[Geojson] Interpretation of "extra" coordinate dimensions

[Daniel Azuma]

Hi everyone,

Just joined the list, so a quick intro: My name is Daniel Azuma. I wrote and maintain a GeoJSON builder/parser for Ruby called rgeo-geojson. (http://virtuoso.rubyforge.org/rgeo-geojson/) It parses GeoJSON into objects built by RGeo, which is a Ruby implementation of the OGC SF spec.

Right now my parser ignores and throws away any "extra" dimensions beyond XYZ(M), because the SF spec (and hence RGeo) doesn't have any notion of dimensions beyond XYZM. However, I notice that the GeoJSON spec does allow for any number of dimensions in a coordinate. I wanted to ask what is generally expected of parsers when dealing with such "extra" dimensions, whether they should be considered meaningful.

I ask because I have a user who wants to use extra dimensions to store metadata associated with point coordinates. That is, he wants to do this:

{
    "type": "Point",
    "coordinates": [102.0, 0.0, 0.0, "2011-03-29T08:38:50Z", 3.54, 39.80]
}

where the coordinates are X, Y, Z, timestamp, speed, bearing. I responded to him that I thought such metadata should be represented as properties in a Feature object, but he prefers conciseness over expressiveness in his use case. So I was wondering about the intent of allowing arbitrary extra dimensions in a coordinate, and whether, in the opinion of the authors of the spec, this was a case that GeoJSON parsers do (or should) handle.

Thanks!
Daniel Azuma