Documentation methodology with Rhinoceros 3D

Documentation methodology with Rhinoceros on the 3D model of wood sculpture

To conduct the work of 3D documentation of the restoration works, after numerous experiments of 3D modeling software, Rhinoceros has been used in the Surveying and Documentation Office of the ISCR[1] thanks to its versatility. The methodology found for the documentation is somewhat complex to use for a restorer for the slowness of certain operations, such as the coloring of a closed area.

In this short text we show part of the documentation work performed by one of our students on the occasion of her graduation thesis (polychrome wooden sculpture representing St. John the Baptist, from the church of San Marco di Norcia (PG) by an unknown Umbrian artist, ascribable to the late sixteenth or early seventeenth century).

We use the 'polylineonmesh' command to create closed lines and opened lines (Fig.1).

Figure 1

The green lines are simply polylines on meshes with a higher thickness for printing purposes; the magenta lines follow the outline of areas to be built.

The closed lines are used only as a guide to then make a colored pattern that highlights the areas (Fig. 2). Unfortunately, there is no command that can accurately fill out the closed polylines located on the complex meshes with patterns, so you have to apply the several commands depending on the specific case.

To idetntify the larger parts of the work we usually divide the mesh and we assigne to each element a material with a more or less transparent color, so that not completely cover the texture working on a different file.

The methodology adapted for the execution of the smaller fields consists in creating a surface starting from the precisely mapped area (using one of these commands: 'patch', 'loft', or 'drape' depending on your needs).To resolve the inconvenience of the imperfect visualization of the surface on the mesh we make thin polysurfaces using the command 'offsetsrf' that all the points on the surface overlap the part of the mesh that you want to highlight in color.

To solve the stained effect due to the surface of the offset in contact with the mesh following the contribution of color transparency, we separate the polysurface with the 'explode' command and delete the surface at the base (Fig. 3).

Figure 2

Blue fields related to magenta polylines in Figure 1.

Only for the areas with the most complicated morphology we use the 'estractmeshfaces' command, like the area with exposed woodworm galleries located on the left arm of the sculpture in the figure.This command is more precise but produces a copy of the area behind it and in a job where it is necessary to produce a large amount of data, it is not very practical. In this specific case, were found also display problems, so in some cases it was necessary to use the offset area of the copied mesh also in this case (Fig. 4).

In the specific case of the mapping of the woodworm holes, to compensate for the lack of a command that allows to make circular mappings on mesh, we used the expedient to make many small polylines on mesh, enlarging the thickness of the line for visual printing purposes (Fig. 5).

To make the documentation work in a faster and more uniform way, it would be useful to have a single command capable of filling the mesh perfectly, without using too many devices depending on the case.