New property crs

[open-north]

Geographic coordinates can be specified using different coordinate reference systems (CRS). WGS84 is a common one.

A CRS can be valid for a whole file or only for single columns. This is the case if coordinates are specified in several CRS in a single file.

A simple possibility is to specify the CRS as a property crs of a column. This covers both cases. Here is an example:

{
  "name" : "geogrLongitude",
  "type" : "number",
  "description": "location of the station (longitude)",
  "crs": "EPSG:4326"
}

[nichtich]

This is a rather specific use case. It should be supported to encode CRS information but not as part of the schema specification. How about:

{
  "name" : "geogrLongitude",
  "type" : "number",
  "description": "location of the station (longitude) in EPSG:4326 system"
}

[jze]

It's not that uncommon. It is estimated that 80% of all data is geo-related. And coordinates in WGS84 are the exception rather than the rule - even if everyone knows them.

To make the data machine-readable, the information on the CRS must be machine-readable and therefore part of the schema.

[nichtich]

Ok, GeoJSON is fixed on WGS 84 so to express other coordinate systems it needs to be documented somehow.

First of all "crs" need to be defined more clearly. Does it also cover coordinate systems of extraterrestial bodies? Which codes are allowed? Best I could find is https://spatialreference.org/, so for instance IAU2000:30100 references Moon 2000 CRS, ok?.

Second, which base type shall be restricted by the new property? It sure makes sense for geopoint but plain number can have a vast number of context and we don't want to put all kinds of contexts in the specification. Maybe this can be solved together with #352 and related data type issues.