Panoramic Image Generation Using Centerline- Constrained Mesh Parameterization for Arbitrarily Shaped Tunnel Lining

Three-dimensional (3D) triangular meshes has been widely used in tunnel engineering. This paper proposes an algorithm for unwrapping 3D tunnel lining meshes into straight two-dimensional (2D) meshes to generate a 2D seamless panoramic image of the tunnel lining. The proposed algorithm is divided into three steps. In the first step, the centerline is extracted and the L1-median is used to represent the centerline of the tunnel; in the second step, a centerline constraint, which is linear to ensure that the equations to be solved are also linear, is added to least squares conformal mapping (LSCM) to unwrap the tunnel mesh; and in the third step, a panoramic image of the tunnel lining is obtained through texture projection or image correction. Adding a centerline constraint allows the panoramic image to retain mileage information and global shape. The strict geometric relationship between the 3D mesh and panorama guarantees the panorama's accuracy and realizes the two-way mapping of 2D and 3D data analyses. Moreover, a projection strategy is proposed to efficiently process the multiple tiles and non-manifold tunnel meshes which cannot be unwrapped directly using mesh parameterization algorithms. The experimental results show that centerline-constrained LSCM (CLSCM), which is suitable for any arbitrarily shaped tunnel lining, can preserve the global shape and local details better than the conventional method and can be extended to unwrap any strip-shaped structured meshes.