Allow bounding box queries for geo-tagged entities

[acka47]

Requested by @aharth in the metadaten.community forum, see https://metadaten.community/t/bounding-box-abfragen-mit-lobid-gnd/1041:

gibt es eine Möglichkeit, mit dem lobid-gnd API nach Geo-Koordination zu filtern? Also Ergebnisse zurückliefern, die in einer Bounding Box liegen?

With the current elasticsearch setup and the current representation of geo coordinates in lobid-gnd data (directly taken over from DNB GND RDF), this does not work.

Example Köln (JSON):

  "hasGeometry" : [ {
    "type" : "Point",
    "asWKT" : [ "Point ( +006.950000 +050.933333 )" ]
  } ]

We would have to additionally (to be backwards compatible) record the geo coordinates like this (like we do for example with spatial subjects in NWBib):

      "geo" : {
        "lat" : "50.933333",
        "lon" : "6.950000"
      }

Note, that EntityFacts uses another approach than in the GND RDF, see https://hub.culturegraph.org/entityfacts/4031483-2:

   "location" : {
    "type" : "Feature",
    "geometry" : {
      "type" : "Point",
      "coordinates" : [ "6.950000", "50.933333" ]
    }
  }