问题:如何将一个3X1的VectorA转换为一个3X3的MatrixA?
解:从3D角度来看,一个3X3的矩阵可以被看作是由3个正交的向量组成的坐标系,因此相较于向量,矩阵包含更为丰富的信息量。因此,对于特定的向量A,可以有无数个对应的矩阵,只需要其中一个矩阵的3个向量中的一个与向量A一致即可。可以假设向量A作为矩阵的Z轴(其他轴同样适用),通过叉乘得到Z轴和绝对Y轴的方向,进而得到矩阵的X轴,再通过矩阵的X轴和向量A的叉乘得到矩阵的Y轴,从而得到MatrixA。
以下是代码:
```C++
struct Mat3x3 {
Vec3 column1;
Vec3 column2;
Vec3 column3;
void makeRotationDir(const Vec3& direction, const Vec3& up = Vec3(0,1,0)) {
Vec3 xaxis = Vec3::Cross(up, direction);
xaxis.normalizeFast();
Vec3 yaxis = Vec3::Cross(direction, xaxis);
yaxis.normalizeFast();
column1.x = xaxis.x;
column1.y = yaxis.x;
column1.z = direction.x;
column2.x = xaxis.y;
column2.y = yaxis.y;
column2.z = direction.y;
column3.x = xaxis.z;
column3.y = yaxis.z;
column3.z = direction.z;
}
}
VBA
Sub DirToRotationMatrix(vectorZ(), RotationMatrix())
Dim vectorTemp(2) 'As Double
vectorTemp(0) = 0 : vectorTemp(1) = 0 : vectorTemp(2) = 1
If vectorZ(0) = 0 And vectorZ(1) = 0 Then
vectorTemp(0) = 0 : vectorTemp(1) = 1 : vectorTemp(2) = 0
End If
Dim vectorX(2) 'As Double Common.Matrix.crossProduct(vectorTemp, vectorZ, vectorX)
NormalizeVector(vectorX, vectorX)
Dim vectorY(2) 'As Double
Common.Matrix.crossProduct(vectorZ, vectorX, vectorY)
NormalizeVector(vectorY, vectorY)
RotationMatrix(0) = vectorX(0) : RotationMatrix(3) = vectorY(0) : RotationMatrix(6) = vectorZ(0)
RotationMatrix(1) = vectorX(1) : RotationMatrix(4) = vectorY(1) : RotationMatrix(7) = vectorZ(1)
RotationMatrix(2) = vectorX(2) : RotationMatrix(5) = vector(2) : RotationMatrix(8) = vectorZ(2)
End Sub
```