## 3 Results
### Data Preparation
#### 3.2.1 Preparation of 3D Data  
As mentioned, for online use, 3D digitized data must be optimized. The methodology employed for this project is structured in several steps. The first step was already described, where the generated raw 3D model is simplified in two versions: one with 10 million polygons, retaining all of the detailed geometry, and one with 500,000 polygons that loosely retains the geometrical features. The second step is to split the low-poly mesh into the parts (or sections) of interest. These parts of the general model are selected to highlight certain building elements or to correspond to the investigated multimodal imaging areas. Blender 3.6.5 LTS was used for this stage. Photogrammetric processing for the 3D surface of the church resulted in two 3D mesh models (one for aerial photogrammetry and the other one for terrestrial photogrammetry), with each mesh model being exported in two versions: high and low poly. In Blender, these meshes had to be re-oriented (repositioned and rotated) so that the final exported scene for online use would be correctly displayed. The colour texture and normal map baking processes require the source mesh (high poly) and the optimized mesh (low poly) to have the exact same position for a correct bake. For this reason, the low- and high-poly meshes had to be aligned at the same time. This process is performed manually. After this alignment, the low-poly meshes were duplicated. The default colour textures of the duplicates were deleted, as they are going to be baked based on new UV (not to be confused with the acronym for ultraviolet) coordinate maps generated further in the process. Figure 7: UV fluorescence image of the portal on the west side, with details on the difference between the original and the AI-denoised images. Then, the low-poly models were cleaned and cut to resemble the complete shape of the church 3D model. Now, these unified models can be split into the sections of interest (see Figure 8). For each church section, the UV coordinate map was regenerated (a process known as topology) for easier referencing of other imaging data, and a new texture was created. In this case, where all the parts are planar, the easiest method to generate a UV coordinate map that best resembles the topology of the walls was the Project from View unwrapping method, provided that the view was adjusted to be perpendicular to the wall part, and the viewport camera was set to orthographic. With the new UV coordinate maps, the colour information is baked from the original low-poly mesh into the new textures of the duplicates and saved as separate image files. The baking method used was Blender Cycles' rendering engine's own baking feature with the Selected to Active feature turned on (meaning the colour from the selected mesh was baked into the active one--the duplicate). Figure 9 shows the distribution of the polygons representing the south have wall selection (shown in orange) in the original UV coordinate map as it was generated by Metashape, as well as the original texture for the whole church. In the same figure, the new regenerated UV coordinate map of the south have wall is shown after it was separated from the main mesh. The baked colour texture with the new UV coordinates is now helpful in referencing other imaging data. The third step is to recover all of the geometrical details for the low-poly mesh from the high-poly one. This can be carried out using many methods. The most efficient method from our point of view is the use of Adobe Substance 3D Painter 2022 v 8.3.1 (Steam Edition) by baking the normal maps from the high-poly mesh and exporting them as textures. First, the 3D models with the new UV coordinate maps and orientation (due to the alignment) are exported together with their high-poly pairs. In Substance 3D Painter, the low-poly model is imported, and, on the baking screen, normal maps are generated based on the corresponding high-poly model. The mesh maps generated are exported as image files (in this case, PNG file format) for each 3D model section.