Direct Linear Transform (DLT) is fundamentally connected to triangulation through its ability to solve the intersection of projection rays. Here's how they relate: **Mathematical Foundation:** 1. **Projection Model** - A 3D point $X = [X,Y,Z,1]^T$ projects to 2D point $x = [u,v,1]^T$ through: $\lambda x = PX$ where $P$ is the 3×4 projection matrix $\lambda$ is the projective depth 2. **DLT Formulation** - For each image point, we can write: $\lambda u = \frac{P_{1}^TX}{P_{3}^TX}$ $\lambda v = \frac{P_{2}^TX}{P_{3}^TX}$ - This leads to linear equations: $uP_{3}^TX - P_{1}^TX = 0$ $vP_{3}^TX - P_{2}^TX = 0$ 3. **Triangulation System** - For two views with points $x_1=(u_1,v_1)$ and $x_2=(u_2,v_2)$: $$\begin{bmatrix} u_1P_{3,1}^T - P_{1,1}^T \\ v_1P_{3,1}^T - P_{2,1}^T \\ u_2P_{3,2}^T - P_{1,2}^T \\ v_2P_{3,2}^T - P_{2,2}^T \end{bmatrix} X = 0$$ **Why DLT Works for Triangulation:** 1. **Geometric Interpretation** - DLT finds the 3D point that minimizes algebraic error - Each row in the equation system represents a constraint from one coordinate - The solution is the intersection of projection rays in 3D space 2. **Solution Method** - The system $AX = 0$ is solved using SVD - The solution is the eigenvector corresponding to smallest singular value - This provides the optimal 3D point in a least-squares sense 3. **Implementation Connection** In your code: ```python A = [ point1[1]*P1[2,:] - P1[1,:], P1[0,:] - point1[0]*P1[2,:], point2[1]*P2[2,:] - P2[1,:], P2[0,:] - point2[0]*P2[2,:], ] ``` This directly implements the linear system described above. **Advantages:** - Linear solution - Simple to implement - Works with multiple views - Computationally efficient **Limitations:** - Sensitive to noise - Assumes perfect point correspondences - Minimizes algebraic (not geometric) error