[GeoJSON] spec clarification of CRS

[Tim Schaub]

Hey Raj,

The key part for me is that the spec must work for clients "without
the ability to dereference any CRS definition" (as Martin put it).
Any web client already deals with "top" and "left" rendering concepts.
 Having a feature format that provides coordinate values that can be
"mapped" to these orientations is useful.  Having a format that
requires a separate lookup to know what the values mean imposes an
unnecessary burden (even if you could point me to the service that
provides axis order for arbitrary CRS identifiers).

WMTS is tragically comical in this regard.  Its <TopLeftCorner>
element contains two values, but clients can't determine which one is
"top" and which one is "left."

Tim



On Wed, Dec 11, 2013 at 1:42 PM, Martin Daly <Martin.Daly at cadcorp.com> wrote:
>> I'd like to suggest that in section 3.1 Named CRS [1], a sentence be added
>> that says, "EPSG:4326 identifiers such as EPSG:4326 and
>> urn:ogc:def:crs:EPSG:6.6:4326 are prohibited, as they define coordinate
>> reference systems with Y-X axis order, which is illegal according to section
>> 2.1.1."
>> (a good reference on the issue is [2]).
>
> -1
>
>> As we move into 2014, confusion still reigns on this issue. And the current
>> wording of the GeoJSON spec implies that EPSG:4326 is OK, which is an
>> internally contradictory statement. Don't make the same mistake OGC did a
>> decade ago!
>
> I, for one, completely disagree. GeoJSON is explicit and consistent about axis order of the coordinates. All that it says is " use any CRS you like, but *always transfer the coordinates in this pre-defined order*".
>
> That way, clients can be 100% sure that they can take the coordinates on face value, with or without a priori knowledge of the CRS, and with or without the ability to dereference any CRS definition.
>
> No mistakes, no confusion. At least on the part of GeoJSON.
>
> Martin
>
> _______________________________________________
> GeoJSON mailing list
> GeoJSON at lists.geojson.org
> http://lists.geojson.org/listinfo.cgi/geojson-geojson.org



-- 
Tim Schaub
Vice President, Engineering | Boundless
tschaub at boundlessgeo.com
@tschaub