[Geojson] coordinate order

[Martin Daly]

For completeness should we also add:

"coordinate_direction": [1,-1]

or similar? That would allow south, west and down positive ordinates.  
Some country-specific (mostly projected) CRS-s are like this.

However, I also agree that it is ready to go out into the wild.

M

On 7 Mar 2008, at 18:34, Tim Schaub wrote:

> Hey-
>
> See the updated GeoJSON spec v5
> http://wiki.geojson.org/GeoJSON_draft_version_5
>
> We had a discussion on IRC today about geometry coordinates.  We all
> agree that we want to support more than two dimensions.  We also want
> simple clients to be able to know which dimensions at least the first
> two elements in a coordinates array refer to.
>
> Regarding more than two dimensions, the spec talks about two  
> dimensions
> for point geometry and goes on to say "any number of additional
> dimensions are allowed, and interpretation and meaning of these
> coordinates is beyond the scope of this specification."
>
> Does this sit well?  We say you've got to have two elements in the
> coordinates array but more are allowed.
>
> Regarding the order of elements in the coordinates array for GeoJSON
> geometries, we say that the first two elements are in x, y order (lon,
> lat for dd).  This is what we have said from the start.
>
> The change to the spec is to accommodate CRS that define a different
> coordinate order.  Instead of requiring all clients to know about all
> CRS coordinate order conventions, we require that GeoJSON geometries
> referencing a CRS that defines non-xy coordinate order include a
> "coordinate_order" member in the CRS object.
>
> This means a point geometry that references EPSG:4326 would look  
> like this:
>
> {
>    "type": "Point",
>    "coordinates": [-180.0, 90.0],
>    "crs": {
>        "type": "EPSG",
>        "properties": {"code": 4326},
>        "coordinate_order": [1, 0]
>    }
> }
>
> The benefits of this are that it allows all clients simple access to  
> the
> proper dimensions in the geometry coordinates array and allows smarter
> clients who are strict about CRS coordinate order to map to the  
> correct
> dimension in our coordinates arrays.
>
> The drawbacks of this are that people like to argue that the EPSG has
> the right to assign meaning to any sequence of numbers in a data
> structure that references EPSG.  I say that is fine, they get access  
> to
> our coordinate_order array.  If the EPSG says that the first value  
> in a
> sequence refers to the northing of a point, then they look at the  
> first
> value in our coordinate_order array and know which element to use from
> our coordinates array.
>
> Makes things a bit more complex for clients who know about CRS and
> simpler for the rest.
>
> I think this thing is ready to let out into the wild.
> Tim
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