a gradient of random points?

filn

so here is my really lame random number script to generate X,Y,Z coordinates to create a point cloud. i wanted it to be as random as possible, but it really comes out way to even.

<?


// starting point for loop count
$loop_start = '0';

// setup number of point sets to generate
$num_of_points = "100";

while ($loop_start <= $num_of_points) {


// generate random numbers for point cloud
$random1 = rand(0, 1000);
$random2 = rand(0, 1000);
$random3 = rand(0, 1000);
$random4 = rand(0, 1000);
$random5 = rand(0, 1000);
$random6 = rand(0, 1000);

$point1 = rand($random1, $random2);
$point2 = rand($random3, $random4);
$point3 = rand($random5, $random6);

// echo points to screen
echo "$point1,$point2,$point3 <br/>";

// increase loop count
$loop_start++;

} 

?>

the distribution of points in the field is way to even. i want it to be denser in some places and open in others. can somebody help me make my random points more random and less evenly spread out in the field. thanks!

Installer

Using random numbers generated randomly like that does nothing to increase the randomness or even the range of the random numbers. It's merely redundant. Just using "$point1 = rand(0, 1000)", etc. will give you indistinguishable results. But use "mt_rand()" instead of "rand()"

filn

thanks, i made the changed you suggested.

whats the diffrence between mt_rand() and rand()?

i notice a big diffrence in the way mt_rand() distributes the points.

Installer

As far as I know, "mt_rand()" produces a more random-like return due to using a better algorithm. It also doesn't need to be seeded.

Weedpacket

rand() uses whatever random number generator was supplied by the C library used to compile the program (and some of those libraries are awful). mt_rand() is a cross-platform generator with probably nicer statistics (and certainly runs the same on all platforms). (PS: by "as random as possible" I assume you mean "uniform").

filn

i still feel like it spreads the points out too evenly around the space.

any suggestions on how i could mix it up even more?

Weedpacket

Use more points? You're only picking 100 out of a billion....

filn

Weedpacket wrote:
Use more points? You're only picking 100 out of a billion....

ive used various ammounts. it always spreads them out more or less evenly. there is never a large group points or a big open space, its always a few points relatively close together but thats about as dense as it gets. i would like to create a random point cloud that had some density to it in some places and less density in others, but all i get is a more or less even distribution through the space.

Installer

What you describe as your results sounds like expected behavior to me. The groupings you want sounds more like non-random results. Maybe you could simulate that by using much the same code as your original, except keep each "preliminary" range for a random number of iterations. Something like this:

$loop_start = '0'; 
$num_of_points = "100"; 
while ($loop_start <= $num_of_points) { 
    $random1 = mt_rand(0, 1000); 
    $random2 = mt_rand(0, 1000); 
    $random3 = mt_rand(0, 1000); 
    $random4 = mt_rand(0, 1000); 
    $random5 = mt_rand(0, 1000); 
    $random6 = mt_rand(0, 1000); 

$iter = mt_rand(1, 10);
$i = 0;
while (($i++ < $iter) && ($loop_start++ <= $num_of_points)) {
    $point1 = mt_rand($random1, $random2); 
    $point2 = mt_rand($random3, $random4); 
    $point3 = mt_rand($random5, $random6); 
    echo $point1 . ', ' . $point2 . ', ' . $point3 . '<br/>'; 
} 
}