Surveying of buildings with the laser scanner method
It proves to be particularly suitable in the case of buildings with a geometrically complex architecture and in the case where, apart from the geometry, surveying is done in order to obtain the colorimetry, the decay or the frescoes found on the revealed surfaces. The surveying consists of obtaining a high-resolution point cloud.
Depending on the complexity of the object to be revealed we can choose a mesh of points beginning at 2 mm x 2 mm, for example suitable to the surveying of parts as complexly decorated as capitals, cornices, bas-reliefs etc. and then move on to a less dense mesh of a few centimeters, for example for the surveying of flat walls, floors etc. At the same time, while these points are being obtained, photographs are captured using professional high-resolution cameras.
Depending on the distance from the revealed object, we use calibrated 20, 50 or 80 mm lenses.
The overall point cloud is obtained by assembling the individual georeference scans through the acquisition of appropriate tags. The error due to the pairing of the clouds is contained within a few millimeters. The point cloud thus obtained contains all the information of the revealed object.
By subsequent processing we can obtain the colored point clouds, the three-dimensional model with the images developed on the three-dimensional surface from which we can extract sections or diagrams.
From this model, we can obtain the orthogonal orthophotographs on any level
2D and 3D graphic rendering. Whichever surveying method is being used for data acquisition, the graphic rendering remains a fundamental point which attracts a great deal of attention. In the two-dimensional design of diagrams, perspectives and sections of buildings of historical significance, special attention is given to the proportions of the architectural layout and to the geometry of the decorative elements and the sub-elements that make them up as capitals, shafts, moldings etc. When possible, for the purposes of a consistent rendering of the design, we compare the geometries revealed to the conventional geometries found on textbooks or historical works. Special attention is also given to the design of representational elements such as statues, bas-reliefs, festoons etc., or frescoes. The graphic rendering in these cases follows an appropriate stylistic research which is different each time, aiming at interpreting the aesthetic expression of the object to be restored in a consistent way. With the same attention to proportions and geometries, accurate three-dimensional models are rendered, focused on historical research or prototyping and scale reproduction.
[by Alberto Raschieri, GEOMAR.IT s.n.c.]