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    atan2

    (PHP 4, PHP 5, PHP 7, PHP 8)

    atan2 — 2 変数のアークタンジェント

    説明

    atan2(float $y, float $x): float

    この関数は、2 つの変数 x および y のアークタンジェントを計算します。 y / x のアークタンジェントを計算するのに似ていますが、 2 つの引数の符号を用いて結果の象限を定義することが異なっています。

    この関数は、結果を -PI から PI の間(両端を含む)のラジアンで返します。

    パラメータ

    y

    被除数。

    x

    除数。

    戻り値

    y/x のアークタンジェントをラジアンで返します。

    参考

    • atan() - 逆正接（アークタンジェント）

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    User Contributed Notes 5 notes

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    15
    reubs at idsdatanet dot com
    21 years ago
    Just a note:

    PHP's atan2 function receives parameters in (y,x) and Excel receives it in (x,y) format. Just in case you are porting formulas across. :)
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    9
    fred dot beck at rrd dot com
    15 years ago
    <?php
    /**
    *    Given an origin point of (0,0) and a destination point $x,$y
    *  somewhere on an axis grid, compass() determines the compass
    *  heading(direction) of the destination point from the origin
    *   
    *  HOWEVER, atan2(y,x)'s natural compass thinks east is north,
    *
    *  {135}-------{ 90}-------{45}
    *      | +-----[ +y]-----+ | 
    *      | |               | | 
    *      | |               | | 
    *  {180} [-x]  [0,0]  [+x] {0} <--------- North ?
    *      | |               | | 
    *      | |               | | 
    *      | +-----[ -y]-----+ |
    * {-135}-------{-90}-------{-45}
    *
    *
    *    SO, we simply transpose the (y,x) parameters to atan2(x,y)
    *     which will both rotate(left) and reflect(mirror) the compass.
    *
    *  Which gives us this compass
    *
    *  {-45}-------{ 0 }-------{45}
    *      | +-----[ +y]-----+ | 
    *      | |               | | 
    *      | |               | | 
    *  {-90} [-x]  [0,0]  [+x] {90}
    *      | |               | | 
    *      | |               | | 
    *      | +-----[ -y]-----+ |
    * {-135}-------{180}-------{135}
    *
    *  FINALLY,` we check if param $x was indeed a negative number,
    *  if so we simply add 360 to the negative angle returned by atan2()
    *   
    */
    function compass($x,$y)
        {
            if(    $x==0 AND $y==0){ return 0; } // ...or return 360
                return ($x < 0)
            ?     rad2deg(atan2($x,$y))+360      // TRANSPOSED !! y,x params
                : rad2deg(atan2($x,$y));
        }
    function     polar($x,$y)
        {
                $N = ($y>0)?'N':'';
                $S = ($y<0)?'S':'';
                $E = ($x>0)?'E':'';
                $W = ($x<0)?'W':'';       
            return     $N.$S.$E.$W;
        }
    function     show_compass($x,$y)
         {
             return     '<BR>'
                     .polar($x,$y)
                 .    ' compass( x='.$x.', y='.$y.' )= '
                     .number_format(compass($x,$y),3).'&deg';
         }

    echo     show_compass(0,3);
    echo     show_compass(.06,3);
    echo     show_compass(3,3);
    echo     show_compass(3,.06);
    echo     show_compass(3,0);
    echo     show_compass(3,-.06);
    echo     show_compass(3,-3);
    echo     show_compass(.06,-3);
    echo     show_compass(0,-3);
    echo     show_compass(-.06,-3);
    echo     show_compass(-3,-3);
    echo     show_compass(-3,-.06);
    echo     show_compass(-3,0);
    echo     show_compass(-3,.06);
    echo     show_compass(-3,3);
    echo     show_compass(-.06,3);

    /* RENDERS THIS

    N compass( x=0, y=3 )= 0 °
    NE compass( x=0.06, y=3 )= 1.14576283818 °
    NE compass( x=3, y=3 )= 45 °
    NE compass( x=3, y=0.06 )= 88.8542371618 °
    E compass( x=3, y=0 )= 90 °
    SE compass( x=3, y=-0.06 )= 91.1457628382 °
    SE compass( x=3, y=-3 )= 135 °
    SE compass( x=0.06, y=-3 )= 178.854237162 °
    S compass( x=0, y=-3 )= 180 °
    SW compass( x=-0.06, y=-3 )= 181.145762838 °
    SW compass( x=-3, y=-3 )= 225 °
    SW compass( x=-3, y=-0.06 )= 268.854237162 °
    W compass( x=-3, y=0 )= 270 °
    NW compass( x=-3, y=0.06 )= 271.145762838 °
    NW compass( x=-3, y=3 )= 315 °
    NW compass( x=-0.06, y=3 )= 358.854237162 °

    */

    ?>
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    1
    mirellastitan at gmail dot com
    7 years ago
    The russian translation for this article contains a translation error.

    Делитель and Делимое should be visa versa:

    Делимое is the dividend
    Делитель is the divisor

    Thank you in advance for fixing this issue. It's quite confusing
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    0
    Monte Shaffer
    17 years ago
    Here is a function that will return a new point [Rotate around non-origin pivot point]

    (x,y) is current point
    (cx,cy) is pivot point to rotate
    =a= is angle in degrees

        $_rotation     = 1;      # -1 = counter, 1 = clockwise
        $_precision    = 2;      # two decimal places

    function returnRotatedPoint($x,$y,$cx,$cy,$a)
        {
        # http://mathforum.org/library/drmath/view/63184.html
        global $_rotation;     # -1 = counter, 1 = clockwise
        global $_precision;    # two decimal places

       
                // radius using distance formula
                $r = sqrt(pow(($x-$cx),2)+pow(($y-$cy),2));
                // initial angle in relation to center
                $iA = $_rotation * rad2deg(atan2(($y-$cy),($x-$cx)));

                $nx = number_format($r * cos(deg2rad($_rotation * $a + $iA)),$_precision);
                $ny = number_format($r * sin(deg2rad($_rotation * $a + $iA)),$_precision);

        return array("x"=>$cx+$nx,"y"=>$cy+$ny);
        }
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    -2
    andyidol at gmail dot com
    14 years ago
    This function will return degree by vertex coordinates in general trigonometrical coordinate system where zero is located at position (1, 0), 90' at (0, 1), 180' at (-1, 0) and so on.

    <?php

    function GetDegree($x, $y)
    {
          // we don't want to cause division by zero
          if($x == 0) $x = 1 / 10000;
         
          $deg = rad2deg(atan(abs($y / $x)));
         
      if(    $y >= 0) $deg = $x < 0 ? 180 - $deg : $deg;
      else            $deg = $x < 0 ? 180 + $deg : 360 - $deg;
         
      return     $deg;
         
    }

    ?>
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