High resolution 3-D modelling of cylinder shape bodies applied to ancient columns of a church

Abstract

Abstract. The use of Non-Destructive Testing (NDT) applied to construction materials allows to highlight and characterize their features, especially in the case of old buildings. The multi-technique high resolution 3D modelling described here is aimed to investigate the conservation state of the central column of a colonnade in the ancient church of Saints Lorenzo and Pancratio, dating to about the second half of the thirteenth century and located in the old town of Cagliari (Italy). This column was considered of interest because its longitudinal axis deviates from its ideal position and it appears the most deteriorated. In this work we describe the integrated application of 3D diagnostic methods, i.e. Terrestrial Laser Scanner (TLS), close range photogrammetry (CRP) and ultrasonic tomography supported by petrographic investigations. They were used to improve the diagnostic process of the conservation state of the investigated column. The TLS technique was supported by CRP to obtain a natural colour texturized 3D model of the column. The geometrical anomaly maps derived from the data of the TLS-CRP survey show the presence of some anomalies worthy of attention. Starting from the 3D reconstruction with previous techniques we planned and implemented a 3D ultrasonic tomography. Ultrasonic tomography proved to be a successful tool in identifying internal defects, as well as the presence of voids and flaws within the materials through the analysis of the propagation of ultrasonic waves. The integration of the three non-invasive techniques supported by petrographical analyses demonstrates its potential in reducing ambiguities since each technique brings its clue to the overall diagnostic process.

3D Imaging of CRP and Ultrasonic Tomography to Detect Decay in a Living Adult Holm Oak (Quercus ilex L.) in Sardinia (Italy)

“…The 2D images were carefully selected and preprocessed with release 1.6 of Agisoft Metashape ® software (Agisoft LLC, St. Petersburg, Russia) based on Structure from Motion (SfM) methodology to avoid the use of noising data to finely align poses and generate a high dense points cloud textured with natural colors [6,22]. Three high density (each of about 10 million points) unstructured, unified, registered point clouds were restituted after image processing.…”

“…To improve the signal/noise ratio and thus data quality, a stack of six waveforms was carried out for each measurement, both in laboratory and in the field. The transit times were measured by locating the first break of the received longitudinal stacked signals as a result of the analysis of the waveforms recorded and displayed by the portable oscilloscope Fluke 96b [20,22,25]. The longitudinal velocity (Vp) was computed, considering the ratio between the path length (L) and the transit time of the longitudinal ultrasonic signal (T).…”

“…For instance, CRP can provide 3D high resolution measurable models useful in the application of 3D ultrasonic tomography. The integration of geomatic and acoustic techniques is adopted in many fields of the applied sciences [6,[18][19][20][21][22].…”

Close-Range Sensing and Data Fusion for Built Heritage Inspection and Monitoring—A Review

“…Ultrasonic and sonic sensing, likewise, have lower spatial resolution than TLS and close-range photogrammetry. However, the registration of ultrasonic/sonic measurements with color-textured 3D models and backscattered laser intensity-textured 3D models, from photogrammetry and TLS, respectively, can benefit the interpretation of shallow and inner anomalies of columns and pillars [313,314]. At the same time, referencing of longitudinal wave velocity maps or tomographic slices helps the better understanding of a historical asset's structural condition in three dimensions, especially when integrated with deformation maps [236,237].…”

Decay Detection in an Ancient Column with Combined Close-Range Photogrammetry (CRP) and Ultrasonic Tomography

“…Non-destructive techniques are constantly being improved in many fields of the applied sciences, as described by numerous authors [3][4][5][6][7][8][9][10][11][12][13]. For instance, contactless remote and proximal sensing methods can represent an optimal solution for the 3D accurate modelling of architectural elements.…”