function farm_map_polygon_area in farmOS 7

Calculate the area of a Polygon in square meters.

Parameters

Polygon $polygon: The polygon to measure.

Return value

string Returns the area of the polygon as a string, in square meters.

1 call to farm_map_polygon_area()

farm_area_calculate_area in modules/farm/farm_area/farm_area.module

Calculate the area of a farm area.

File

modules/farm/farm_map/farm_map.geo.inc, line 360

Farm map geometry functions.

Code

function farm_map_polygon_area($polygon) {

  // Load GeoPHP.
  geophp_load();

  // If the geometry is not a polygon, bail.
  if ($polygon
    ->geometryType() != 'Polygon' || $polygon->components[0]
    ->geometryType() != 'LineString') {
    return $polygon;
  }

  // Set BCMath scale.
  farm_map_set_bcscale();

  // We're going to do a pseudo-projection of the polygon into a coordinate
  // system that is measured in meters, and then run a standard area calculation
  // on that. We'll do this by first finding the bounding box of the polygon,
  // and use the lower left point as origin. Then, we'll calculate the latitude
  // and longitude lengths of the polygon's centroid point, and use those to
  // calculate the new point positions.
  // Get the bounding box of the polygon.
  $bbox = $polygon
    ->getBBox();

  // Create an origin point.
  $origin = new Point($bbox['minx'], $bbox['miny']);

  // Get the polygon's centroid point.
  $centroid = $polygon
    ->centroid();

  // Calculate the latitude/longitude degree lengths at the centroid point.
  $lon_deg_len = farm_map_lon_deg_len($centroid
    ->getY());
  $lat_deg_len = farm_map_lat_deg_len($centroid
    ->getY());

  // Iterate through the polygon's points and map them to new points.
  $line = $polygon->components[0];
  $new_points = array();
  foreach ($line
    ->getPoints() as $delta => $point) {

    // Calculate the distance between the point and origin.
    $distance_x = $point
      ->getX() - $origin
      ->getX();
    $distance_y = $point
      ->getY() - $origin
      ->getY();

    // Multiply distances by latitude/longitude degree lengths to get new point.
    $new_x = $distance_x * $lon_deg_len;
    $new_y = $distance_y * $lat_deg_len;

    // Add the new point.
    $new_points[] = new Point($new_x, $new_y);
  }

  // Construct a new polygon.
  $new_polygon = new Polygon(array(
    new LineString($new_points),
  ));

  // Calculate the area of the new polygon.
  $area = $new_polygon
    ->area();

  // Reset BCMath scale.
  farm_map_reset_bcscale();

  // Return the area as a string.
  return (string) $area;
}