A methodology for updating 3D solid models of complex monumental structures based on local point-based meshes

Structural changes introduced during the life of monuments contribute to produce complex geometrical configurations that cannot be properly represented in standard solid modeling systems designed for current engineering applications such as finite element analysis (FEA). Likewise, point-based 3D meshes - laser-scanner or photogrammetric -, although capable of constructing detailed representation of surfaces, cannot be used for direct application in structural analysis because they do not produce complete and unambiguous solid models. To tackle this issue, we merged these two approaches into a unified methodology capable of updating a 3D solid model, representing the entire monument as reconstructed in its presumed original configuration, with information from a 3D mesh model containing a detailed geometrical description of the recent structural state of a specific sector of the same monument. The methodology is based on a series of functions that operate in the Mesh and Solid Modeling Space. The mesh model is aligned via 3D registration and, subsequently, segmented for its conversion to a solid model. Finally, this solid updates the solid representation of the entire monument via Boolean operations. We test the procedure on the Main Platform of the Huaca de la Luna, Trujillo, Peru, one of the most important massive earthen structures of the Moche civilization. Solid models are defined in AutoCAD while 3D meshes are constructed via the photogrammetric program Agisoft PhotoScan. The results indicate that the proposed methodology is effective at transferring complex geometrical and topological features from the mesh to the solid modeling space. The updated solid model can be represented and visualized in any standard CAD software, and utilized for FEA and augmented reality applications.