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/** @file latlong_metrics.cc
* @brief Geospatial distance metrics.
*/
/* Copyright 2008 Lemur Consulting Ltd
* Copyright 2011 Richard Boulton
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
* USA
*/
#include <config.h>
#include "xapian/geospatial.h"
#include "xapian/error.h"
#include "serialise-double.h"
#include <cmath>
using namespace Xapian;
using namespace std;
/** Quadratic mean radius of the Earth in metres.
*/
#define QUAD_EARTH_RADIUS_METRES 6372797.6
/** Set M_PI if it's not already set.
*/
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
LatLongMetric::~LatLongMetric()
{
}
double
LatLongMetric::operator()(const LatLongCoords & a,
const LatLongCoords &b) const
{
if (a.empty() || b.empty()) {
throw InvalidArgumentError("Empty coordinate list supplied to LatLongMetric::operator()().");
}
double min_dist = 0.0;
bool have_min = false;
for (LatLongCoordsIterator a_iter = a.begin();
a_iter != a.end();
++a_iter)
{
for (LatLongCoordsIterator b_iter = b.begin();
b_iter != b.end();
++b_iter)
{
double dist = pointwise_distance(*a_iter, *b_iter);
if (!have_min) {
min_dist = dist;
have_min = true;
} else if (dist < min_dist) {
min_dist = dist;
}
}
}
return min_dist;
}
double
LatLongMetric::operator()(const LatLongCoords & a,
const char * b_ptr, size_t b_len) const
{
if (a.empty() || b_len == 0) {
throw InvalidArgumentError("Empty coordinate list supplied to LatLongMetric::operator()().");
}
double min_dist = 0.0;
bool have_min = false;
LatLongCoord b;
const char * b_end = b_ptr + b_len;
while (b_ptr != b_end) {
b.unserialise(&b_ptr, b_end);
for (LatLongCoordsIterator a_iter = a.begin();
a_iter != a.end();
++a_iter)
{
double dist = pointwise_distance(*a_iter, b);
if (!have_min) {
min_dist = dist;
have_min = true;
} else if (dist < min_dist) {
min_dist = dist;
}
}
}
return min_dist;
}
GreatCircleMetric::GreatCircleMetric()
: radius(QUAD_EARTH_RADIUS_METRES)
{}
GreatCircleMetric::GreatCircleMetric(double radius_)
: radius(radius_)
{}
double
GreatCircleMetric::pointwise_distance(const LatLongCoord & a,
const LatLongCoord & b) const
{
double lata = a.latitude * (M_PI / 180.0);
double latb = b.latitude * (M_PI / 180.0);
double latdiff = lata - latb;
double longdiff = (a.longitude - b.longitude) * (M_PI / 180.0);
double sin_half_lat = sin(latdiff / 2);
double sin_half_long = sin(longdiff / 2);
double h = sin_half_lat * sin_half_lat +
sin_half_long * sin_half_long * cos(lata) * cos(latb);
if (rare(h > 1.0)) {
// Clamp to 1.0, asin(1.0) = M_PI / 2.0.
return radius * M_PI;
}
return 2 * radius * asin(sqrt(h));
}
LatLongMetric *
GreatCircleMetric::clone() const
{
return new GreatCircleMetric(radius);
}
string
GreatCircleMetric::name() const
{
return "Xapian::GreatCircleMetric";
}
string
GreatCircleMetric::serialise() const
{
return serialise_double(radius);
}
LatLongMetric *
GreatCircleMetric::unserialise(const string & s) const
{
const char * p = s.data();
const char * end = p + s.size();
double new_radius = unserialise_double(&p, end);
if (p != end) {
throw Xapian::NetworkError("Bad serialised GreatCircleMetric - junk at end");
}
return new GreatCircleMetric(new_radius);
}
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