C++ 创建最小包围盒子
时间: 2024-01-04 19:58:35 浏览: 123
最小包围盒子(bounding box)是一种能够包围物体或几何形状的盒子,通常用于计算机图形学、物理模拟、碰撞检测等领域。创建最小包围盒子的方法主要有以下几种:
1. 基于几何形状的包围盒子:对于一些简单的几何形状,如球体、立方体等,可以直接创建其对应的包围盒子。
2. 基于顶点的包围盒子:对于复杂的几何模型,可以计算其所有顶点的最小和最大值,从而得到一个包围盒子。
3. 基于包围盒子的包围盒子:对于一组物体或几何形状,可以先创建一个包围所有物体的大包围盒子,再在其中创建每个物体的小包围盒子。
4. 基于分治的包围盒子:将一个物体或几何形状分成多个小部分,对每个小部分分别创建包围盒子,再将这些小包围盒子合并成一个大包围盒子。
在实际应用中,根据需要选择不同的方法创建最小包围盒子,以提高计算效率和精度。
相关问题
NX二次开发 通过OBB算法实现最小包围盒,C++实现
OBB(Oriented Bounding Box)算法是一种用于计算物体包围盒的算法,它可以将一个物体用一个最小的矩形盒子包围起来。下面是一个使用C++实现OBB算法的示例代码。
首先,我们需要定义一个表示3D向量的结构体:
```c++
struct Vector3
{
float x, y, z;
Vector3() : x(0), y(0), z(0) {}
Vector3(float x_, float y_, float z_) : x(x_), y(y_), z(z_) {}
Vector3 operator+(const Vector3& other) const
{
return Vector3(x + other.x, y + other.y, z + other.z);
}
Vector3 operator*(float scalar) const
{
return Vector3(x * scalar, y * scalar, z * scalar);
}
Vector3 operator-(const Vector3& other) const
{
return Vector3(x - other.x, y - other.y, z - other.z);
}
// 计算向量的长度
float Length() const
{
return sqrt(x * x + y * y + z * z);
}
// 计算向量的单位向量
Vector3 Normalized() const
{
float len = Length();
if (len > 0)
{
return Vector3(x / len, y / len, z / len);
}
else
{
return Vector3();
}
}
};
```
接下来,定义一个表示3D物体的结构体,包含物体的顶点和面信息:
```c++
struct Mesh
{
std::vector<Vector3> vertices;
std::vector<std::vector<int>> faces;
// 计算物体的最小包围盒
void CalculateOBB(Vector3& center, Vector3& size, Vector3& axisX, Vector3& axisY, Vector3& axisZ) const
{
// 计算物体的中心点
center = Vector3();
for (int i = 0; i < vertices.size(); i++)
{
center = center + vertices[i];
}
center = center * (1.0f / vertices.size());
// 计算协方差矩阵
float cov[3][3] = { 0 };
for (int i = 0; i < vertices.size(); i++)
{
Vector3 delta = vertices[i] - center;
cov[0][0] += delta.x * delta.x;
cov[0][1] += delta.x * delta.y;
cov[0][2] += delta.x * delta.z;
cov[1][0] += delta.y * delta.x;
cov[1][1] += delta.y * delta.y;
cov[1][2] += delta.y * delta.z;
cov[2][0] += delta.z * delta.x;
cov[2][1] += delta.z * delta.y;
cov[2][2] += delta.z * delta.z;
}
// 计算协方差矩阵的特征向量和特征值
float eigenvalues[3];
float eigenvectors[3][3];
diagonalize(cov, eigenvalues, eigenvectors);
// 计算物体的大小以及三个轴的方向
size = Vector3(sqrt(eigenvalues[0]), sqrt(eigenvalues[1]), sqrt(eigenvalues[2]));
axisX = Vector3(eigenvectors[0][0], eigenvectors[1][0], eigenvectors[2][0]);
axisY = Vector3(eigenvectors[0][1], eigenvectors[1][1], eigenvectors[2][1]);
axisZ = Vector3(eigenvectors[0][2], eigenvectors[1][2], eigenvectors[2][2]);
}
private:
void diagonalize(float mat[3][3], float eigenvalues[3], float eigenvectors[3][3]) const
{
// 采用Jacobi迭代法求解特征向量和特征值
constexpr int MAX_ITERATIONS = 100;
constexpr float EPSILON = 1e-8f;
float offdiag = 0.0f;
float maxOffdiag = 0.0f;
float diag[3] = { mat[0][0], mat[1][1], mat[2][2] };
float off[3] = { mat[1][2], mat[0][2], mat[0][1] };
float rot[3][3] = { 0 };
for (int i = 0; i < MAX_ITERATIONS; i++)
{
int p, q;
maxOffdiag = off[0];
p = 0;
q = 1;
if (fabsf(off[1]) > fabsf(maxOffdiag))
{
maxOffdiag = off[1];
p = 1;
q = 2;
}
if (fabsf(off[2]) > fabsf(maxOffdiag))
{
maxOffdiag = off[2];
p = 0;
q = 2;
}
if (fabsf(maxOffdiag) < EPSILON)
{
break;
}
float theta = (diag[q] - diag[p]) / (2.0f * maxOffdiag);
float s = (theta >= 0.0f) ? 1.0f : -1.0f;
float t = s / (fabsf(theta) + sqrt(1.0f + theta * theta));
float c = sqrt(1.0f - t * t);
float tau = t / (1.0f + c);
float tmp = s * maxOffdiag;
diag[p] -= tmp;
diag[q] += tmp;
off[p] -= tmp;
off[q] = 0.0f;
for (int j = 0; j < 3; j++)
{
tmp = c * rot[j][p] - s * rot[j][q];
rot[j][q] = s * rot[j][p] + c * rot[j][q];
rot[j][p] = tmp;
}
for (int j = 0; j < 3; j++)
{
tmp = c * rot[p][j] - s * rot[q][j];
rot[q][j] = s * rot[p][j] + c * rot[q][j];
rot[p][j] = tmp;
}
}
eigenvalues[0] = diag[0];
eigenvalues[1] = diag[1];
eigenvalues[2] = diag[2];
eigenvectors[0][0] = rot[0][0];
eigenvectors[0][1] = rot[0][1];
eigenvectors[0][2] = rot[0][2];
eigenvectors[1][0] = rot[1][0];
eigenvectors[1][1] = rot[1][1];
eigenvectors[1][2] = rot[1][2];
eigenvectors[2][0] = rot[2][0];
eigenvectors[2][1] = rot[2][1];
eigenvectors[2][2] = rot[2][2];
}
};
```
最后,我们可以通过以下代码来使用OBB算法计算物体的包围盒:
```c++
Mesh mesh;
// 加载物体的顶点和面信息
// ...
Vector3 center, size, axisX, axisY, axisZ;
mesh.CalculateOBB(center, size, axisX, axisY, axisZ);
```
这样,我们就可以获得物体的最小包围盒的中心点、大小以及三个轴的方向了。
NX二次开发,用C++ 写一个OBB算法来创建实体的最小包容盒
OBB(oriented bounding box)算法是一种用于计算三维物体包围盒的算法,它可以创建一个最小的、能够完全包含物体的矩形盒子。以下是使用C++语言编写OBB算法的基本步骤:
1. 定义点和向量结构体
```c++
struct Point {
float x, y, z;
};
struct Vector {
float x, y, z;
};
```
2. 计算物体的中心点
```c++
Point computeCenterPoint(Point* points, int numPoints) {
Point center = { 0.0f, 0.0f, 0.0f };
for (int i = 0; i < numPoints; i++) {
center.x += points[i].x;
center.y += points[i].y;
center.z += points[i].z;
}
center.x /= numPoints;
center.y /= numPoints;
center.z /= numPoints;
return center;
}
```
3. 计算物体的协方差矩阵
```c++
Matrix3x3 computeCovarianceMatrix(Point* points, int numPoints) {
Point center = computeCenterPoint(points, numPoints);
Matrix3x3 covarianceMatrix = { 0.0f };
for (int i = 0; i < numPoints; i++) {
Vector v = { points[i].x - center.x, points[i].y - center.y, points[i].z - center.z };
covarianceMatrix.m11 += v.x * v.x;
covarianceMatrix.m12 += v.x * v.y;
covarianceMatrix.m13 += v.x * v.z;
covarianceMatrix.m21 += v.y * v.x;
covarianceMatrix.m22 += v.y * v.y;
covarianceMatrix.m23 += v.y * v.z;
covarianceMatrix.m31 += v.z * v.x;
covarianceMatrix.m32 += v.z * v.y;
covarianceMatrix.m33 += v.z * v.z;
}
covarianceMatrix.m11 /= numPoints;
covarianceMatrix.m12 /= numPoints;
covarianceMatrix.m13 /= numPoints;
covarianceMatrix.m21 = covarianceMatrix.m12;
covarianceMatrix.m22 /= numPoints;
covarianceMatrix.m23 /= numPoints;
covarianceMatrix.m31 = covarianceMatrix.m13;
covarianceMatrix.m32 = covarianceMatrix.m23;
covarianceMatrix.m33 /= numPoints;
return covarianceMatrix;
}
```
4. 计算物体的主轴
```c++
void computePrincipalAxis(Matrix3x3 covarianceMatrix, Vector* axis) {
float eigenvalues[3];
Vector eigenvectors[3];
diagonalize(covarianceMatrix, eigenvalues, eigenvectors);
int maxEigenvalueIndex = 0;
float maxEigenvalue = eigenvalues[0];
for (int i = 1; i < 3; i++) {
if (eigenvalues[i] > maxEigenvalue) {
maxEigenvalueIndex = i;
maxEigenvalue = eigenvalues[i];
}
}
axis->x = eigenvectors[maxEigenvalueIndex].x;
axis->y = eigenvectors[maxEigenvalueIndex].y;
axis->z = eigenvectors[maxEigenvalueIndex].z;
}
```
5. 计算物体的OBB
```c++
void computeOBB(Point* points, int numPoints, Point* obbCenter, Vector* obbAxis, Vector* obbExtent) {
Matrix3x3 covarianceMatrix = computeCovarianceMatrix(points, numPoints);
computePrincipalAxis(covarianceMatrix, obbAxis);
Point center = computeCenterPoint(points, numPoints);
obbCenter->x = center.x + obbAxis->x * dotProduct(points[0], *obbAxis);
obbCenter->y = center.y + obbAxis->y * dotProduct(points[0], *obbAxis);
obbCenter->z = center.z + obbAxis->z * dotProduct(points[0], *obbAxis);
float minX, minY, minZ, maxX, maxY, maxZ;
minX = minY = minZ = FLT_MAX;
maxX = maxY = maxZ = -FLT_MAX;
for (int i = 0; i < numPoints; i++) {
Vector p = { points[i].x - obbCenter->x, points[i].y - obbCenter->y, points[i].z - obbCenter->z };
Vector e = { obbAxis->x * dotProduct(p, *obbAxis), obbAxis->y * dotProduct(p, *obbAxis), obbAxis->z * dotProduct(p, *obbAxis) };
if (e.x < minX) minX = e.x;
if (e.y < minY) minY = e.y;
if (e.z < minZ) minZ = e.z;
if (e.x > maxX) maxX = e.x;
if (e.y > maxY) maxY = e.y;
if (e.z > maxZ) maxZ = e.z;
}
obbExtent->x = (maxX - minX) * 0.5f;
obbExtent->y = (maxY - minY) * 0.5f;
obbExtent->z = (maxZ - minZ) * 0.5f;
}
```
6. 计算两个OBB之间的距离
```c++
float computeOBBDistance(Point* obb1Center, Vector* obb1Axis, Vector* obb1Extent, Point* obb2Center, Vector* obb2Axis, Vector* obb2Extent) {
Vector d = { obb2Center->x - obb1Center->x, obb2Center->y - obb1Center->y, obb2Center->z - obb1Center->z };
float distance = fabs(dotProduct(d, *obb1Axis));
distance -= fabs(dotProduct(d, *obb2Axis));
Vector crossProduct = cross(*obb1Axis, *obb2Axis);
distance += fabs(dotProduct(d, crossProduct));
for (int i = 0; i < 3; i++) {
distance -= fabs(dotProduct(crossProduct, Vector{ obb2Extent->x * obb2Axis->x, obb2Extent->y * obb2Axis->y, obb2Extent->z * obb2Axis->z }));
crossProduct = cross(*obb1Axis, Vector{ obb2Axis->x, obb2Axis->y, obb2Axis->z });
distance += fabs(dotProduct(d, crossProduct));
}
return distance;
}
```
以上是使用C++语言编写OBB算法的基本步骤,你可以根据自己的需求进行调整。
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