[GeoJSON] Removing CRS from GeoJSON

Thu May 16 12:10:58 PDT 2013

I agree with deprecating CRS with no replacement.

Maybe if people want other coordinate systems, they can reuse the GeoJSON syntax but embed it into some kind of CRS wrapper. That lets people reuse GeoJSON parsing code but the wrapper should not be called GeoJSON. (Not sure if I'm making sense here…)

Allan

On May 16, 2013, at 2:58 PM, Tim Schaub <tschaub at opengeo.org<mailto:tschaub at opengeo.org>>
 wrote:

I like the proposal Sean.  Curious exactly what you mean by deprecate (remove "crs" with no text mentioning it, or say "crs" is deprecated and describe what it used to be like?).

Regarding GeoServer, it is a good question.  I haven't discussed this with others in that community, but I'd say GeoJSON would become more like KML - GeoServer can serialize feature collections as both, but you can't request data in arbitrary reference systems.

It's also my opinion that clients can use other formats if they need functionality not covered by GeoJSON (we don't handle complex features particularly well, for example).  A capable web client can consume GML from GeoServer's WFS if it wants data in an arbitrary crs or needs complex features.  In addition, I don't personally feel like GeoJSON + WFS is a natural mix (WFS-T for example, doesn't work).

Tim

On Thu, May 16, 2013 at 12:26 PM, Sean Gillies <sean.gillies at gmail.com<mailto:sean.gillies at gmail.com>> wrote:
All,

How about this for a plan: submit an I-D that deprecates the old crs object, omits the new proposed crsURN object, and doesn't otherwise change the geojson.org<http://geojson.org/> spec. After it is submitted, we reexamine the CRS situation in light of comments we'll (hopefully) get. My hypothesis is that this compatibility-breaking change doesn't actually break very much in practice.

As a consequence there will be what looks to a lot of GIS folks like a gap in the spec. We'll need to be able to live with the multiple gap-filling measures they'll come up with. For example, Tim, what's GeoServer going to do to satisfy WFS requests for GeoJSON in EPSG:27700 (or urn:ogc:def:epsg::27700)?

On Wed, May 15, 2013 at 11:08 AM, Tim Schaub <tschaub at opengeo.org<mailto:tschaub at opengeo.org>> wrote:
Tim, I think the situation that we have at the moment is better than you describe, but not by much. We have “allow any CRS and axis order will always be lon/lat or easting/northing”. We did that to avoid the burden of carrying around axis order knowledge. But it still has the burden on needing to know what EPSG:27700, or whatever, means. Web clients still have to get the WKT, Proj.4 string, etc, from that id (assuming that they can work with the result). So we dodged one bullet, but not the other, arguably more complex, one.

Regarding the bullet dodging, web clients don't actually have to know squat about EPSG:27700 if they use GeoJSON and WMS 1.1 - they just have to match strings to know that they are the same.  WMS 1.1 described a rendering service where coordinate order could be mapped to rendering concepts like "top" and "left" (well known by web clients who deal with images).  GeoJSON maintained the same - a known mapping of coordinate order to rendering orientation.  So we very intentionally made GeoJSON work well with existing rendering services.

Here’s a pull request of mine:

https://github.com/GeoJSONWG/draft-geojson/pull/3

Martin

From: geojson-bounces at lists.geojson.org<mailto:geojson-bounces at lists.geojson.org> [mailto:geojson-bounces at lists.geojson.org<mailto:geojson-bounces at lists.geojson.org>] On Behalf Of Tim Schaub
Sent: 15 May 2013 05:41
To: geojson at lists.geojson.org<mailto:geojson at lists.geojson.org>
Subject: [GeoJSON] Removing CRS from GeoJSON

So as to avoid hijacking Sean's thread, I'll start a new one here.

I'm in favor of restricting the allowed coordinate reference systems for GeoJSON objects to 1: latitude, longitude coordinates relative to an ellispoidal CRS based on the WGS84 datum.

I think the second best alternative would be to restrict to 2 CRS: CRS84 or EPGS:3857.

I don't like the "allow any CRS and let axis order follow the CRS" because I think it either reduces interoperability or imposes an unreasonable burden on web clients (I don't know of a good web service - or really want to depend on one - that provides axis order information for arbitrary CRS URN, and the table is too big to ask every client to carry around).

I apologize for having missed earlier "discussion" [1]. I haven't dug down to that epoch in my inbox yet.

And I'm in favor of the proposed RFC to IETF [2].

https://github.com/GeoJSONWG/draft-geojson/pull/2

[1] http://lists.geojson.org/pipermail/geojson-geojson.org/2013-April/000712.html
[2] http://lists.geojson.org/pipermail/geojson-geojson.org/2013-April/000713.html

Tim

PS - Do the build artifacts (xml, txt, etc) need to be in the repo? If so, can someone update the README.md with detail on building them?

PPS - Mildly curious what it means to be "commented out" as an author. I do see a comment that suggests authors should be asked if they are willing to be authors. Happy to entertain that question.

--
Tim Schaub
OpenGeo http://opengeo.org/
Expert service straight from the developers.

--
Tim Schaub
OpenGeo http://opengeo.org/
Expert service straight from the developers.

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Sean Gillies

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Tim Schaub
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