Schema: validation of image-coordinate-reference-system

In the current iFDO schema, the value of the image-coordinate-reference-system is not matched to a pattern for validation.

Version 2.1:

"image-coordinate-reference-system": {
     "description": "The coordinate reference system, e.g. EPSG:4326",
     "type": "string"
}

To avoid user inputs like "WGS 84", it is suggested to be more precious in the description and match the string to a pattern.

Suggestion:

"image-coordinate-reference-system": {
     "description": "The identifier of the coordinate reference system, which contains the authority name and code, e.g. EPSG:4326",
     "pattern": "^(?:EPSG|ESRI|IAU_2015|IGNF|NKG|OGC):.+$"
     "type": "string"
}

Note:

• WGS84 is not ambigous and could mean EPSG:4978, EPSG:4979, EPSG:4326
• CRS overview