$center¶

Definition定义¶

$center¶

The $center operator specifies a circle for a $geoWithin query. The query returns legacy coordinate pairs that are within the bounds of the circle. The operator does not return GeoJSON objects.

To use the $center operator, specify an array that contains:

• The grid coordinates of the circle’s center point, and
• The circle’s radius, as measured in the units used by the coordinate system.

{
   <location field>: {
      $geoWithin: { $center: [ [ <x>, <y> ] , <radius> ] }
   }
}

Important

If you use longitude and latitude, specify longitude first.

Behavior行为¶

The query calculates distances using flat (planar) geometry.

Applications can use $center without having a geospatial index. However, geospatial indexes support much faster queries than the unindexed equivalents.

Only the 2d geospatial index supports $center.

Example示例¶

The following example query returns all documents that have coordinates that exist within the circle centered on [ -74, 40.74 ] and with a radius of 10:

db.places.find(
   { loc: { $geoWithin: { $center: [ [-74, 40.74], 10 ] } } }
)