perturb lat,lon by fixed radius, added example for php nerds

perturbLatLon.js

const geolib = require('geolib')

// https://gis.stackexchange.com/questions/25877/generating-random-locations-nearby
const perturbedLatLon = (lat,lon,deltaM) => {
  const r = deltaM/111300 // = 100 meters
  const y0 = lat
  const x0 = lon
  const u = Math.random()
  const v = Math.random()
  const w = r * Math.sqrt(u)
  const t = 2 * Math.PI * v
  const x = w * Math.cos(t)
  const y1 = w * Math.sin(t)
  const x1 = x / Math.cos(y0)

  newY = y0 + y1
  newX = x0 + x1
  // console.log({ r:r, y0:y0, x0:x0, u:u, v:v, w:w, t:t, x:x, y1:y1, x1: x1, newY:newY, newX:newX })
  return [newY,newX]
}

if (process.argv.length < 4) {
  console.log('usage node perturbLatLon lat lon (deltaM opt)');
  process.exit(0);
}
let deltaM = 1000; // meters
const origLat = parseFloat(process.argv[2]);
const origLon = parseFloat(process.argv[3]);
if (process.argv.length >= 5) {
  deltaM = parseFloat(process.argv[4]);
}


for (let i=0;i < 1000;i++) {
  const point = perturbedLatLon(origLat,origLon,deltaM)
  const distance = geolib.getDistance({ latitude: origLat, longitude: origLon}, { latitude: point[0], longitude: point[1] });
  console.log({ origin: [origLat,origLon], newPoint: point, distanceMeters: distance })
}

perturbLatLon.php

<?php
    function perturbedLatLon($lat,$lon,$deltaM) {
      $r    = $deltaM/111300;
      $y0   = $lat;
      $x0   = $lon;
      $u    = mt_rand() / mt_getrandmax();
      $v    = mt_rand() / mt_getrandmax();
      $w    = $r * sqrt($u);
      $t    = 2 * pi() * $v;
      $x    = $w * cos($t);
      $y1   = $w * sin($t);
      $x1   = $x / cos($y0);

      $newY = $y0 + $y1;
      $newX = $x0 + $x1;
      // dbg('perturbedLatLon',[ 'r' => $r, 'y0' => $y0, 'x0' => $x0, 'u' => $u, 'v' => $v, 'w' => $w, 't' => $t, 'x' => $x, 'y1' => $y1, 'x1' => $x1, 'newLat' => $newY, 'newLon' => $newX ]);
      return [$newY,$newX];
    }