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$atan2

New from version 8.0.1.

The $atan2 operator in Amazon DocumentDB returns the inverse tangent (arc tangent) of y / x, where y and x are the first and second values passed to the expression respectively.

Both expressions must resolve to numeric values. The operator uses the sign of both arguments to determine the correct quadrant.

The result is in radians. To obtain degrees, apply $radiansToDegrees to the output.

The return type is double by default. If the inputs are 128-bit decimals, the output is also a 128-bit decimal.

Parameters

Behavior

null and NaN

If either argument is null (or references a missing field), the result is null. If either argument is NaN, the result is NaN. When one argument is null and the other is NaN, null takes precedence.

Example (MongoDB Shell)

The following example shows how to use the $atan2 operator to calculate the arctangent of y/x for a set of points.

Create sample documents

db.points.insertMany([
  { "_id": 1, "y": 1, "x": 1 },
  { "_id": 2, "y": 1, "x": 0 },
  { "_id": 3, "y": -1, "x": -1 }
]);

Query example

db.points.aggregate([
  { $project: {
    "angle": { $atan2: ["$y", "$x"] }
  }}
]);

Output

[
  { "_id": 1, "angle": 0.7853981633974483 },
  { "_id": 2, "angle": 1.5707963267948966 },
  { "_id": 3, "angle": -2.356194490192345 }
]

Code examples

To view a code example for using the $atan2 operator, choose the tab for the language that you want to use:

Node.js

const { MongoClient } = require('mongodb');

async function main() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const collection = db.collection('points');

  const result = await collection.aggregate([
    { $project: {
      "angle": { $atan2: ["$y", "$x"] }
    }}
  ]).toArray();

  console.log(result);
  await client.close();
}

main();

Python

from pymongo import MongoClient

def main():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client['test']
    collection = db['points']

    result = list(collection.aggregate([
        { '$project': {
            'angle': { '$atan2': ['$y', '$x'] }
        }}
    ]))

    print(result)
    client.close()

if __name__ == "__main__":
    main()