I'm trying to implement the kml circle generator (from http://bbs.keyhole.com/ubb/showthreaded.php/Cat/0/Number/23634/page/) in perl, but the results are horribly wrong due to what appears to be rounding errors. Since the only changes will be to the least significant digits, I end up with a long string of the same number:

Here's the relevent section of my script:

  $lat1 = deg2rad($bestlat);
  $long1 = deg2rad($bestlong);
  $lat2 = deg2rad($minlat);
  $long2 = deg2rad($minlong);
  $dlat = $lat2 - $lat1;
  $dlong = $long2 - $long1;
  $a = ((sin($dlat/2)) ** 2) + cos($lat1) * cos($lat2) * ((sin($dlong/
+2)) ** 2);
  $c = 2 * atan2(sqrt($a), sqrt(1-$a));
  #get distance between points (in meters)
  $d = 6378137 * $c;
  for($i=0;$i<=360;$i++)
  {
    $radial = deg2rad($i);
    $lat_rad = asin(sin($lat1) * cos($d_rad) + cos($lat1) * sin($d_rad
+) * cos($radial));
    $dlon_rad = atan2(sin($radial) * sin($d_rad) * cos($lat1), cos($d_
+rad)-sin($lat1) * sin($lat_rad));
    $lon_rad = fmod(($long1 + $dlon_rad + pi()),
                                    2 * pi()) - pi();
    print rad2deg($lon_rad).",".rad2deg($lat_rad).",0 ";
  }

[download]

And here's the sort of thing I get out of it:

-123.003,49.2681,0 -123.003,49.2681,0 -123.003,49.2681,0 ...

It should be something along the lines of:

-122.891991,49.254269432823,0 -122.89197200398,49.254269324619,0 -122.89195301375,49.25426900004,0 -122.8919340351,49.254268459185,0

In reply to Trigonometry in perl by Anonymous Monk

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