c ++顺时针排序2D点 [英] c++ Sorting 2D Points clockwise
问题描述
我写了一个程序,从12点开始以顺时针方式在图形上排列点,这样,包含这些点的向量就按该顺序排序。我正在使用atan2从12点开始获取角度,然后根据象限进行调整。我试图找出错误的来源,因为它没有正确订购它们。因此,给定4个随机点(如照片中的随机点),它应该在包含矢量的顺序为P1,P2,P3,P4
这是我的代码:
i wrote a program to arrange points on a graph in clockwise manner from 12 o'clock such that, a vector containing these points is sorted in that order. I am using atan2 to get the angle from 12 o'clock and then making adjustments based on the quadrant. i am trying to figure out where the bug is coming from as it is not ordering them correctly. So given 4 random points like those in the photo, it should order then in the containing vector as P1,P2,P3,P4 Here is my code:
//sort_points.cpp
#include <iostream>
#include <math.h>
#include <algorithm>
#include <vector>
using namespace std;
class Point
{
public:
double x;
double y;
Point(double xx, double yy) : x(xx), y(yy) {}
~Point();
inline friend ostream& operator<<(ostream& output, const Point& point)
{
output << "[" << point.x << ", " << point.y <<"]";
return output;
}
};
Point::~Point() {;}
/* get quadrant from 12 o'clock*/
int get_quadrant (const Point& p)
{
int result = 4; //origin
if (p.x > 0 && p.y > 0)
return 1;
else if(p.x < 0 && p.y > 0)
return 2;
else if(p.x < 0 && p.y < 0)
return 3;
//else 4th quadrant
return result;
}
double get_clockwise_angle(const Point& p)
{
double angle = 0.0;
int quadrant = get_quadrant(p);
/*making sure the quadrants are correct*/
cout << "Point: " << p << " is on the " << quadrant << " quadrant" << endl;
/*add the appropriate pi/2 value based on the quadrant. (one of 0, pi/2, pi, 3pi/2)*/
switch(quadrant)
{
case 1:
angle = atan2(p.x,p.y) * 180/M_PI;
break;
case 2:
angle = atan2(p.y, p.x)* 180/M_PI;
angle += M_PI/2;
break;
case 3:
angle = atan2(p.x,p.y)* 180/M_PI;
angle += M_PI;
break;
case 4:
angle = atan2(p.y, p.x)* 180/M_PI;
angle += 3*M_PI/2;
break;
}
return angle;
}
bool compare_points(const Point& a, const Point& b)
{
return (get_clockwise_angle(a) < get_clockwise_angle(b));
}
int main(int argc, char const *argv[])
{
std::vector <Point> points;
points.push_back( Point( 1, 3 ) );
points.push_back( Point( 2, 1 ) );
points.push_back( Point( -3, 2 ) );
points.push_back( Point( -1, -1 ) );
cout << "\nBefore sorting" << endl;
for (int i = 0; i < points.size(); ++i)
{
cout << points.at(i) << endl;
}
std::sort(points.begin(), points.end(),compare_points);
cout << "\nAfter sorting" << endl;
for (int i = 0; i < points.size(); ++i)
{
cout << points.at(i) << endl;
}
return 0;
}
推荐答案
您不需要调整。 atan2
将为您提供x轴正方向的角度,即-PI到PI的逆时针方向。
You don't need the adjustment. atan2
will give you the angle from positive direction of x axis, counterclockwise in range of -PI to PI.
首先,要使起点为y轴正方向,让我将参数赋予 atan2
,就好像y轴的负方向为x轴的正方向和x的正方向一样
Firstly, to make the starting point positive direction of y axis, let me give parameter to atan2
as if negative direction of y axis is positive direction of x axis and positive direction of x axis is positive direction is y axis.
然后,这将使角度逆时针旋转,因此取反角度即可反转顺序。
Then, this will make the angle counterclockwise, so negate the angle in order to reverse the order.
double get_clockwise_angle(const Point& p)
{
double angle = 0.0;
int quadrant = get_quadrant(p);
/*making sure the quadrants are correct*/
cout << "Point: " << p << " is on the " << quadrant << " quadrant" << endl;
/*calculate angle and return it*/
angle = -atan2(p.x,-p.y);
return angle;
}
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