# atan2

(PHP 4, PHP 5)

atan2Arc tangent of two variables

### Опис

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).

### Параметри

y

Dividend parameter

x

Divisor parameter

### Значення, що повертаються

The arc tangent of y/x in radians.

### User Contributed Notes 5 notes

12
reubs at idsdatanet dot com
19 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. :)
fred dot beck at rrd dot com
13 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

}
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 °

*/

?>
mirellastitan at gmail dot com
5 years ago

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
Monte Shaffer
15 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

\$r = sqrt(pow((\$x-\$cx),2)+pow((\$y-\$cy),2));
// initial angle in relation to center

\$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);
}
-1
andyidol at gmail dot com
11 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;