Subject: Re: [Geojson] Making GeoJSON explicitly cartesian

From: Matthias Müller <[email-masked]>
Date: Wed, 16 Mar 2016 10:15:00 +0100

Sorry for the late comment, I just became aware of the discussion on
Cartesian coordinates.

WGS84 and Cartesian interpolation are two things that do not go together
well. Cartesian interpolation makes sense for engineering CRSes but not for
real world coordinates (Simon Cox' / John Herring's mail  - Is GML
Cartesian? - has pointed this out). I do see a reason to support this legacy
burden (WGS84+cartesian) in GeoJSON because people have gotten used to it.
But there is also an increasing number of libraries (D3 was mentioned,
Lucene/Elasticsearch and spatial4j  are further examples) that handle
Geographic (great circle) distances very well and justify demand for a
standardized encoding.
I haven't yet spotted any simple (this excludes GML), standardized encoding
formats for geographic geometries, and since GeoJSON is currently under
revision for IETF it could fill this gap.

Did this group consider the opportunity of two additional Geometry types for
Geographic interpolation, e.g. GeodesicLineString and GeodesicPolygon:

## GeodesicLineString
{ "type": "GeodesicLineString",
    "coordinates": [ [100.0, 0.0], [101.0, 1.0] ]
    }

and
##GeodesicPolygon
"geometry": {
           "type": "GeodesicPolygon",
           "coordinates": [
             [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0],
               [100.0, 1.0], [100.0, 0.0] ]
             ]
         }

Cheers,
Matthias

---

From: Martin Daly <[email-masked]>
Date: Wed, 16 Mar 2016 09:57:10 +0000

Matthias,

> Geographic interpolation, e.g. GeodesicLineString and GeodesicPolygon:

I don't see much chance of this significant change being included at such a late stage. Plus, adding them to core GeoJSON would be a burden on all implementations.

Instead, I suggest that you specify the Geodesic[LineString|Polygon] variants in a similar-but-different JSON encoding that can share all of the foundations of GeoJSON, but is not GeoJSON.

GeodesicJSON would seem like a good name...

Martin

---

From: Erik Wilde <[email-masked]>
Date: Wed, 16 Mar 2016 10:21:32 +0000

hello matthias.

thanks for your feedback!

> Geographic interpolation, e.g. GeodesicLineString and GeodesicPolygon:

as pointed out already, that is unlikely to happen this late in the 
game. and just to point this out before a discussion starts around 
adding these new geometry types as an extension: one goal of the new 
draft was to be more explicit about its extension model, and thanks to 
this effort, we now have the following text:

https://tools.ietf.org/html/draft-ietf-geojson-01#section-6.2

"Implementations MUST NOT extend the fixed set of GeoJSON types: 
FeatureCollection, Feature, Point, LineString, MultiPoint, Polygon, 
MultiLineString, MultiPolygon, and GeometryCollection."

this means that even though your motivation to have the geodesic 
features mentioned above is understandable, you are not able to just add 
them to the set of geometry types in geojson.

thanks and cheers,

dret.

-- 
erik wilde | mailto:[email-masked] |
            | http://dret.net/netdret    |
            | http://twitter.com/dret    |

---

From: Matthias Müller <[email-masked]>
Date: Wed, 16 Mar 2016 11:46:18 +0100

Martin,

I suggested GeodesicString because it is consistent with ISO19107, which is the successor of [OGC 99-049] -- the conceptual foundation of GeoJSON. This spatial schema has evolved a lot since 1999 and I was hoping that GeoJSON could catch up a bit regarding real-world representations. In the past, people often used cartesian interpolation on WGS84 as a workaround since geodesic interpolation for real-world geometries was expensive to compute on 1990ies hardware. Nowadays, that argument is largely obsolete but I still see that technology and conceptual models are heavily affected by this old workaround.

Nevertheless, if my comments are too late now, I'll stop talking here.

Matthias

-----Original Message-----
From: GeoJSON [mailto:[email-masked]] On Behalf Of Martin Daly
Sent: Wednesday, March 16, 2016 10:57 AM
To: 'Matthias Müller'; [email-masked]
Subject: Re: [Geojson] Making GeoJSON explicitly cartesian

Matthias,

> Did this group consider the opportunity of two additional Geometry 
> types for Geographic interpolation, e.g. GeodesicLineString and GeodesicPolygon:

Martin

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