[role="xpack"]
[testenv="basic"]
[[ingest-circle-processor]]
=== Circle Processor
Converts circle definitions of shapes to regular polygons which approximate them.

[[circle-processor-options]]
.Circle Processor Options
[options="header"]
|======
| Name                        | Required  | Default  | Description
| `field`                     | yes       | -        | The string-valued field to trim whitespace from
| `target_field`              | no        | `field`  | The field to assign the polygon shape to, by default `field` is updated in-place
| `ignore_missing`            | no        | `false`  | If `true` and `field` does not exist, the processor quietly exits without modifying the document
| `error_distance`            | yes       | -        | The difference between the resulting inscribed distance from center to side and the circle's radius (measured in meters for `geo_shape`, unit-less for `shape`)
| `shape_type`                | yes       | -        | which field mapping type is to be used when processing the circle: `geo_shape` or `shape`
include::common-options.asciidoc[]
|======


image:images/spatial/error_distance.png[]

[source,console]
--------------------------------------------------
PUT circles
{
  "mappings": {
    "properties": {
      "circle": {
        "type": "geo_shape"
      }
    }
  }
}

PUT _ingest/pipeline/polygonize_circles
{
    "description": "translate circle to polygon",
    "processors": [
      {
        "circle": {
          "field": "circle",
          "error_distance": 28.0,
          "shape_type": "geo_shape"
        }
      }
    ]
}
--------------------------------------------------

Using the above pipeline, we can attempt to index a document into the `circles` index.
The circle can be represented as either a WKT circle or a GeoJSON circle. The resulting
polygon will be represented and indexed using the same format as the input circle. WKT will
be translated to a WKT polygon, and GeoJSON circles will be translated to GeoJSON polygons.

==== Example: Circle defined in Well Known Text

In this example a circle defined in WKT format is indexed

[source,console]
--------------------------------------------------
PUT circles/_doc/1?pipeline=polygonize_circles
{
  "circle": "CIRCLE (30 10 40)"
}

GET circles/_doc/1
--------------------------------------------------
// TEST[continued]

The response from the above index request:

[source,js]
--------------------------------------------------
{
  "found": true,
  "_index": "circles",
  "_type": "_doc",
  "_id": "1",
  "_version": 1,
  "_seq_no": 22,
  "_primary_term": 1,
  "_source": {
    "circle": "polygon ((30.000365257263184 10.0, 30.000111397193788 10.00034284530941, 29.999706043744222 10.000213571721195, 29.999706043744222 9.999786428278805, 30.000111397193788 9.99965715469059, 30.000365257263184 10.0))"
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"_seq_no": \d+/"_seq_no" : $body._seq_no/ s/"_primary_term": 1/"_primary_term" : $body._primary_term/]

==== Example: Circle defined in GeoJSON

In this example a circle defined in GeoJSON format is indexed

[source,console]
--------------------------------------------------
PUT circles/_doc/2?pipeline=polygonize_circles
{
  "circle": {
    "type": "circle",
    "radius": "40m",
    "coordinates": [30, 10]
  }
}

GET circles/_doc/2
--------------------------------------------------
// TEST[continued]

The response from the above index request:

[source,js]
--------------------------------------------------
{
  "found": true,
  "_index": "circles",
  "_type": "_doc",
  "_id": "2",
  "_version": 1,
  "_seq_no": 22,
  "_primary_term": 1,
  "_source": {
    "circle": {
      "coordinates": [
        [
          [30.000365257263184, 10.0],
          [30.000111397193788, 10.00034284530941],
          [29.999706043744222, 10.000213571721195],
          [29.999706043744222, 9.999786428278805],
          [30.000111397193788, 9.99965715469059],
          [30.000365257263184, 10.0]
        ]
      ],
      "type": "polygon"
    }
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"_seq_no": \d+/"_seq_no" : $body._seq_no/ s/"_primary_term": 1/"_primary_term" : $body._primary_term/]


==== Notes on Accuracy

Accuracy of the polygon that represents the circle is defined as `error_distance`. The smaller this
difference is, the closer to a perfect circle the polygon is.

Below is a table that aims to help capture how the radius of the circle affects the resulting number of sides
of the polygon given different inputs.

The minimum number of sides is `4` and the maximum is `1000`.

[[circle-processor-accuracy]]
.Circle Processor Accuracy
[options="header"]
|======
| error_distance | radius in meters   | number of sides of polygon
| 1.00           | 1.0                | 4
| 1.00           | 10.0               | 14
| 1.00           | 100.0              | 45
| 1.00           | 1000.0             | 141
| 1.00           | 10000.0            | 445
| 1.00           | 100000.0           | 1000
|======