Add random points

Save this as add_random_points.php and use it as outlined in the video tutorial here: https://www.patreon.com/posts/31650405

<?php

/*

   This script adds random deviation to the polygons in a geojson file
   intended to be used as described in https://www.patreon.com/posts/31650405

   (C)2019 by Tom Vogt <tom@lemuria.org>

   Support me on Patreon:
   https://www.patreon.com/notveryprofessional

• /

$max_deviation = 0.2; $max_abs = 0.02; $min_distance = 0.05;

$iterations = 4;

if ($argc < 2 ) {

   exit( "Usage: add_random_points.php <filename.json>\n" );

}

// FIXME: This script created a few cases of self-intersection that must be fixed manually // in QGIS: Vector -> Geometry Tools -> Check Validity

$cells = json_decode(file_get_contents($argv[1]), true);

for ($i=0; $i<$iterations; $i++) {

   $lookup = array();

   foreach ($cells['features'] as &$cell) {
       $points = $cell['geometry']['coordinates'][0];

       $prev = null;
       $newpoints = array();

       foreach ($points as $point) {
           if ($prev) {
               $distance = sqrt(pow($prev[0] - $point[0], 2) + pow($prev[1] - $point[1], 2));
               if ($distance == 0) continue;

               if ($distance > $min_distance) {
                   $id_a = $prev[0]."-".$prev[1];
                   $id_b = $point[0]."-".$point[1];

                   if (isset($lookup[$id_a."--".$id_b])) {
                       $newpoints[] = $lookup[$id_a."--".$id_b];
                   } elseif (isset($lookup[$id_b."--".$id_a])) {
                           $newpoints[] = $lookup[$id_b."--".$id_a];
                   } else {
                       $x = ($prev[0]+$point[0])/2.0;
                       $y = ($prev[1]+$point[1])/2.0;

                       $r = mt_rand() / mt_getrandmax(); // 0-1
                       $r = ($r+1) / 2; // 0.5 - 1.0

                       // if we define dx=x2-x1 and dy=y2-y1, then the normals are (-dy, dx) and (dy, -dx).
                       $dx = $point[0] - $x;
                       $dy = $point[1] - $y;

                       if (mt_rand() / mt_getrandmax() < 0.5) {
                           $x_off = -$dy;
                           $y_off = $dx;
                       } else {
                           $x_off = $dy;
                           $y_off = -$dx;
                       }

                       $x_off *= $r * $max_deviation;
                       $x_off = max(min($x_off, $max_abs), $max_abs*-1);

                       $y_off *= $r * $max_deviation;
                       $y_off = max(min($y_off, $max_abs), $max_abs*-1);

                       $p = array($x + $x_off, $y + $y_off);
                       $lookup[$id_a."--".$id_b] = $p;
                       $newpoints[] = $p;
                   }
               }
           }
           $newpoints[] = $point;
           $prev = $point;
       }
       $cell['geometry']['coordinates'][0] = $newpoints;
   }

}

echo json_encode($cells, JSON_PRETTY_PRINT);

?>