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/**********************************************************************
*
* GEOS - Geometry Engine Open Source
* http://geos.osgeo.org
*
* Copyright (C) 2025 Martin Davis
*
* This is free software; you can redistribute and/or modify it under
* the terms of the GNU Lesser General Public Licence as published
* by the Free Software Foundation.
* See the COPYING file for more information.
*
**********************************************************************/
/*--------------------------------------------------------------
* Computes orientation index for a line segment and a point,
* in a grid of contiguous FP numbers around the point.
* Uses either DD (robust) or FP algorithms.
*
* Examples:
* orientview 0 0 1 1 0.5 0.5
* orientview 0 2 2 0 0.4 1.6
* orientview -g 0 2 2 0 0.4 1.6
* orientview -g -f -v 0 2 2 0 0.4 1.6
* orientview -p 9 0 0 9 8.6 0.4
-------------------------------------------------------------*/
#include <geos/algorithm/Orientation.h>
#include <geos/geom/Coordinate.h>
#include <geos/geom/CoordinateSequence.h>
#include <geos/geom/GeometryFactory.h>
#include <algorithm>
#include <random>
#include <vector>
#include <memory>
#include <iomanip>
using namespace geos::geom;
using geos::algorithm::Orientation;
bool isVerbose = false;
bool showGraph = false;
bool isFP = false;
bool isPermute = false;
double p0x, p0y, p1x, p1y, p2x, p2y;
void printUsage() {
std::cout << "GEOS Orientation Index Viewer" << std::endl;
std::cout << "Usage: orientview [ flags ] x0 y0 x1 y1 x2 y2" << std::endl;
std::cout << " -f - use FP instead of DD orientation algorithm" << std::endl;
std::cout << " -g - show grid of nearby points" << std::endl;
std::cout << " -p - compute all permutations of points" << std::endl;
std::cout << " -v - show verbose detail for each point" << std::endl;
std::cout << "Example: orientview -g -p 0 2 2 0 0.4 1.6" << std::endl;
}
void parseFlag(char* arg) {
char flag = arg[1];
switch (flag) {
case 'f':
isFP = true; break;
case 'g':
showGraph = true; break;
case 'p':
isPermute = true; break;
case 'v':
isVerbose = true; break;
}
}
void parseArgs(int argc, char** argv) {
int i = 1;
//-- parse flags
while (argv[i][0] == '-' && isalpha(argv[i][1])) {
parseFlag(argv[i]);
i++;
}
//-- parse points
if (argc - i < 6) {
std::cerr << "3 coordinates must be specified";
exit(EXIT_FAILURE);
}
// assert: there are 6 ordinates = 3 coordinates
p0x = std::stod(argv[i]);
p0y = std::stod(argv[i+1]);
p1x = std::stod(argv[i+2]);
p1y = std::stod(argv[i+3]);
p2x = std::stod(argv[i+4]);
p2y = std::stod(argv[i+5]);
}
int
orientationIndexFP(const Coordinate& p1, const Coordinate& p2,const Coordinate& q){
double dx1 = p2.x-p1.x;
double dy1 = p2.y-p1.y;
double dx2 = q.x-p2.x;
double dy2 = q.y-p2.y;
double det = dx1 * dy2 - dx2 * dy1;
if (det > 0.0) return 1;
if (det < 0.0) return-1;
return 0;
}
double nextafterN(double x, double dir, size_t n) {
for (size_t i = 0; i < n; i++) {
x = nextafter(x, dir);
}
return x;
}
void computePoint(size_t ix, size_t iy, double x, double y, Coordinate p0, Coordinate p1, bool useFP, bool showDetail)
{
Coordinate p(x, y);
int index;
if (useFP) {
index = orientationIndexFP(p0, p1, p);
}
else {
index = Orientation::index(p0, p1, p);
}
char c = '0';
if (index < 0) c = '-';
if (index > 0) c = '+';
std::cout << c;
(void)ix;
(void)iy;
if (showDetail) {
std::cout << " " << (useFP ? "FP" : "DD")
<< " [ " << ix << ", " << iy << " ] "
<< std::setprecision(20)
<< "POINT ( " << x << " " << y << " ) -> " << index << std::endl;
}
}
void computeGrid(double x0, double y0, double x1, double y1, double xp, double yp, size_t n) {
Coordinate p0(x0, y0);
Coordinate p1(x1, y1);
std::cout << std::setprecision(20) << "LINESTRING ( " << x0 << " " << y0 << ", " << x1 << " " << y1 << " )" << std::endl;
computePoint(0, 0, xp, yp, p0, p1, false, true);
computePoint(0, 0, xp, yp, p0, p1, true, true);
std::cout << std::endl;
if (showGraph) {
size_t nGrid = 2 * n + 1;
std::cout << (isFP ? "Orientation FP" : "Orientation DD") << std::endl;
//-- display grid limits
double xmin = nextafterN(xp, xp - 1, n);
double ymin = nextafterN(yp, xp - 1, n);
double xmax = nextafterN(xp, xp + 1, n);
double ymax = nextafterN(yp, yp + 1, n);
std::cout << "Grid: "
<< std::setprecision(20)
<< "(" << xmin << " " << ymin << " ) - "
<< "(" << xmax << " " << ymax << " )"
<< std::endl;
//-- display grid size for X and Y
double xdel = nextafter(xp, xp - 1) - xp;
double ydel = nextafter(yp, yp - 1) - yp;
std::cout << "Size: "
<< std::setprecision(20)
<< "dX = " << xdel << " dy = " << ydel
<< std::endl;
double y = nextafterN(yp, yp + 1, n);
for (size_t iy = nGrid; iy > 0; iy--) {
double x = nextafterN(xp, xp - 1, n);
for (size_t ix = 0; ix <= nGrid; ix++) {
computePoint(ix, iy, x, y, p0, p1, isFP, isVerbose);
x = nextafter(x, x + 1);
}
std::cout << std::endl;
y = nextafter(y, y - 1);
}
}
}
int main(int argc, char** argv) {
if (argc <= 1) {
printUsage();
exit(EXIT_SUCCESS);
}
parseArgs(argc, argv);
const int gridSize = 20;
computeGrid(p0x, p0y, p1x, p1y, p2x, p2y, gridSize);
if (isPermute) {
std::cout << std::endl;
computeGrid(p1x, p1y, p2x, p2y, p0x, p0y, gridSize);
std::cout << std::endl;
computeGrid(p2x, p2y, p0x, p0y, p1x, p1y, gridSize);
}
}
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