Bounding Box Size

[Olivia]

Hi all,

 

I am using PHP 5.3.9 and I am trying to figure out how to calculate the size of a bounding box based on the passed in coordinates of the 4 corners of a geographical map.

The reason for this is that I need to check that the size/area of the bounding box is not larger than 20 Kilometres.

 

The bounding box format is defined as:

$southwest_lat = $_GET['swlat'];
$southwest_lng = $_GET['swlng'];
$northeast_lat =  $_GET['nelat'];
$northeast_lng = $_GET['nelng'];

Your help is much appreciated.

Kind regards,
Olivia

 

[Aaron Singline - Turboweb Limited]

Yay an actual question about PHP! :D

I think you'll need more data at the moment you seem to be only able to calculate a straight line as you have essentially got a x and y location for a start and finish.

http://www.movable-type.co.uk/scripts/latlong.html

Gives some yummy formulae to work with.  Javascript examples but I'm sure you can convert it easy enough. :)

Cheers,


Aaron

Aaron Singline (about me) Co-Founder / Support
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[Jason Kang]

I've found a good answer for you! :-D

http://bit.ly/11SaJ04

Or

$southwest_lat = $_GET['swlat'];
$southwest_lng = $_GET['swlng'];
$northeast_lat =  $_GET['nelat'];
$northeast_lng = $_GET['nelng'];

$result = distance($southwest_lat, $southwest_lng, $northeast_lat, $northeast_lng, "K");

if($result > 20) {

  echo "over 20!";

} else {

  echo "over 20!";

}

function distance($lat1, $lon1, $lat2, $lon2, $unit) {

  $theta = $lon1 - $lon2;
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);

  if ($unit == "K") {
    return ($miles * 1.609344);
  } else if ($unit == "N") {
      return ($miles * 0.8684);
    } else {
        return $miles;
      }
}

--

[Tim Oliver]

Area/size of the bounding box may not be distance between the two points - do you mean a bounding box that's aligned with edges parallel to latitude and longitude? And did you want distance less than 20km, area less than 20 square kilometers or some dimension less than 20km? This gets pretty hairy if the box can be large since the area of a 'rectangular' region on the sphere is larger than on a flat surface.

http://www.lunarpedia.org/index.php?title=Area_of_regions_on_the_lunar_sphere might be handy.

[Jason Kang]

oops sorry. My answer was about the distance, not space.

[anru]

This article may help to calculate size of bounding box. it is PHP based.

http://sgowtham.net/ramblings/2009/08/04/php-calculating-distance-between-two-locations-given-their-gps-coordinates/


regards,

anru

On 30/04/2013 4:30 p.m., Olivia wrote:

--

[Olivia Brown]

Hi Tim,

 

Yes I need to work out the area size of a rectangular (bounding box) on a geographical map given a Southwest latitude/longitude and a Northeast latitude/longitude geographic coordinate.

 

If the size of the bounding box is <= 20 kilometres than I retrieve all the rows from the database that are within that bounding box but if the bounding box is larger than 20 Kilometres than I display an error message (i.e. Area too large)

 

Thank you for everyone's help so far

On Tue, Apr 30, 2013 at 4:57 PM, Tim Oliver <t...@xi.co.nz> wrote:

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[Dmitrii Ruban]

Because in your case 20km is not much you can neglect that you are measuring the area on a sphere and consider it is flat. So just calculate the distance between two point on axel X and Y and then multiply them as you would do for basic rectangle.  

Using code below;