[Geojson] coordinate order
Norman Vine
nhv at cape.com
Mon Mar 10 12:55:58 PDT 2008
Tim Schaub writes:
> Sean Gillies wrote:
> > Tim Schaub wrote:
> >>
> >>
> >> 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]
> >> }
> >> }
> >>
> >
I thought we meant that if the coordinate order was different then X,Y
then even if crs was present that one must supply "coordinate_order"
So proper access to the coordinate array coords[] for 'simple clients'
could still be done eg.
for point in coords:
x = point[coordinate_order[1]]
y = point[coordinate_order[0]]
Note that for clients that know the CRS this might simplify to
for point in coords:
lat = point[0]
lon = point[1]
As this is implied by the CRS
Cheers
Norman
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