【ChatGPT】Python 实现计算两线段的变换矩阵

使用 chatgpt 问的问题：

作为一个数学专家，请给出下面的这个问题的数学解法；
要求如下：
1. 给出数学推理公式
2. 给出 python 的实现方式

已知条件：
1. 三维空间中，线段L1，L1 由点 A1 (ax1, ay1, az1) 与 B1 (bx1, by1, bz1) 组成； 
2. 三维空间中，空间线段L2， L2 由 点 A2 (ax2, ay2, az2) 与 B2 (bx2, by2, bz2) 组成； 
3. 线段 L2 是由线段 L1  通过 4 * 4 的 变化矩阵 M 得到

求解变换矩阵 M，并将 M 分解为平移矩阵与旋转矩阵；

回答如下：

To solve the problem of finding the transformation matrix that maps line segment to line segment in 3D space, we will utilize concepts from linear algebra. The transformation can be described as a combination of rotation and translation.

1. Mathematical Formulation

Representation of Points: Let:

Points of line segment be and .
Points of line segment be and .
Parameters of Lines: The direction vectors of the line segments are:

Translation : The translation component can be computed as:

Rotation Matrix : To find the rotation matrix that aligns with , we can use the following approach:

Normalize the direction vectors:
Compute the rotation axis using the cross product:
Calculate the angle between the two direction vectors using the dot product:
Use Rodrigues’ rotation formula to construct the rotation matrix .

2. Python Implementation

python 实现如下：

import numpy as np

def compute_transformation(A1, B1, A2, B2):
    # Convert points to numpy arrays
    A1 = np.array(A1)
    B1 = np.array(B1)
    A2 = np.array(A2)
    B2 = np.array(B2)

    # Compute direction vectors
    d1 = B1 - A1
    d2 = B2 - A2

    # Compute translation component
    T = A2 - A1

    # Normalize direction vectors
    norm_d1 = np.linalg.norm(d1)
    norm_d2 = np.linalg.norm(d2)
    if norm_d1 == 0 or norm_d2 == 0:
        raise ValueError("Direction vectors must be non-zero")
    
    u = d1 / norm_d1
    v = d2 / norm_d2

    # Compute rotation axis and angle
    rotation_axis = np.cross(u, v)
    angle = np.arccos(np.clip(np.dot(u, v), -1.0, 1.0))

    # If the rotation axis is a zero vector, u and v are parallel
    if np.linalg.norm(rotation_axis) == 0:
        R = np.eye(3)  # No rotation needed
    else:
        rotation_axis = rotation_axis / np.linalg.norm(rotation_axis)
        K = np.array([[0, -rotation_axis[2], rotation_axis[1]],
                      [rotation_axis[2], 0, -rotation_axis[0]],
                      [-rotation_axis[1], rotation_axis[0], 0]])
        R = (np.eye(3) + 
             np.sin(angle) * K + 
             (1 - np.cos(angle)) * np.dot(K, K))

    return R, T

A1 = (1, 2, 3)
B1 = (4, 5, 6)
A2 = (7, 8, 9)
B2 = (10, 11, 12)

R, T = compute_transformation(A1, B1, A2, B2)

print("Rotation Matrix R:")
print(R)
print("\nTranslation Vector T:")
print(T)

3. 对代码的解释：

The function compute_transformation takes the endpoints of two line segments as inputs.
It calculates the direction vectors, translation vector, and rotation matrix.
The rotation matrix is calculated using the Rodrigues’ rotation formula approach.
The function returns the rotation matrix and translation vector .
This code should give you a good foundation to find the transformation matrix that maps segment to . Adjust the input values of and to test different segments.