[Geojson] Problem in Twitter's GeoJSON

[Tim Schaub]

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).

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