我正在尝试找出为什么下面的代码在 boost 1.61 中按预期工作，但在 boost 1.67 中却不能按预期工作。
在boost 1.61中，输入多边形被正确组合并显示轮廓多边形。
在 boost 1.67 中，在没有更改代码的情况下，轮廓多边形是错误且不完整的。就好像它有缺失点一样。
添加输出图像以帮助解释。我还需要添加一个 #define BOOST_1_6_1，因为 boost 1.61 似乎不会自动添加该头文件。
如果您想查看输入多边形的外观，请取消注释 drawAllPolygons()。
有人可以帮忙吗？
#include <iostream>
#include <boost\geometry.hpp>
//#define BOOST_1_6_1
#ifdef BOOST_1_6_1
#include <boost/geometry/geometries/point_xy.hpp>
#endif
typedef boost::geometry::model::d2::point_xy<int> intPt;
typedef boost::geometry::model::polygon<intPt> polygon;
const int GRID_WIDTH = 220;
const int GRID_HEIGHT = 60;
bool canvas[GRID_WIDTH][GRID_HEIGHT];
std::vector<polygon> output;
std::vector<polygon> input;
void initCanvas()
{
for (unsigned int y = 0; y < GRID_HEIGHT; ++y)
{
for (unsigned int x = 0; x < GRID_WIDTH; ++x)
{
canvas[x][y] = false;
}
}
}
void drawGrid()
{
for (unsigned int y = 0; y < GRID_HEIGHT; ++y)
{
for (unsigned int x = 0; x < GRID_WIDTH; ++x)
{
if (canvas[x][y])
{
std::cout << "x";
}
else
{
std::cout << ".";
}
}
std::cout << std::endl;
}
}
polygon setupPolygon(const int startX, const int startY, const int width, const int height)
{
polygon polygon1;
int endX = startX + width;
int endY = startY + height;
for (int x = startX; x <= endX; ++x)
{
intPt pt(x, startY);
polygon1.outer().push_back(pt);
}
for (int y = startY; y <= endY; ++y)
{
intPt pt(endX, y);
polygon1.outer().push_back(pt);
}
for (int x = endX; x >= startX; --x)
{
intPt pt(x, endY);
polygon1.outer().push_back(pt);
}
for (int y = endY; y >= startY; --y)
{
intPt pt(startX, y);
polygon1.outer().push_back(pt);
}
return polygon1;
}
std::vector<polygon> combine(std::vector<polygon> input)
{
bool loop = true;
while (loop)
{
unsigned int before = input.size();
bool exit = false;
for (unsigned int i = 0; i < input.size() && !exit; ++i)
{
for (unsigned int j = i + 1; j < input.size() && !exit; ++j)
{
std::vector<polygon> output;
boost::geometry::correct(input[i]);
boost::geometry::correct(input[j]);
boost::geometry::union_(input[i], input[j], output);
if (i < j)
{
input.erase(input.begin() + j);
input.erase(input.begin() + i);
}
else
{
input.erase(input.begin() + i);
input.erase(input.begin() + j);
}
input.insert(input.begin(), output.begin(), output.end());
exit = true;
}
}
if (before == input.size())
{
loop = false;
}
}
return input;
}
void drawAllPolygons()
{
for (unsigned int i = 0; i < input.size(); ++i)
{
auto outer = input[i].outer();
for (unsigned int i = 0; i < outer.size(); ++i)
{
int x = outer[i].get<0>();
int y = outer[i].get<1>();
canvas[x][y] = true;
}
}
}
void drawCombinedPolygons()
{
for (unsigned int j = 0; j < output.size(); ++j)
{
auto outer = output[j].outer();
for (unsigned int i = 0; i < outer.size(); ++i)
{
int x = outer[i].get<0>();
int y = outer[i].get<1>();
canvas[x][y] = true;
}
}
}
int main()
{
initCanvas();
input.push_back(setupPolygon(40, 10, 50, 15));
input.push_back(setupPolygon(40, 20, 50, 15));
input.push_back(setupPolygon(50, 10, 50, 15));
input.push_back(setupPolygon(60, 30, 50, 15));
output = combine(input);
//drawAllPolygons();
drawCombinedPolygons();
drawGrid();
std::cin.get();
return 0;
}
最佳答案
Boost 1.61 显然没有进行所有可能的优化。
存在不少误解。
输入多边形(环)的方向错误。您可以使用
is_valid和Correct来帮助自己。下面的代码将显示它。明确创建的原始多边形包含许多冗余点。即使您只是将其中一个与自身“结合”，您也可以预期结果会得到简化:
polygon p = setupPolygon(40, 10, 50, 15); std::cout << "original: " << bg::wkt(p) << "\n"; multi_polygon simple; bg::union_(p, p, simple); std::cout << "self-union: " << bg::wkt(simple) << "\n";将打印
original: POLYGON((40 10,40 11,40 12,40 13,40 14,40 15,40 16,40 17,40 18,40 19,40 20,40 21,40 22,40 23,40 24,40 25,40 25,41 25,42 25,43 25,44 25,45 25,46 25,47 25,48 25,49 25,50 25,51 25,52 25,53 25,54 25,55 25,56 25,57 25,58 25,59 25,60 25,61 25,62 25,63 25,64 25,65 25,66 25,67 25,68 25,69 25,70 25,71 25,72 25,73 25,74 25,75 25,76 25,77 25,78 25,79 25,80 25,81 25,82 25,83 25,84 25,85 25,86 25,87 25,88 25,89 25,90 25,90 25,90 24,90 23,90 22,90 21,90 20,90 19,90 18,90 17,90 16,90 15,90 14,90 13,90 12,90 11,90 10,90 10,89 10,88 10,87 10,86 10,85 10,84 10,83 10,82 10,81 10,80 10,79 10,78 10,77 10,76 10,75 10,74 10,73 10,72 10,71 10,70 10,69 10,68 10,67 10,66 10,65 10,64 10,63 10,62 10,61 10,60 10,59 10,58 10,57 10,56 10,55 10,54 10,53 10,52 10,51 10,50 10,49 10,48 10,47 10,46 10,45 10,44 10,43 10,42 10,41 10,40 10)) self-union: MULTIPOLYGON(((90 25,90 10,40 10,40 25,90 25)))如您所见，结果将被简化为仅显示矩形的明显角点。然而，您的“绘图”代码依赖于存在的冗余点。
这就是为什么你最终会得到“参差不齐”的结果 - 似乎错过了一些点，只是因为你的绘图代码没有绘制任何线条。它只是绘制(角)点。
canvas尺寸已反转我认为您的
canvas索引一直在交换。我建议使用更明确的数据结构和(可选)边界检查来避免这种情况。
更改为使用 SVG
如果你改变代码来输出输入和输出的SVG，你会发现整个事情变得非常有意义。请注意，这也会注意纠正输入:
#include <iostream>
#include <fstream>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
namespace bg = boost::geometry;
typedef bg::model::d2::point_xy<int> intPt;
typedef bg::model::polygon<intPt> polygon;
typedef bg::model::multi_polygon<polygon> multi_polygon;
const int GRID_WIDTH = 220;
const int GRID_HEIGHT = 60;
std::array<std::array<bool, GRID_WIDTH>, GRID_HEIGHT> canvas;
void initCanvas() {
for (auto& row : canvas)
for (auto& cell : row)
cell = false;
}
void drawGrid() {
for (auto& row : canvas) {
for (auto& cell : row)
std::cout << (cell?"x":".");
std::cout << std::endl;
}
}
template <typename R> void valid(R& g) {
std::string reason;
while (!bg::is_valid(g, reason)) {
std::cout << "Not valid: " << reason << "\n";
bg::correct(g);
}
}
polygon setupPolygon(const int startX, const int startY, const int width, const int height) {
polygon::ring_type r;
int const endX = startX + width;
int const endY = startY + height;
for (int x = startX; x <= endX; ++x) r.emplace_back(x, startY);
for (int y = startY; y <= endY; ++y) r.emplace_back(endX, y);
for (int x = endX; x >= startX; --x) r.emplace_back(x, endY);
for (int y = endY; y >= startY; --y) r.emplace_back(startX, y);
valid(r);
return {r};
}
template <typename Polygons>
multi_polygon combine(Polygons const& input) {
if (input.empty()) return {};
//if (input.size()<2) return {input.front()};
multi_polygon out;
for (polygon const& i : input) {
multi_polygon tmp;
bg::union_(out, i, tmp);
out = tmp;
}
return out;
}
void draw(polygon const& p) {
for (auto& pt : p.outer())
canvas.at(pt.y()).at(pt.x()) = true;
}
void draw(multi_polygon const& mp) { for (auto& p : mp) draw(p); }
void draw(std::vector<polygon> const& mp) { for (auto& p : mp) draw(p); }
void writeSvg(multi_polygon const& g, std::string fname) {
std::ofstream svg(fname);
boost::geometry::svg_mapper<intPt> mapper(svg, 400, 400);
mapper.add(g);
mapper.map(g, "fill-opacity:0.5;fill:rgb(0,0,153);stroke:rgb(0,0,200);stroke-width:2");
}
void writeSvg(std::vector<polygon> const& g, std::string fname) {
std::ofstream svg(fname);
boost::geometry::svg_mapper<intPt> mapper(svg, 400, 400);
for (auto& p: g) {
mapper.add(p);
mapper.map(p, "fill-opacity:0.5;fill:rgb(153,0,0);stroke:rgb(200,0,0);stroke-width:2");
}
}
int main() {
std::vector<polygon> input { {
setupPolygon(40, 10, 50, 15),
setupPolygon(40, 20, 50, 15),
setupPolygon(50, 10, 50, 15),
setupPolygon(60, 30, 50, 15),
} };
for (auto& p : input)
valid(p);
auto output = combine(input);
initCanvas();
draw(input);
drawGrid();
initCanvas();
draw(output);
drawGrid();
writeSvg(input, "input.svg");
writeSvg(output, "output.svg");
}
打印
Not valid: Geometry has wrong orientation
Not valid: Geometry has wrong orientation
Not valid: Geometry has wrong orientation
Not valid: Geometry has wrong orientation
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........................................xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.......................................................................................................................
........................................x.........x.......................................x.........x.......................................................................................................................
........................................x.........x.......................................x.........x.......................................................................................................................
........................................x.........x.......................................x.........x.......................................................................................................................
[ snip ]
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和 input.svg:
和输出.svg:
关于c++ - Boost union 在 1.67 中不起作用，但在 1.61 中起作用。为什么？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/51466736/