How to show distance from some point and apply decay funtion to it

[enp (Eugene Prokopiev)]

Hi,

It is possible to score destinations by distance from some point and even show something like distance itself:

  GET data/destination/_search?_source=city_name,location
  {
    "query": {
      "function_score": {
        "functions": [
          {
            "exp": {
              "location": {
                "origin": {
                  "lat": 51.50853,
                  "lon": -0.12574
                },
                "offset": "1km",
                "scale": "100km"
              }
            }
          }
        ]
      }
    },
    "script_fields": {
      "distance": {
        "script": "doc['location'].arcDistance(-0.12574,51.50853)"
      }
    }
  }

I see something like this as result:

  {
    "_index": "data",
    "_type": "destination",
    "_id": "477",
    "_score": 1,
    "_source": {
      "city_name": "London",
      "location": {
        "lon": "-0.12574",
        "lat": "51.50853"
      }
    },
    "fields": {
      "distance": [
        7492509.394966006
      ]
    }
  },
  {
    "_index": "data",
    "_type": "destination",
    "_id": "767",
    "_score": 0.90021527,
    "_source": {
      "city_name": "Kingston-Upon-Thames",
      "location": {
        "lon": "-0.300689",
        "lat": "51.41233"
      }
    },
    "fields": {
      "distance": [
        7497185.381104352
      ]
    }
  },
  {
    "_index": "data",
    "_type": "destination",
    "_id": "5696",
    "_score": 0.692497,
    "_source": {
      "city_name": "Henley-on-Thames",
      "location": {
        "lon": "-0.90503",
        "lat": "51.53758"
      }
    },
    "fields": {
      "distance": [
        7540166.626127409
      ]
    }
  }

My first problem is fields.distance value - it looks like not real distance in kilometers or even in meters. Maybe I need to convert result of arcDistance or use another function?

Another problem is scoring with decay function by distance instead of location. Is it possible? I tried to use 'distance' or 'fields.distance' instead of 'location' and some integer value for origin, but I got error "unknown field". Maybe another way exists?

I saw "geo_distance" filters support, but this is just filter without support of decay functions, right?