To work with the 3D model of the megalithic tomb and create reconstructions, the stones, which were cut out of the complete 3D model, had to be closed. Two new textures were added to each stone: a basic grey stone texture to the original mesh and a checkerd black/white texture to the added material closing the megaliths, which was done by using the Screened Poisson Surface Reconstruction algorithm in the software CloudCompare.
To close these 3D megaliths without creating an unrepeatable workflow for all megaliths individually, the Screened Poisson Surface Reconstruction algorithm by Kazhdan and Hoppe (2013) was used. This algorithm was used in the computer software CloudCompare and closes the 3D models of the cut-out megaliths based on not only the missing area, but also the existing mesh around the area. The technique does not perfectly recreate the surface, it will close the missing area as best it can from the information of the surrounding area of the absent section. There is still some degree of uncertainty in the reconstruction with the algorithm, but as the area of the cut out is in most cases too large to correctly reconstruct the area, the reconstructed surface was visibly separated with a different texture. Because a defined workflow is used for each stone in combination with the Screened Poisson Surface Reconstruction algorithm in CloudCompare, the filling of these megaliths is replicable.
The Screened Poisson Surface Reconstruction algorithm used in the software CloudCompare (Image: LWL-Altertumskommission für Westfalen/Klinke)
While the original textures were used for the Düwelsteene model from 2017 and they still show the megalithic tomb with the correct appearance and colour, the texture of each individual stone could not be kept for the digital reconstructions of the tomb. After fixing the holes with the Screened Poisson Surface Reconstruction algorithm, that were created by cutting each stone from the entire Düwelsteene 3D model, the texture could not be added back to the megaliths. The reason for using a new texture was that the UV map of the prior 3D model was not mapped efficiently for further tasks. To still display the megaliths of the tomb as rocks and not simply colour them grey, a basic rock texture was added to the models of the megaliths.
To distinguish the scanned 3D meshes of the megaliths from the Düwelsteene and the mesh from the Poisson Surface reconstruction, the added areas were converted in Blender to be visible as a black and white checkered texture.
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