Posted by "Kristen G. Thorson" on 08/03/05 18:58

See

http://us3.php.net/manual/en/language.operators.php
http://us3.php.net/manual/en/language.operators.bitwise.php


You want this:

function calc_distance($curX,$curY,$newX,$newY) {
// calculate distance to new location
$distX = abs($curX - $newX);
$distY = abs($curY - $newY);

if ($distX <= 150 && $distY <= 150) {
$dist = sqrt(pow( $distX,2) + pow($distY,2));
} elseif ($distX > 150 && $distY <= 150) {
$dist = sqrt(pow((abs(300 - $newX)),2) + pow($distY,2));
} elseif ($distX <= 150 && $distY > 150) {
$dist = sqrt(pow($distX,2) + pow((abs(300 - $newY)),2));
} else {
$dist = sqrt(pow((abs(300 - $newX)),2) + pow((abs(300 - $newY)),2));
}

return $dist;
}

echo calc_distance( 150, 150, 300, 300 ); //echoes 212.13203435596
echo "<br>150^2=".(150^2)." and pow(150,2)=".(pow(150,2)); //echoes
150^2=148 and pow(150,2)=22500




kgt




Rene Brehmer wrote:

>I've run into a situation where PHP is way off when doing a relatively
>simple calculation of distance between two points in 2-dimensional space,
>where coordinates go from 1 to 300 in both X and Y directions. When passing
>300, it goes back to 1, and vise-versa (it's for a game and is supposed to
>approximate the movement over a sphere).
>
>Using this function:
>
>function calc_distance($curX,$curY,$newX,$newY) {
> // calculate distance to new location
> $distX = abs($curX - $newX);
> $distY = abs($curY - $newY);
>
> if ($distX <= 150 && $distY <= 150) {
> $dist = sqrt($distX^2 + $distY^2);
> } elseif ($distX > 150 && $distY <= 150) {
> $dist = sqrt((abs(300 - $newX))^2 + $distY^2);
> } elseif ($distX <= 150 && $distY > 150) {
> $dist = sqrt($distX^2 + (abs(300 - $newY))^2);
> } else {
> $dist = sqrt((abs(300 - $newX))^2 + (abs(300 - $newY))^2);
> }
>
> return $dist;
>}
>
>And using 150,150 as $curX,$curY and 300,300 as $newX,$newY ... PHP
>calculates $dist as 3.46410161514
>which obviously is far off target ...referring to my calcultor, the correct
>result for the same code is supposed to be 212.1320
>
>What happens here ? And how the heck do I get to calculate right ?
>
>Float errors usually isn't this severe, so I'm assuming it's a problem with
>properly acknowledging the hierarchi of the mathematical operators ...
>
>It's PHP ver. 4.3.0, on Apache/2.0.53 (Win32), on WinXP SP1
>
>I've been trying to manually calculate the formula out of order to figure
>out how the strange result comes about, but haven't had any success yet ...
>
>Any suggestions ?
>
>Rene
>
>

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