[Geojson] Valid values for numbers in points etc?

Francis Galiegue fgaliegue at gmail.com
Thu Mar 7 12:14:46 PST 2013

On Wed, Mar 6, 2013 at 6:03 PM, Michael Geary <mg at mg.to> wrote:
> The meaning of the coordinate values depends on the coordinate reference
> system (CRS) the GeoJSON file uses.
> The default CRS is WGS84 (EPSG:4326), where the values do represent
> longitude, latitude, and optional altitude.
> If you specify a different CRS in the GeoJSON file, then the coordinate
> values are easting, northing, and again optional altitude. The meaning of
> the easting and northing depends on the CRS. I believe altitude is in meters
> in all cases; someone correct me if I'm wrong.
> As an example, my PolyGonzo library accepts GeoJSON in either the default
> WGS84, or alternatively in Spherical Mercator (EPSG:3857) coordinates, also
> known as Google Mercator. These are coordinates in "meters" on the projected
> Spherical Mercator plane. If you use this in the GeoJSON, it allows slightly
> faster display of the polygons because it only takes a single multiplication
> to convert each coordinate to a pixel location instead of a sequence of
> trigonometric operations.

Hmm, so the schemas I have written should be really split in two. I
guess there is no defined way to tell from the get go if one GeoJSON
representation is written using one coordinate reference system or
another? How do APIs know whether one or the other coordinate system
is used?

Francis Galiegue, fgaliegue at gmail.com
JSON Schema in Java: http://json-schema-validator.herokuapp.com

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