Allow epsg-code to be provided as string?

[m-mohr]

The specification asks to provide EPSG codes as numbers (e.g. 4326 instead of EPSG:4326). We see many code snippets that actually use the string variant, which strictly speaking should be WKT2.

So an idea coming up in recent discussions is that we use the clients to correct this common mistake.
So for subtype epsg-code a client could simply match against the pattern/regexp /^EPSG:(\d{4,})$/i and replace it with the first match converted to an int.

In pseudo-code something like:

if $subtype == 'epsg-code':
  $matches = $value.match(/^EPSG:(\d{4,})$/i)
  if $matches:
    $value = int($matches[1])

[clausmichele]

The Equi7 requires the following string to be parsed for using it in load_collection
https://discuss.eodc.eu/t/get-specific-data-extent-using-equi7-coordinates/223
"crs": "PROJCRS[\"Azimuthal_Equidistant\",BASEGEOGCRS[\"WGS 84\",DATUM[\"World Geodetic System 1984\",ELLIPSOID[\"WGS 84\",6378137,298.257223563,LENGTHUNIT[\"metre\",1]]],PRIMEM[\"Greenwich\",0,ANGLEUNIT[\"degree\",0.0174532925199433]],ID[\"EPSG\",4326]],CONVERSION[\"Modified Azimuthal Equidistant\",METHOD[\"Modified Azimuthal Equidistant\",ID[\"EPSG\",9832]],PARAMETER[\"Latitude of natural origin\",53,ANGLEUNIT[\"degree\",0.0174532925199433],ID[\"EPSG\",8801]],PARAMETER[\"Longitude of natural origin\",24,ANGLEUNIT[\"degree\",0.0174532925199433],ID[\"EPSG\",8802]],PARAMETER[\"False easting\",5837287.81977,LENGTHUNIT[\"metre\",1],ID[\"EPSG\",8806]],PARAMETER[\"False northing\",2121415.69617,LENGTHUNIT[\"metre\",1],ID[\"EPSG\",8807]]],CS[Cartesian,2],AXIS[\"easting\",east,ORDER[1],LENGTHUNIT[\"metre\",1,ID[\"EPSG\",9001]]],AXIS[\"northing\",north,ORDER[2],LENGTHUNIT[\"metre\",1,ID[\"EPSG\",9001]]]]"

[m-mohr]

Is that a client or a server issue, @clausmichele ?

[clausmichele]

Well, the question is: how does the client understand if the provided value is an integer referring to a crs code, an epsg code string or a WKT string?

[m-mohr]

Does the client need to understand it? Usually, it just needs to be passed through to the server, no?

[clausmichele]

Yes, but from this issue https://github.com/openEOPlatform/architecture-docs/issues/159#issuecomment-978126164 it seemed that the plan was to convert an EPSG string to the integer representing it client side, since the API requires a crs to be specified as an integer.

[m-mohr]

Oh, I see... well you can easily distinguish them, see the pseudo-code below for an example:

if (val is string)
  if (val.matches(/^epsg:(\d{4,})$/i)) -> EPSG (first match of the regexp)
  else if (val.trim().startsWith('+')) -> Proj4
  else -> likely WKT
else if (val is integer) -> EPSG
else if (val is object/dict) -> PROJJSON
else -> invalid

or just do the following to convert epsg strings to int and pass the rest through:

if (val is string and (match = val.matches(/^epsg:(\d{4,})$/i))) 
  return Integer.parseString(match[1])
else
  return val

[m-mohr]

It would be great to get this small convenience into the Python client as all other clients already handle it smoothly:
Open-EO/openeo-processes#391 (comment)