$atan2 (aggregation)

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$atan2

New in version 4.2.在版本4.2中新增。

Returns the inverse tangent (arc tangent) of y / x, where y and x are the first and second values passed to the expression respectively.返回y/x的反切线（反正切），其中y和x分别是传递给表达式的第一个和第二个值。

$atan2 has the following syntax:语法如下：

{ $atan2: [ <expression 1>, <expression 2> ] }

$atan2 takes any valid expression that resolves to a number.接受解析为数字的任何有效表达式。

$atan2 returns values in radians. 返回以弧度为单位的值。Use $radiansToDegrees operator to convert the output value from radians to degrees.使用$radiansToDegrees运算符将输出值从弧度转换为度。

By default $atan2 returns values as a double. 默认情况下，$atan2以double返回值。$atan2 can also return values as a 128-bit decimal as long as the <expression> resolves to a 128-bit decimal value.只要<expression>解析为128位十进制值，也可以以128位十进制返回值。

For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

null and NaN

If the first argument to $atan2 is null, $atan2 returns null. 如果$atan2的第一个参数为null，$atan2返回null。If the first argument to $atan2 is NaN, $atan2 returns NaN. 如果$atan2的第一个参数是NaN，$atan2返回NaN。If the first argument resolves to a number and the second argument resolves to either NaN or null, $atan2 returns the NaN or null respectively.如果第一个参数解析为数字，而第二个参数则解析为NaN或null，$atan2分别返回NaN或null。

Example示例Results结果

{ $atan2: [ NaN, <value> ] }

or

{ $atan2: [ <value>, NaN ] }

NaN

{ $atan2: [ null, <value> ] }

or

{ $atan2: [ <value>, null ] }

null

Example示例

The trigonometry collection contains a document that stores three sides of a right-angle triangle:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "side_a" : NumberDecimal("3"),
  "side_b" : NumberDecimal("4"),
  "hypotenuse" : NumberDecimal("5")
}

The following aggregation operation uses the $atan2 expression to calculate the angle adjacent to side_a and add it to the input document using the $addFields pipeline stage.

db.trigonometry.aggregate([
  {
    $addFields : {
      "angle_a" : {
        $radiansToDegrees : {
          $atan2 : [ "$side_b", "$side_a" ]
        }
      }
    }
  }
])

The $radiansToDegrees expression converts the radian value returned by $atan2 to the equivalent value in degrees.

The command returns the following output:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "side_a" : NumberDecimal("3"),
  "side_b" : NumberDecimal("4"),
  "hypotenuse" : NumberDecimal("5"),
  "angle_a" : NumberDecimal("53.13010235415597870314438744090658")
}

Since side_b and side_a are stored as 128-bit decimals, the output of $atan2 is a 128-bit decimal.

The trigonometry collection contains a document that stores three sides of a right-angle triangle:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "side_a" : NumberDecimal("3"),
  "side_b" : NumberDecimal("4"),
  "hypotenuse" : NumberDecimal("5")
}

The following aggregation operation uses the $atan2 expression to calculate the angle adjacent to side_a and add it to the input document using the $addFields pipeline stage.

db.trigonometry.aggregate([
  {
    $addFields : {
      "angle_a" : {
        $atan2 : [ "$side_b", "$side_a" ]
      }
    }
  }
])

The command returns the following output:

{
  "_id" : ObjectId("5c50782193f833234ba90d85"),
  "side_a" : NumberDecimal("3"),
  "side_b" : NumberDecimal("4"),
  "hypotenuse" : NumberDecimal("5"),
  "angle_a" : NumberDecimal("0.9272952180016122324285124629224287")
}

Since side_b and side_a are stored as 128-bit decimals, the output of $atan2 is a 128-bit decimal.

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