Circle processor
- Circle processor

Circle processor

Converts circle definitions of shapes to regular polygons which approximate them.

Table 5. Circle Processor Options

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`
`description`	no	-	Description of the processor. Useful for describing the purpose of the processor or its configuration.
`if`	no	-	Conditionally execute the processor. See Conditionally run a processor.
`ignore_failure`	no	`false`	Ignore failures for the processor. See Handling pipeline failures.
`on_failure`	no	-	Handle failures for the processor. See Handling pipeline failures.
`tag`	no	-	Identifier for the processor. Useful for debugging and metrics.

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.

Circles that contain a pole are not supported.

Example: Circle defined in Well Known Text

In this example a circle defined in WKT format is indexed

PUT circles/_doc/1?pipeline=polygonize_circles
{
  "circle": "CIRCLE (30 10 40)"
}
GET circles/_doc/1

The response from the above index request:

{
  "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))"
  }
}

Example: Circle defined in GeoJSON

In this example a circle defined in GeoJSON format is indexed

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

The response from the above index request:

{
  "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"
    }
  }
}

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.

Table 6. Circle Processor Accuracy

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