Rotate method

[mstenta]

Feature request: add a rotate() method to the Geometry class that allows geometries to be rotated by a given angle around their centroid point.

[mstenta]

Here are two functions I wrote (outside of GeoPHP) for rotating a point and a polygon around an origin point. I'm using these in my farm management software - but ultimately they should probably be included in GeoPHP as methods for each class. So we'll also need to write the code for LineStrings, Collections, etc.

Also note: these include BCMath code as well. See #114 and #115

/**
 * Rotate a polygon around an origin.
 *
 * @param $polygon
 *   A Polygon geometry object.
 * @param $origin
 *   An origin point to rotate around.
 * @param $angle
 *   The angle of rotation, in degrees.
 *
 * @return \Polygon
 *   Returns a Polygon geometry object that has been rotated around an origin.
 */
function rotate_polygon($polygon, $origin, $angle) {

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

  // Iterate through the polygon's points, and rotate each around the origin.
  $linestring = $polygon->components[0];
  $new_points = array();
  if (!empty($linestring->components)) {
    foreach ($linestring->components as $point) {
      $new_points[] = farm_crop_bed_former_rotate_point($point, $origin, $angle);
    }
  }

  // Return a new Polygon object.
  return new Polygon(array(new LineString($new_points)));
}

/**
 * Rotate a point around an origin.
 *
 * @param $point
 *   A Point geometry object.
 * @param $origin
 *   An origin point to rotate around.
 * @param $angle
 *   The angle of rotation, in degrees.
 *
 * @return \Point
 *   Returns a Point geometry object that has been rotated around an origin.
 */
function rotate_point($point, $origin, $angle) {

  // If $point and $origin are not points, or $angle is not an integer between
  // 0 and 359, bail.
  if ($point->geometryType() != 'Point' || $origin->geometryType() != 'Point' || $angle < 0 || $angle > 359) {
    return $point;
  }

  // Convert the angle to radians.
  $angle = deg2rad($angle);

  // Calculate the new rotated points.
  if (geoPHP::bcmathInstalled()) {
    $x = bcadd($origin->x(), bcsub(bcmul(bcsub($point->x(), $origin->x()), cos($angle)), bcmul(bcsub($point->y(), $origin->y()), sin($angle))));
    $y = bcadd($origin->y(), bcadd(bcmul(bcsub($point->x(), $origin->x()), sin($angle)), bcmul(bcsub($point->y(), $origin->y()), cos($angle))));
  }
  else {
    $x = $origin->x() + (($point->x() - $origin->x()) * cos($angle)) - (($point->y() - $origin->y()) * sin($angle));
    $y = $origin->y() + (($point->x() - $origin->x()) * sin($angle)) + (($point->y() - $origin->y()) * cos($angle));
  }

  // Return a new Point object.
  return new Point($x, $y);
}