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// Copyright 2005 Google Inc. All Rights Reserved.
#include "s2.h"
#include "base/logging.h"
#include "strings/stringprintf.h"
#include "s2latlng.h"
S2LatLng S2LatLng::Normalized() const {
// remainder(x, 2 * M_PI) reduces its argument to the range [-M_PI, M_PI]
// inclusive, which is what we want here.
return S2LatLng(max(-M_PI_2, min(M_PI_2, lat().radians())),
remainder(lng().radians(), 2 * M_PI));
}
S2Point S2LatLng::ToPoint() const {
DCHECK(is_valid());
// As of crosstool v14, gcc tries to calculate sin(phi), cos(phi),
// sin(theta), cos(theta) on the following section by two sincos()
// calls. However, for some inputs, sincos() returns significantly
// different values between AMD and Intel.
//
// As a temporary workaround, "volatile" is added to phi and theta
// to prohibit the compiler to use such sincos() call, because sin()
// and cos() don't seem to have the problem. See b/3088321 for
// details.
volatile double phi = lat().radians();
volatile double theta = lng().radians();
double cosphi = cos(phi);
return S2Point(cos(theta) * cosphi, sin(theta) * cosphi, sin(phi));
}
S2LatLng::S2LatLng(S2Point const& p)
: coords_(Latitude(p).radians(), Longitude(p).radians()) {
// The latitude and longitude are already normalized.
DCHECK(is_valid());
}
S1Angle S2LatLng::GetDistance(S2LatLng const& o) const {
// 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).
DCHECK(is_valid());
DCHECK(o.is_valid());
double lat1 = lat().radians();
double lat2 = o.lat().radians();
double lng1 = lng().radians();
double lng2 = o.lng().radians();
double dlat = sin(0.5 * (lat2 - lat1));
double dlng = sin(0.5 * (lng2 - lng1));
double x = dlat * dlat + dlng * dlng * cos(lat1) * cos(lat2);
return S1Angle::Radians(2 * atan2(sqrt(x), sqrt(max(0.0, 1.0 - x))));
}
string S2LatLng::ToStringInDegrees() const {
S2LatLng pt = Normalized();
return StringPrintf("%f,%f", pt.lat().degrees(), pt.lng().degrees());
}
void S2LatLng::ToStringInDegrees(string* s) const {
*s = ToStringInDegrees();
}
ostream& operator<<(ostream& os, S2LatLng const& ll) {
return os << "[" << ll.lat() << ", " << ll.lng() << "]";
}
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