function farm_map_lon_deg_len in farmOS 7

Calculate longitude degree length at a given latitude. Equations are taken from https://en.wikipedia.org/wiki/Geographic_coordinate_system#Expressing_la... See also http://gis.stackexchange.com/questions/75528/length-of-a-degree-where-do...

Parameters

$lat: The latitude to calculate degree length at, in degrees.

Return value

string Returns the length of a degree of longitude at the given latitude as a string, in meters.

2 calls to farm_map_lon_deg_len()

farm_map_distance in modules/farm/farm_map/farm_map.geo.inc

Calculate the distance between two latitude/longitude points in meters.

farm_map_polygon_area in modules/farm/farm_map/farm_map.geo.inc

Calculate the area of a Polygon in square meters.

File

modules/farm/farm_map/farm_map.geo.inc, line 223

Farm map geometry functions.

Code

function farm_map_lon_deg_len($lat) {

  // Load GeoPHP.
  geophp_load();

  // Set BCMath scale.
  farm_map_set_bcscale();

  // Convert degrees to radians.
  $lat = deg2rad($lat);

  // Define coefficients. These are copied from
  // http://gis.stackexchange.com/questions/75528/length-of-a-degree-where-do-the-terms-in-this-formula-come-from
  $p1 = 111412.87733;
  $p2 = 93.50412;
  $p3 = 0.11774;

  // If BCMath is available, use that. Otherwise, use normal PHP float
  // operations.
  if (geoPHP::bcmathInstalled()) {
    $length = bcsub(bcmul($p1, cos($lat)), bcsub(bcmul($p2, cos(bcmul(3, $lat))), bcmul($p3, cos(bcmul(5, $lat)))));
  }
  else {
    $length = $p1 * cos($lat) - $p2 * cos(3 * $lat) - $p3 * cos(5 * $lat);
  }

  // Reset BCMath scale.
  farm_map_reset_bcscale();

  // Return the length.
  return (string) $length;
}