Three-Dimensional Thermal Mapping from IRT Images for Rapid Architectural Heritage NDT

Abstract

Thermal infrared imaging is fundamental to architectural heritage non-destructive diagnostics. However, thermal sensors’ low spatial resolution allows capturing only very localized phenomena. At the same time, thermal images are commonly collected with independence of geometry, meaning that no measurements can be performed on them. Occasionally, these issues have been solved with various approaches integrating multi-sensor instrumentation, resulting in high costs and computational times. The presented work aims at tackling these problems by proposing a workflow for cost-effective three-dimensional thermographic modeling using a thermal camera and a consumer-grade RGB camera. The discussed approach exploits the RGB spectrum images captured with the optical sensor of the thermal camera and image-based multi-view stereo techniques to reconstruct architectural features’ geometry. The thermal and optical sensors are calibrated employing custom-made low-cost targets. Subsequently, the necessary geometric transformations between undistorted thermal infrared and optical images are calculated to replace them in the photogrammetric scene and map the models with thermal texture. The method’s metric accuracy is evaluated by conducting comparisons with different sensors and the efficiency by assessing how the results can assist the better interpretation of the present thermal phenomena. The conducted application demonstrates the metric and radiometric performance of the proposed approach and the straightforward implementability for thermographic surveys, as well as its usefulness for cost-effective historical building assessments.

A Multi-Analytical Study for the Enhancement and Accessibility of Archaeological Heritage: The Churches of San Nicola and San Basilio in Motta Sant’Agata (RC, Italy)

“…Finally, infrared thermography is a close-range sensing diagnostic technique, whose use is now well-consolidated for the study of buildings, paintings and finds. It is a noninvasive and non-destructive imaging approach that uses a sensor in order to record the emitted infrared radiations from a surface, returning a thermal map (a raster where the single cells contain temperature values) [43]. When the thermal emission of an object is monitored under natural conditions, it is referred to as passive thermography.…”

Combining Multiband Imaging, Photogrammetric Techniques, and FOSS GIS for Affordable Degradation Mapping of Stone Monuments

“…For this case study, photogrammetric approaches were followed using multiband datasets (examples of reflectance images shown in Figure 17), as described in Section 3.2, to generate the necessary base maps for the mapping process. The thermal orthoimage mosaic was produced following a hybrid approach exploiting both the visible and thermal images captured by the FLIR One Pro camera [58] (Figure 18). The false-color multiband image mosaic composed of three single-band mosaics (RGB, NIR, and TIR) was classified to create the thematic map (true-color image shown in Figure 19 and final degradation pam in Figure 20).…”

3D Thermal Mapping of Architectural Heritage

“…Since the thermographic images were not used for generating the geometric model, a higher number of points was reconstructed, resulting in an accurate higher resolution model. Simultaneously, the spatial resolution of the thermal information was higher due to the large number of used TIR images that were acquired from a close range [30].…”