atan2

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

atan2 —Arc tangent of two variables

Description

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

This function calculates the arc tangent of the two variablesx andy. It is similar to calculating the arc tangent ofy /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 ofy/x in radians.

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User Contributed Notes2 notes

down

reubs at idsdatanet dot com ¶

22 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. :)

down

fred dot beck at rrd dot com ¶

16 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 $x was indeed a negative number,
 *  if so we simply add 360 to the negative angle returned by atan2()
 *
 */
functioncompass($x,$y)
    {
        if($x==0AND$y==0){ return0; }// ...or return 360
return ($x<0)
        ?rad2deg(atan2($x,$y))+360// TRANSPOSED !! y,x params
:rad2deg(atan2($x,$y));
    }
functionpolar($x,$y)
    {
$N= ($y>0)?'N':'';
$S= ($y<0)?'S':'';
$E= ($x>0)?'E':'';
$W= ($x<0)?'W':'';
        return$N.$S.$E.$W;
    }
functionshow_compass($x,$y)
     {
         return'<BR>'
.polar($x,$y)
             .' compass( x='.$x.', y='.$y.' )= '
.number_format(compass($x,$y),3).'&deg';
     }

echoshow_compass(0,3);
echoshow_compass(.06,3);
echoshow_compass(3,3);
echoshow_compass(3,.06);
echoshow_compass(3,0);
echoshow_compass(3,-.06);
echoshow_compass(3,-3);
echoshow_compass(.06,-3);
echoshow_compass(0,-3);
echoshow_compass(-.06,-3);
echoshow_compass(-3,-3);
echoshow_compass(-3,-.06);
echoshow_compass(-3,0);
echoshow_compass(-3,.06);
echoshow_compass(-3,3);
echoshow_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 °

*/

?>