/**
  * Return the smallest rectangle containing the intersection of this rectangle
  * and the given rectangle. Note that the region of intersection may consist
  * of two disjoint rectangles, in which case a single rectangle spanning both
  * of them is returned.
  *#/
  * public S2LatLngRect intersection(S2LatLngRect other) {
  * R1Interval intersectLat = lat.intersection(other.lat);
  * S1Interval intersectLng = lng.intersection(other.lng);
  * if (intersectLat.isEmpty() || intersectLng.isEmpty()) {
  * // The lat/lng ranges must either be both empty or both non-empty.
  * return empty();
  * }
  * return new S2LatLngRect(intersectLat, intersectLng);
  * }
  *
  * /**
  * Return a rectangle that contains the convolution of this rectangle with a
  * cap of the given angle. This expands the rectangle by a fixed distance (as
  * opposed to growing the rectangle in latitude-longitude space). The returned
  * rectangle includes all points whose minimum distance to the original
  * rectangle is at most the given angle.
  *#/
  * public S2LatLngRect convolveWithCap(S1Angle angle) {
  * // The most straightforward approach is to build a cap centered on each
  * // vertex and take the union of all the bounding rectangles (including the
  * // original rectangle; this is necessary for very large rectangles).
  *
  * // Optimization: convert the angle to a height exactly once.
  * S2Cap cap = S2Cap.fromAxisAngle(new S2Point(1, 0, 0), angle);
  *
  * S2LatLngRect r = this;
  * for (int k = 0; k < 4; ++k) {
  * S2Cap vertexCap = S2Cap.fromAxisHeight(getVertex(k).toPoint(), cap
  * .height());
  * r = r.union(vertexCap.getRectBound());
  * }
  * return r;
  * }
  *
  * /** Return the surface area of this rectangle on the unit sphere. *#/
  * public double area() {
  * if (isEmpty()) {
  * return 0;
  * }
  *
  * // This is the size difference of the two spherical caps, multiplied by
  * // the longitude ratio.
  * return lng().getLength() * Math.abs(Math.sin(latHi().radians()) - Math.sin(latLo().radians()));
  * }
  *
  * /** Return true if two rectangles contains the same set of points. *#/
  * @Override
  * public boolean equals(Object that) {
  * if (!(that instanceof S2LatLngRect)) {
  * return false;
  * }
  * S2LatLngRect otherRect = (S2LatLngRect) that;
  * return lat().equals(otherRect.lat()) && lng().equals(otherRect.lng());
  * }
  *
  * /**
  * Return true if the latitude and longitude intervals of the two rectangles
  * are the same up to the given tolerance (see r1interval.h and s1interval.h
  * for details).
  *#/
  * public boolean approxEquals(S2LatLngRect other, double maxError) {
  * return (lat.approxEquals(other.lat, maxError) && lng.approxEquals(
  * other.lng, maxError));
  * }
  *
  * public boolean approxEquals(S2LatLngRect other) {
  * return approxEquals(other, 1e-15);
  * }
  *
  * @Override
  * public int hashCode() {
  * int value = 17;
  * value = 37 * value + lat.hashCode();
  * return (37 * value + lng.hashCode());
  * }
  *
  * // //////////////////////////////////////////////////////////////////////
  * // S2Region interface (see {@code S2Region} for details):
  *
  * @Override
  * public S2Region clone() {
  * return new S2LatLngRect(this.lo(), this.hi());
  * }
  */
 public function getCapBound()
 {
     // We consider two possible bounding caps, one whose axis passes
     // through the center of the lat-long rectangle and one whose axis
     // is the north or south pole. We return the smaller of the two caps.
     if ($this->isEmpty()) {
         echo __METHOD__ . " empty\n";
         return S2Cap::sempty();
     }
     $poleZ = null;
     $poleAngle = null;
     if ($this->lat->lo() + $this->lat->hi() < 0) {
         // South pole axis yields smaller cap.
         $poleZ = -1;
         $poleAngle = S2::M_PI_2 + $this->lat->hi();
     } else {
         $poleZ = 1;
         $poleAngle = S2::M_PI_2 - $this->lat->lo();
     }
     $poleCap = S2Cap::fromAxisAngle(new S2Point(0, 0, $poleZ), S1Angle::sradians($poleAngle));
     // For bounding rectangles that span 180 degrees or less in longitude, the
     // maximum cap size is achieved at one of the rectangle vertices. For
     // rectangles that are larger than 180 degrees, we punt and always return a
     // bounding cap centered at one of the two poles.
     $lngSpan = $this->lng->hi() - $this->lng->lo();
     if (S2::IEEEremainder($lngSpan, 2 * S2::M_PI) >= 0) {
         if ($lngSpan < 2 * S2::M_PI) {
             $midCap = S2Cap::fromAxisAngle($this->getCenter()->toPoint(), S1Angle::sradians(0));
             for ($k = 0; $k < 4; ++$k) {
                 $midCap = $midCap->addPoint($this->getVertex($k)->toPoint());
             }
             if ($midCap->height() < $poleCap->height()) {
                 return $midCap;
             }
         }
     }
     return $poleCap;
 }
 /**
  * Return the distance (measured along the surface of the sphere) to the given
  * point.
  */
 public function getDistance(S2LatLng $o)
 {
     // This implements the Haversine formula, which is numerically stable for
     // small distances but only gets about 8 digits of precision for very large
     // distances (e.g. antipodal points). Note that 8 digits is still accurate
     // to within about 10cm for a sphere the size of the Earth.
     //
     // This could be fixed with another sin() and cos() below, but at that point
     // you might as well just convert both arguments to S2Points and compute the
     // distance that way (which gives about 15 digits of accuracy for all
     // distances).
     $lat1 = self::lat()->radians();
     $lat2 = $o->lat()->radians();
     $lng1 = self::lng()->radians();
     $lng2 = $o->lng()->radians();
     $dlat = sin(0.5 * ($lat2 - $lat1));
     $dlng = sin(0.5 * ($lng2 - $lng1));
     $x = $dlat * $dlat + $dlng * $dlng * cos($lat1) * cos($lat2);
     return S1Angle::sradians(2 * atan2(sqrt($x), sqrt(max(0.0, 1.0 - $x))));
     // Return the distance (measured along the surface of the sphere) to the
     // given S2LatLng. This is mathematically equivalent to:
     //
     // S1Angle::FromRadians(ToPoint().Angle(o.ToPoint())
     //
     // but this implementation is slightly more efficient.
 }
 /** Returns the longitude of this point as a new S1Angle. */
 public function lng()
 {
     return S1Angle::sradians($this->lngRadians);
 }
 /**
  * Return the cap opening angle in radians, or a negative number for empty
  * caps.
  */
 public function angle()
 {
     // This could also be computed as acos(1 - height_), but the following
     // formula is much more accurate when the cap height is small. It
     // follows from the relationship h = 1 - cos(theta) = 2 sin^2(theta/2).
     if ($this->isEmpty()) {
         return S1Angle::sradians(-1);
     }
     return S1Angle::sradians(2 * asin(sqrt(0.5 * $this->height)));
 }