atan2()

(PHP 4, PHP 5, PHP 7)

两个参数的反正切

说明

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

本函数计算两个变量$x和$y的反正切值。和计算$y/$x的反正切相似，只除了两个参数的符号是用来确定结果的象限之外。

本函数的结果为弧度，其值在-PI 和 PI 之间（包括-PI 和 PI）。

参数

$y

Dividend parameter

$x

Divisor parameter

返回值

$x和$y的反正切弧度值。

参见

• atan() 反正切

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. :)

<?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 °
*/
?>

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

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);
  }

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;
   
}
?>