PHP 5.5.16 is released

atan2

(PHP 4, PHP 5)

atan2Arc tangent of two variables

Description

float atan2 ( float $y , float $x )

This function calculates the arc tangent of the two variables x and y. It is similar to calculating the arc tangent of y / x, except that the signs of both arguments are used to determine the quadrant of the result.

The function returns the result in radians, which is between -PI and PI (inclusive).

Parameters

y

Dividend parameter

x

Divisor parameter

Return Values

The arc tangent of y/x in radians.

See Also

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User Contributed Notes 4 notes

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1
fred dot beck at rrd dot com
5 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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0
andyidol at gmail dot com
4 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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0
Monte Shaffer
7 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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0
reubs at idsdatanet dot com
11 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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