基于matlab mex的平面点集按重心逆时针排序算法

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基于matlab mex的平面点集按重心逆时针排序算法，可用于求凸集，代码如下：

#include <mex.h>
#include <mat.h>
#include <stdlib.h>
#include <vector>
#include <algorithm>

using namespace std;

typedef struct PointF {
    int id;
    double x, y;
    PointF() {
        id = -1;
    }
    PointF(int id, double x, double y) : id(id), x(x), y(y) {}
} PointF;

typedef vector<PointF> Points;

Points points;
PointF cpt;

bool compare(const PointF p1, const PointF p2) {
    //mexPrintf("%d %d\n", p1.id, p2.id);
    PointF a = p1, b = p2;
    int aid, bid;
    if (a.x >= cpt.x) {
        if (a.y <= cpt.y)
            aid = 1;
        else
            aid = 2;
    }
    if (a.x < cpt.x) {
        if (a.y >= cpt.y)
            aid = 3;
        else
            aid = 4;
    }
    if (b.x >= cpt.x) {
        if (b.y <= cpt.y)
            bid = 1;
        else
            bid = 2;
    }
    if (b.x < cpt.x) {
        if (b.y >= cpt.y)
            bid = 3;
        else
            bid = 4;
    }
    if (aid < bid)
        return true;
    else if (aid == bid) {
        if (aid == 1 || aid == 2)
            return a.y < b.y;
        if (aid == 3 || aid == 4)
            return a.y > b.y;
    }
    else
        return false;
}

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
    if (nrhs != 2) {
        mexPrintf("Usage: 2dsort(xy_nrows_2cols, refpoint_x_y).\n");
        return;
    }
    
    int ndim = mxGetNumberOfDimensions(prhs[0]);
    //mexPrintf("%d\n", ndim);
    const int *dims = mxGetDimensions( prhs[0] );
    //mexPrintf("%d %d dims\n", dims[0], dims[1]);
    if (dims[1] != 2) {
       mexPrintf("Error: input data should be with 2 columns.\n");
       return;
    }
    
    double *data = mxGetPr( prhs[0] );
    for(int i = 0; i < dims[0]; i++) {
        points.push_back(PointF(i + 1, data[i], data[i + dims[0]]));
        //mexPrintf("*%d ", points[i].id);
    }
    
    double *data1 = mxGetPr( prhs[1] );
    cpt.x = data1[0];
    cpt.y = data1[1];
    for(int i = 0; i < dims[0]; i++) {
        mexPrintf("%d ", points[i].id);
    }
    mexPrintf("\n");
    sort(points.begin(), points.end(), compare);
    for(int i = 0; i < dims[0]; i++) {
        mexPrintf("%d ", points[i].id);
    }
    mexPrintf("\n");
    
    nlhs = 1;
    plhs[0] = mxCreateDoubleMatrix(dims[0], 1, mxREAL);
    double *dest = mxGetPr( plhs[0] );
    for(int i = 0; i < dims[0]; i++)
        dest[i] = points[i].id;
}

测试代码：

close all;

mex twodsort.cpp;

N = 300;
xy = rand(N, 2);
ctr = sum(xy) ./ N;

plot(xy(:, 1), xy(:, 2), '*r');
hold on;
plot(ctr(1), ctr(2), '+b');

ids = twodsort(xy, ctr);
ids(end + 1) = ids(1);
plot(xy(ids(1), 1), xy(ids(1), 2), '.g', 'MarkerSize', 5);
for i = 1:N
    j = i + 1;
    if (j > N)
        j = 1;
    end;
    plot([xy(ids(i), 1); xy(ids(j), 1)], [xy(ids(i), 2); xy(ids(j), 2)], '-', 'Color', [i/(N+1), 0, 0], 'LineWidth', 2);
end;

基于matlab mex的平面点集按重心逆时针排序算法

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原文地址：http://blog.csdn.net/miscclp/article/details/44432541