On Tue, Jan 11, 2011 at 1:30 AM, Gabriel Roldán <[email protected]> wrote:
> chiming in late due to vacations.
>
> The idea is sound and needed. I'm wondering if there's any conceptual
> difference between your EPSG:0 CRS and the CRS:1 special CRS defined in
> the WMS 1.3 spec (see section 6.7.2 and 6.7.3.5). If there's not we
> should use CRS:1, but I think there is a difference in that CRS:1
> forcedly has a 0,0 coordinate origin and yours is tied to the layer
> bounds as declared by the datastore?
>
> In any case, CRS:1 seems worth to support at some point.
>
> excerpt:
> "6.7.3.5 Geographic information with undefined CRS
> A server
> may offer two-dimensional geographic information whose precise spatial
> reference is undefined. For example, a hand-drawn historical map may
> represent an area of the Earth but not employ a modern coordinate
> reference system, and an aerial photograph may not be precisely
> georeferenced. Such types of graphical information shall be treated as
> an image, and the Map CS label “CRS:1” shall be used when declaring the
> Layer CRS of such an object. Clients should not attempt to overlay a
> layer for which CRS=CRS:1 with another layer."

Ah ha, nice to know about this one.
Might be a good fit, there are a few things to double check before
going down this road:
- in our code there is a widespread assumption that all codes are in the EPSG
  authority, consider for the example the axis flipping code in WFS
- EPSG:0 would also be usable as urn:ogc:, the same cannot be said about CRS:1
- what is the behavior of CRS:1 regards to reprojection? EPSG:0 would not
  throw exception in case of reprojection, would just never change the
coordinate
  values

In any case, the major concern about CRS:1 is its usability in WFS/WCS, I did
not check in detail but the gut feeling is that it might require
extensive changes to
be used there.

Cheers
Andrea

-- 
Ing. Andrea Aime
Technical Lead

GeoSolutions S.A.S.
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