已知圆上三点,求圆心坐标,用qt
时间: 2023-07-12 16:21:53 浏览: 140
要求解圆心坐标,需要知道圆的方程,因此我们需要先求出圆的方程,然后再求解圆心坐标。
假设已知圆上三点为 (x1, y1), (x2, y2), (x3, y3),则圆的方程可以表示为:
```
(x - a)^2 + (y - b)^2 = r^2
```
其中,(a, b)为圆心坐标,r为圆的半径。将三个点带入上述方程,可以得到一个关于a, b, r的方程组,可以通过解方程组求解圆心坐标。
为了方便起见,我们可以先将方程转化为以下形式:
```
x^2 + y^2 + Ax + By + C = 0
```
其中,
```
A = -2a
B = -2b
C = a^2 + b^2 - r^2
```
将三个点带入上述方程,可以得到三个方程:
```
x1^2 + y1^2 + Ax1 + By1 + C = 0
x2^2 + y2^2 + Ax2 + By2 + C = 0
x3^2 + y3^2 + Ax3 + By3 + C = 0
```
将其写成矩阵形式:
```
| x1^2 + y1^2 x1 y1 1 | | A | | -C |
| x2^2 + y2^2 x2 y2 1 | * | B | = | -C |
| x3^2 + y3^2 x3 y3 1 | | C | | -C |
```
可以通过求解上述线性方程组得到A、B、C的值,从而求解圆心坐标和半径。
在Qt中可以使用QMatrix类来表示矩阵,使用QVector类来表示向量,可以通过QMatrix::inverted()函数求解矩阵的逆矩阵,进而求解线性方程组。具体实现如下:
```cpp
#include <QCoreApplication>
#include <QVector>
#include <QMatrix>
#include <QDebug>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
// 已知圆上三个点
double x1 = 0, y1 = 0;
double x2 = 1, y2 = 1;
double x3 = 2, y3 = 0;
// 构造系数矩阵
QMatrix A;
A(0, 0) = x1 * x1 + y1 * y1; A(0, 1) = x1; A(0, 2) = y1; A(0, 3) = 1;
A(1, 0) = x2 * x2 + y2 * y2; A(1, 1) = x2; A(1, 2) = y2; A(1, 3) = 1;
A(2, 0) = x3 * x3 + y3 * y3; A(2, 1) = x3; A(2, 2) = y3; A(2, 3) = 1;
A(3, 0) = 2 * x1; A(3, 1) = 1; A(3, 2) = 0; A(3, 3) = 0;
A(4, 0) = 2 * x2; A(4, 1) = 1; A(4, 2) = 0; A(4, 3) = 0;
A(5, 0) = 2 * x3; A(5, 1) = 1; A(5, 2) = 0; A(5, 3) = 0;
A(6, 0) = 0; A(6, 1) = 0; A(6, 2) = 2 * y1; A(6, 3) = 1;
A(7, 0) = 0; A(7, 1) = 0; A(7, 2) = 2 * y2; A(7, 3) = 1;
A(8, 0) = 0; A(8, 1) = 0; A(8, 2) = 2 * y3; A(8, 3) = 1;
// 构造常数向量
QVector<double> b(9);
b[0] = -x1 * x1 - y1 * y1;
b[1] = -x2 * x2 - y2 * y2;
b[2] = -x3 * x3 - y3 * y3;
b[3] = -2 * x1;
b[4] = -2 * x2;
b[5] = -2 * x3;
b[6] = -2 * y1;
b[7] = -2 * y2;
b[8] = -2 * y3;
// 求解线性方程组
QMatrix A_inv = A.inverted();
QVector<double> x = A_inv * b;
// 提取圆心坐标和半径
double a = -x[1] / 2;
double b = -x[2] / 2;
double r = sqrt(a * a + b * b - x[0]);
qDebug() << "圆心坐标:" << a << "," << b;
qDebug() << "半径:" << r;
return a.exec();
}
```
注意,这里的求解方法只适用于三个点不共线的情况,如果三个点共线,则无法构造出圆的方程。