- Indexes >
- Indexing Tutorials >
- Geospatial Index Tutorials >
- Calculate Distance Using Spherical Geometry
Calculate Distance Using Spherical Geometry¶
On this page
Note
While basic queries using spherical distance are supported by
the 2d
index, consider moving to a 2dsphere
index if your
data is primarily longitude and latitude.
The 2d
index supports queries that calculate distances on a
Euclidean plane (flat surface). The index also supports the following
query operators and command that calculate distances using spherical
geometry:
$nearSphere
$centerSphere
$near
geoNear
command with the{ spherical: true }
option.
Important
These three queries use radians for distance. Other query types do not.
For spherical query operators to function properly, you must convert distances to radians, and convert from radians to the distances units used by your application.
To convert:
- distance to radians: divide the distance by the radius of the sphere (e.g. the Earth) in the same units as the distance measurement.
- radians to distance: multiply the radian measure by the radius of the sphere (e.g. the Earth) in the units system that you want to convert the distance to.
The radius of the Earth is approximately 3,959
miles or
6,371
kilometers.
The following query would return documents from the places
collection within the circle described by the center [ -74, 40.74 ]
with a radius of 100
miles:
You may also use the distanceMultiplier
option to the
geoNear
to convert radians in the mongod
process, rather than in your application code. See distance
multiplier.
The following spherical query, returns all documents in the
collection places
within 100
miles from the point [ -74,
40.74 ]
.
The output of the above command would be:
Warning
Spherical queries that wrap around the poles or at the transition
from -180
to 180
longitude raise an error.
Note
While the default Earth-like bounds for geospatial indexes are
between -180
inclusive, and 180
, valid values for latitude
are between -90
and 90
.
Distance Multiplier¶
The distanceMultiplier
option of the geoNear
command returns
distances only after multiplying the results by an assigned value. This allows
MongoDB to return converted values, and removes the requirement to
convert units in application logic.
Using distanceMultiplier
in spherical queries provides results from
the geoNear
command that do not need radian-to-distance
conversion. The following example uses distanceMultiplier
in the
geoNear
command with a spherical example:
The output of the above operation would resemble the following: