ardupilot/libraries/AP_Math/polygon.cpp

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/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
* polygon.cpp
* Copyright (C) Andrew Tridgell 2011
*
* This file 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 3 of the License, or
* (at your option) any later version.
*
* This file 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, see <http://www.gnu.org/licenses/>.
*/
#include "AP_Math.h"
/*
* The point in polygon algorithm is based on:
* http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
*/
/*
* Polygon_outside(): test for a point in a polygon
* Input: P = a point,
* V[] = vertex points of a polygon V[n+1] with V[n]=V[0]
* Return: true if P is outside the polygon
*
* This does not take account of the curvature of the earth, but we
* expect that to be very small over the distances involved in the
* fence boundary
*/
template <typename T>
bool Polygon_outside(const Vector2<T> &P, const Vector2<T> *V, unsigned n)
{
unsigned i, j;
bool outside = true;
for (i = 0, j = n-1; i < n; j = i++) {
if ((V[i].y > P.y) == (V[j].y > P.y)) {
continue;
}
int32_t dx1, dx2, dy1, dy2;
dx1 = P.x - V[i].x;
dx2 = V[j].x - V[i].x;
dy1 = P.y - V[i].y;
dy2 = V[j].y - V[i].y;
int8_t dx1s, dx2s, dy1s, dy2s, m1, m2;
#define sign(x) ((x)<0 ? -1 : 1)
dx1s = sign(dx1);
dx2s = sign(dx2);
dy1s = sign(dy1);
dy2s = sign(dy2);
m1 = dx1s * dy2s;
m2 = dx2s * dy1s;
2011-12-21 00:31:47 -04:00
// we avoid the 64 bit multiplies if we can based on sign checks.
if (dy2 < 0) {
if (m1 > m2) {
outside = !outside;
} else if (m1 < m2) {
continue;
} else if ( dx1 * (int64_t)dy2 > dx2 * (int64_t)dy1 ) {
outside = !outside;
}
} else {
if (m1 < m2) {
outside = !outside;
} else if (m1 > m2) {
continue;
} else if ( dx1 * (int64_t)dy2 < dx2 * (int64_t)dy1 ) {
outside = !outside;
}
}
}
return outside;
}
/*
* check if a polygon is complete.
*
* We consider a polygon to be complete if we have at least 4 points,
* and the first point is the same as the last point. That is the
* minimum requirement for the Polygon_outside function to work
*/
template <typename T>
bool Polygon_complete(const Vector2<T> *V, unsigned n)
{
return (n >= 4 && V[n-1].x == V[0].x && V[n-1].y == V[0].y);
}
// Necessary to avoid linker errors
template bool Polygon_outside<int32_t>(const Vector2l &P, const Vector2l *V, unsigned n);
template bool Polygon_complete<int32_t>(const Vector2l *V, unsigned n);
template bool Polygon_outside<float>(const Vector2f &P, const Vector2f *V, unsigned n);
template bool Polygon_complete<float>(const Vector2f *V, unsigned n);