230 lines
7.5 KiB
C++
230 lines
7.5 KiB
C++
/**
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* \file PolygonArea.cpp
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* \brief Implementation for GeographicLib::PolygonAreaT class
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*
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* Copyright (c) Charles Karney (2010-2022) <charles@karney.com> and licensed
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* under the MIT/X11 License. For more information, see
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* https://geographiclib.sourceforge.io/
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**********************************************************************/
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#include <GeographicLib/PolygonArea.hpp>
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#if defined(_MSC_VER)
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// Squelch warnings about enum-float expressions
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# pragma warning (disable: 5055)
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#endif
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namespace GeographicLib {
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using namespace std;
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template<class GeodType>
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int PolygonAreaT<GeodType>::transit(real lon1, real lon2) {
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// Return 1 or -1 if crossing prime meridian in east or west direction.
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// Otherwise return zero. longitude = +/-0 considered to be positive.
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// This is (should be?) compatible with transitdirect which computes
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// exactly the parity of
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// int(floor((lon1 + lon12) / 360)) - int(floor(lon1 / 360)))
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real lon12 = Math::AngDiff(lon1, lon2);
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lon1 = Math::AngNormalize(lon1);
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lon2 = Math::AngNormalize(lon2);
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// N.B. lon12 == 0 gives cross = 0
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return
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// edge case lon1 = 180, lon2 = 360->0, lon12 = 180 to give 1
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lon12 > 0 && ((lon1 < 0 && lon2 >= 0) ||
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// lon12 > 0 && lon1 > 0 && lon2 == 0 implies lon1 == 180
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(lon1 > 0 && lon2 == 0)) ? 1 :
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// non edge case lon1 = -180, lon2 = -360->-0, lon12 = -180
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(lon12 < 0 && lon1 >= 0 && lon2 < 0 ? -1 : 0);
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// This was the old method (treating +/- 0 as negative). However, with the
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// new scheme for handling longitude differences this fails on:
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// lon1 = -180, lon2 = -360->-0, lon12 = -180 gives 0 not -1.
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// return
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// lon1 <= 0 && lon2 > 0 && lon12 > 0 ? 1 :
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// (lon2 <= 0 && lon1 > 0 && lon12 < 0 ? -1 : 0);
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}
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// an alternate version of transit to deal with longitudes in the direct
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// problem.
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template<class GeodType>
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int PolygonAreaT<GeodType>::transitdirect(real lon1, real lon2) {
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// Compute exactly the parity of
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// int(floor(lon2 / 360)) - int(floor(lon1 / 360))
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using std::remainder;
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// C++ C remainder -> [-360, 360]
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// Java % -> (-720, 720) switch to IEEEremainder -> [-360, 360]
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// JS % -> (-720, 720)
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// Python fmod -> (-720, 720) swith to Math.remainder
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// Fortran, Octave skip
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// If mod function gives result in [-360, 360]
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// [0, 360) -> 0; [-360, 0) or 360 -> 1
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// If mod function gives result in (-720, 720)
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// [0, 360) or [-inf, -360) -> 0; [-360, 0) or [360, inf) -> 1
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lon1 = remainder(lon1, real(2 * Math::td));
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lon2 = remainder(lon2, real(2 * Math::td));
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return ( (lon2 >= 0 && lon2 < Math::td ? 0 : 1) -
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(lon1 >= 0 && lon1 < Math::td ? 0 : 1) );
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}
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template<class GeodType>
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void PolygonAreaT<GeodType>::AddPoint(real lat, real lon) {
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if (_num == 0) {
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_lat0 = _lat1 = lat;
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_lon0 = _lon1 = lon;
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} else {
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real s12, S12, t;
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_earth.GenInverse(_lat1, _lon1, lat, lon, _mask,
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s12, t, t, t, t, t, S12);
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_perimetersum += s12;
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if (!_polyline) {
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_areasum += S12;
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_crossings += transit(_lon1, lon);
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}
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_lat1 = lat; _lon1 = lon;
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}
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++_num;
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}
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template<class GeodType>
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void PolygonAreaT<GeodType>::AddEdge(real azi, real s) {
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if (_num) { // Do nothing if _num is zero
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real lat, lon, S12, t;
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_earth.GenDirect(_lat1, _lon1, azi, false, s, _mask,
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lat, lon, t, t, t, t, t, S12);
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_perimetersum += s;
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if (!_polyline) {
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_areasum += S12;
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_crossings += transitdirect(_lon1, lon);
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}
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_lat1 = lat; _lon1 = lon;
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++_num;
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}
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}
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template<class GeodType>
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unsigned PolygonAreaT<GeodType>::Compute(bool reverse, bool sign,
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real& perimeter, real& area) const
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{
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real s12, S12, t;
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if (_num < 2) {
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perimeter = 0;
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if (!_polyline)
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area = 0;
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return _num;
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}
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if (_polyline) {
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perimeter = _perimetersum();
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return _num;
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}
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_earth.GenInverse(_lat1, _lon1, _lat0, _lon0, _mask,
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s12, t, t, t, t, t, S12);
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perimeter = _perimetersum(s12);
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Accumulator<> tempsum(_areasum);
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tempsum += S12;
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int crossings = _crossings + transit(_lon1, _lon0);
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AreaReduce(tempsum, crossings, reverse, sign);
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area = real(0) + tempsum();
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return _num;
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}
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template<class GeodType>
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unsigned PolygonAreaT<GeodType>::TestPoint(real lat, real lon,
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bool reverse, bool sign,
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real& perimeter, real& area) const
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{
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if (_num == 0) {
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perimeter = 0;
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if (!_polyline)
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area = 0;
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return 1;
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}
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perimeter = _perimetersum();
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real tempsum = _polyline ? 0 : _areasum();
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int crossings = _crossings;
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unsigned num = _num + 1;
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for (int i = 0; i < (_polyline ? 1 : 2); ++i) {
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real s12, S12, t;
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_earth.GenInverse(i == 0 ? _lat1 : lat, i == 0 ? _lon1 : lon,
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i != 0 ? _lat0 : lat, i != 0 ? _lon0 : lon,
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_mask, s12, t, t, t, t, t, S12);
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perimeter += s12;
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if (!_polyline) {
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tempsum += S12;
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crossings += transit(i == 0 ? _lon1 : lon,
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i != 0 ? _lon0 : lon);
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}
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}
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if (_polyline)
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return num;
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AreaReduce(tempsum, crossings, reverse, sign);
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area = real(0) + tempsum;
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return num;
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}
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template<class GeodType>
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unsigned PolygonAreaT<GeodType>::TestEdge(real azi, real s,
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bool reverse, bool sign,
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real& perimeter, real& area) const
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{
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if (_num == 0) { // we don't have a starting point!
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perimeter = Math::NaN();
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if (!_polyline)
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area = Math::NaN();
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return 0;
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}
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unsigned num = _num + 1;
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perimeter = _perimetersum() + s;
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if (_polyline)
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return num;
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real tempsum = _areasum();
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int crossings = _crossings;
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{
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real lat, lon, s12, S12, t;
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_earth.GenDirect(_lat1, _lon1, azi, false, s, _mask,
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lat, lon, t, t, t, t, t, S12);
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tempsum += S12;
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crossings += transitdirect(_lon1, lon);
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_earth.GenInverse(lat, lon, _lat0, _lon0, _mask,
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s12, t, t, t, t, t, S12);
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perimeter += s12;
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tempsum += S12;
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crossings += transit(lon, _lon0);
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}
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AreaReduce(tempsum, crossings, reverse, sign);
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area = real(0) + tempsum;
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return num;
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}
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template<class GeodType>
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template<typename T>
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void PolygonAreaT<GeodType>::AreaReduce(T& area, int crossings,
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bool reverse, bool sign) const {
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Remainder(area);
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if (crossings & 1) area += (area < 0 ? 1 : -1) * _area0/2;
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// area is with the clockwise sense. If !reverse convert to
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// counter-clockwise convention.
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if (!reverse) area *= -1;
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// If sign put area in (-_area0/2, _area0/2], else put area in [0, _area0)
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if (sign) {
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if (area > _area0/2)
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area -= _area0;
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else if (area <= -_area0/2)
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area += _area0;
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} else {
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if (area >= _area0)
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area -= _area0;
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else if (area < 0)
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area += _area0;
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}
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}
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template class GEOGRAPHICLIB_EXPORT PolygonAreaT<Geodesic>;
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template class GEOGRAPHICLIB_EXPORT PolygonAreaT<GeodesicExact>;
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template class GEOGRAPHICLIB_EXPORT PolygonAreaT<Rhumb>;
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} // namespace GeographicLib
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