[GeoJSON] spec clarification of CRS

[Raj Singh]

On Dec 11, at 3:42 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
> 

Correct me if I'm wrong, but I'm still feeling contradiction within the spec:

1) Section 2.1.1 says to me that any "positions" in a GeoJSON file will "follow x, y, z order". If that is true, then...
2) Section 3.1 says "urn:ogc:def:crs:OGC:1.3:CRS84 shall be preferred over legacy identifiers such as EPSG:4326". That says to me that EPSG:4326 is not preferred, but allowed. However, EPSG:4326 doesn't follow x, y, z order. So doesn't that make it illegal to use in GeoJSON?

I'm not trying to open or re-open any discussion on CRS support. I just want to know if GeoJSON only supports CRSes that follow x, y, z order. If so, then section 3.1 is ambiguous. If not, then section 2.1.1 is misleading.

---
Raj