kml/engine/bbox.h

// Copyright 2008, Google Inc. All rights reserved.
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// This file contains the definition of the Bbox class.

#ifndef KML_ENGINE_BBOX_H__
#define KML_ENGINE_BBOX_H__

namespace kmlengine {

const double kMinLat = -180.0;
const double kMaxLat = 180.0;
const double kMinLon = -180.0;
const double kMaxLon = 180.0;

// This class maintains a simple geographic bounding box.  Example usage:
//   Bbox bbox;
//   bbox.ExpandLatLon(lat, lon);  // 0 or more times for a set of lat,lon.
//
//   // Inquire some things about the bounding box:
//   double mid_lat, mid_lon;
//   bbox.GetCenter(&mid_lat, &mid_lon);
//   double north = bbox.get_north()  // Same for s,e,w
//   bool contains = bbox.Contains(lat, lon);
//
// NOTE: There is no provision for the ante-meridian nor for the validity
// of any latitude or longitude value.
class Bbox {
 public:
  // Construct a default bounding box.  The mininums and maximums are set such
  // that any valid latitude/longitude are handled properly.
  Bbox() : north_(kMinLat), south_(kMaxLat), east_(kMinLon), west_(kMaxLon) {}

  // Construct a bounding box of a given extent.  There are no checks for
  // the validity of these parameters.
  Bbox(double north, double south, double east, double west)
     : north_(north), south_(south), east_(east), west_(west) {}

  // This aligns this Bbox within the quadtree specified down to the maximum
  // level specified.
  void AlignBbox(Bbox* qt, unsigned int max_depth) {
    if (!qt) {
      return;
    }
    double lat = qt->GetCenterLat();
    double lon = qt->GetCenterLon();
    if (ContainedByBox(qt->get_north(), lat, qt->get_east(), lon)) {
      qt->set_south(lat);
      qt->set_west(lon);
    } else if (ContainedByBox(qt->get_north(), lat, lon, qt->get_west())) {
      qt->set_south(lat);
      qt->set_east(lon);
    } else if (ContainedByBox(lat, qt->get_south(), qt->get_east(), lon)) {
      qt->set_north(lat);
      qt->set_west(lon);
    } else if (ContainedByBox(lat, qt->get_south(), lon, qt->get_west())) {
      qt->set_north(lat);
      qt->set_east(lon);
    } else {
      return;  // target not contained by any child quadrant of qt.
    }
    // Fall through from above and recurse.
    if (max_depth > 0) {
      AlignBbox(qt, max_depth - 1);
    }
  }

  // This returns true if this Bbox is contained by the given Bbox.
  bool ContainedByBbox(const Bbox& b) const {
    return ContainedByBox(b.get_north(), b.get_south(), b.get_east(),
                          b.get_west());
  }

  // This returns true of this Bbox is contained with the given bounds.
  bool ContainedByBox(double north, double south,
                      double east, double west) const {
    return north >= north_ && south <= south_ && east >= east_ && west <= west_;
  }

  // This returns true if the bbox contains the given latitude,longitude.
  bool Contains(double latitude, double longitude) const {
    return north_ >= latitude && south_ <= latitude &&
           east_ >= longitude && west_ <= longitude;
  }

  // This expands this Bbox to contain the given Bbox.
  void ExpandFromBbox(const Bbox& bbox) {
    ExpandLatitude(bbox.get_north());
    ExpandLatitude(bbox.get_south());
    ExpandLongitude(bbox.get_east());
    ExpandLongitude(bbox.get_west());
  }

  // This expands the bounding box to include the given latitude.
  void ExpandLatitude(double latitude) {
    if (latitude > north_) {
      north_ = latitude;
    }
    if (latitude < south_) {
      south_ = latitude;
    }
  }

  // This expands the bounding box to include the given longitude.
  void ExpandLongitude(double longitude) {
    if (longitude > east_) {
      east_ = longitude;
    }
    if (longitude < west_) {
      west_ = longitude;
    }
  }

  // This expands the bounding box to include the given latitude and longitude.
  void ExpandLatLon(double latitude, double longitude) {
    ExpandLatitude(latitude);
    ExpandLongitude(longitude);
  }

  double get_north() const {
    return north_;
  }
  double get_south() const {
    return south_;
  }
  double get_east() const {
    return east_;
  }
  double get_west() const {
    return west_;
  }

  // This returns the center of the bounding box.
  void GetCenter(double* latitude, double* longitude) const {
    if (latitude) {
      *latitude = GetCenterLat();
    }
    if (longitude) {
      *longitude = GetCenterLon();
    }
  }

  double GetCenterLat() const {
    return (north_ + south_)/2.0;
  }

  double GetCenterLon() const {
    return (east_ + west_)/2.0;
  }

  void set_north(double n) {
    north_ = n;
  }
  void set_south(double s) {
    south_ = s;
  }
  void set_east(double e) {
    east_ = e;
  }
  void set_west(double w) {
    west_ = w;
  }

 private:
  double north_, south_, east_, west_;
};

}  // end namespace kmlengine

#endif  // KML_ENGINE_BBOX_H__