[Geoserver-devel] Complex features - Encoding XML attributes in GeoJSON

[Nuno Miguel Carvalho Oliveira]

Dear all,

Currently, the complex features GeoJSON encoder [1] doesn't encode XML
(GML) attributes. For example, something like:

(...)
<gsml:positionalAccuracy>
  <gsml:CGI_NumericValue>
    <gsml:principalValue *uom="urn:ogc:def:uom:UCUM:m"*>*200.0*
</gsml:principalValue>
  </gsml:CGI_NumericValue>
</gsml:positionalAccuracy>
(...)

Will be encoded like this in GeoJSON:

(...)
"properties": {
    "gsml:positionAccuracy": {
        "gsml:CGI_NumericValue": {
            "gsml:principalValue": *100*
        }
    }
}
(...)

As far as I know, there is no standard or specification that defines how
the concept of complex features attributes (GML attributes) should be
encoded, the GeoJSON specification is quite permissible:



*A Feature object has a member with the name "properties". The value
of the properties member is an object (any JSON object or a JSON null
value).*

My suggestion is to encode XML\GML attributes as an array of values, using
the example  above:

(...)
"properties": {
    "gsml:positionAccuracy": {
        "gsml:CGI_NumericValue": {
            "gsml:principalValue": [



*100.0,                {                    "uom":
"urn:ogc:def:uom:UCUM:m"                }*
            ]
        }
    }
}
(...)

So, simple values (like 100.0) represent the value of the node and objects
(like *{"uom": "urn:ogc:def:uom:UCUM:m"}*) represent the attributes of the
node. This keeps the semantic and doesn't add too much burden to the
clients.

Any feedback \ comments on this are welcome :)

Kind regards,

Nuno Oliveira

[1]
https://github.com/geoserver/geoserver/blob/master/src/wfs/src/main/java/org/geoserver/wfs/json/ComplexGeoJsonWriter.java


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