     New York University
>>     hmm. it does seem like we have it reversed -- we're sending northing
>>     then easting in our coordinates.  thanks for letting us know!
>>
>>     just out of curiosity, why is this represented as so, when GeoRSS
>>     has a point defined as a latitude-longitude
>>     pair? http://www.georss.org/simple#Point.
>>
>>     --
>>     Raffi Krikorian
>>     Twitter Platform Team
>>     raffi at twitter.com <mailto:raffi at twitter.com> | @raffi
>>
>>
>>
>>
>>
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>>
>>
>>
>>
>> -- 
>> ************************************
>> David William Bitner
>>
>>
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>>
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> 
> 


-- 
Tim Schaub
OpenGeo - http://opengeo.org
Expert service straight from the developers.