OPTIONS

$geoNear (aggregation)

Definition

$geoNear

New in version 2.4.

$geoNear returns documents in order of nearest to farthest from a specified point and pass the documents through the aggregation pipeline. You can only use $geoNear as the first stage of a pipeline.

The $geoNear operator accepts a document that contains the following fields. Specify all distances in the same units as those of the processed documents’ coordinate system:

Field Type Description
limit number Optional. The maximum number of documents to return. The default value is 100. See also the num option.
num number Optional. The num option provides the same function as the limit option. Both define the maximum number of documents to return. If both options are included, the num value overrides the limit value.
query document Optional. Limits the results to the documents that match the query. The query syntax is the usual MongoDB read operation query syntax.
spherical Boolean

Required if using a 2dsphere index. For use with 2dsphere indexes, spherical must be true.

The default value is false.

distanceMultiplier number Optional. The factor to multiply all distances returned by the query. For example, use the distanceMultiplier to convert radians, as returned by a spherical query, to kilometers by multiplying by the radius of the Earth.
uniqueDocs Boolean Optional. If this value is true, the query returns a matching document once, even if more than one of the document’s location fields match the query. If this value is false, the query returns a document multiple times if the document has multiple matching location fields. See $uniqueDocs for more information.
near GeoJSON point or legacy coordinate pairs The point for which to find the closest documents.
distanceField string The output field that contains the calculated distance. To specify a field within a subdocument, use dot notation.
maxDistance number Optional. A distance from the center point. Specify the distance in radians. MongoDB limits the results to those documents that fall within the specified distance from the center point.
includeLocs string Optional. This specifies the output field that identifies the location used to calculate the distance. This option is useful when a location field contains multiple locations. To specify a field within a subdocument, use dot notation.

Behavior

When using $geoNear, consider that:

  • You must include the distanceField option. The distanceField option specifies the field that will contain the calculated distance.
  • The collection must have a geospatial index.
  • The $geoNear requires that a collection have at most only one 2d index and/or only one 2dsphere index.
  • If using a 2dsphere index, you must specify spherical: true.

The options for $geoNear are similar to the geoNear command with the following exceptions:

  • distanceField is a mandatory field for the $geoNear pipeline operator; the option does not exist in the geoNear command.
  • includeLocs accepts a string in the $geoNear pipeline operator and a boolean in the geoNear command.

Example

Consider a collection places that has a 2dsphere index. The following aggregation finds at most 5 unique documents with a location at most 2 units from the center [ -73.99279 , 40.719296 ] and have type equal to public:

db.places.aggregate([
    {
      $geoNear: {
         near : { type : "Point", coordinates : [ -73.99279 , 40.719296 ] },
         distanceField: "dist.calculated",
         maxDistance: 2,
         query: { type: "public" },
         includeLocs: "dist.location",
         uniqueDocs: true,
         num: 5,
         spherical: true
      }
    }
])

The aggregation returns the following:

{
   "result" : [
      {
        "_id" : 8,
        "name" : "Sara D. Roosevelt Park",
        "type" : "public",
        "location" : {
            "type" : "Point",
            "coordinates" : [ -73.9928, 40.7193 ]
         },
         "dist" : {
            "calculated" : 0.9546646278778689,
            "location" : {
               "type": "Point",
               "coordinates" : [ -73.9928, 40.7193 ]
            }
         }
      }
   ],
   "ok" : 1
}

The document in the result array contains two new fields:

  • dist.calculated field that contains the calculated distance, and
  • dist.location field that contains the location used in the calculation.