When faced with the particular conditions posed by the "M" Sepulcher it was decided that a more unconventional approach might not only simplify the task but also provide the capability of representing the object of our study in a radically new way: by virtually recreating the actual surfaces of the walls and vault, in full detail, with the obvious superimposition of the decorations (mosaic or painting) they were adorned with. Although the concept of a computer generated 3D model was not new, it had always been applied to generate, at the most, schematic exemplifications of structures on which to project the images of any surface texture, obtaining a great general effect, but still hardly useful for the purpose of study. We were encouraged in this by the availability of two new instruments: a total station (Leica TCR1103) equipped with a coaxially (along the line of sight) mounted reflectorless EDM laser (not needing reflecting prisms to measure distance) and a 3D digitizer arm, that is a sort of a 3D pantograph (Microscribe 3DLX).
Positioning of total station inside the "M" Sepulcher
The first step was to place the laser EDM total station inside the sepulcher onto a predetermined station tied to the main traverse used in the survey of the Necropolis plan. Through the use of this instrument we were able to scan the different wall and ceiling surfaces, carefully distinguishing the brick and plastered surfaces of the left wall, the mosaic sinopite, the corbel and the frescoed lower portion of the front wall, the sinopite and fresco of the right wall. Furthermore the total station was used to record points for the spatial referencing and geometric rectification of the photographs of the various surfaces. Finally, we recorded the points to be used later to reference 3D digitizer survey sessions (3 points for every session).
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Use of the laser EDM total station to record an array of points representing
each surface
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The above method implies a more discreet number of surveyed points as opposed
to full laser scanning methods; hence the need of an interpolation procedure
to reproduce the surfaces
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Choice of a NURBS (Non Uniform Rational B-Splines) surface generating software
such as Rhinoceros in order to have better control in the creation and
delimitation of surfaces as opposed to direct point to TIN (Triangulated
Irregular Network) procedures
- Union of appropriately positioned points into a series of quasi-parallel crisscrossing curves to act as a "network" for each surface to be generated
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Survey of all points necessary to be used as 3D
Digitizer reference points
- Survey of points to be used as reference for the ortho-rectification of the various surfaces' photographs
