atan2

(PHP 4, PHP 5)

atan2 — 两个参数的反正切

说明

float atan2 ( float $y , float $x )

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）。

参见 acos() 和 atan()。

PHP手册 - N: 两个参数的反正切

用户评论:

Anonymous (27-Jan-2012 07:59)

the description of this function seems not to be properly right. i do not obtain the arc tangent of y/x in radians, but the arc tangent of x/y. probably a little mistake in writing this part of the manual.

andyidol at gmail dot com (10-Aug-2010 04:18)

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; } ?>

fred dot beck at rrd dot com (11-Jan-2009 08:39)

<?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 ° */ ?>

Monte Shaffer (08-Jun-2007 07:35)

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); }

reubs at idsdatanet dot com (23-May-2003 09:01)

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. :)