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.

No abstract

This paper presents the results of a project in which a correlation was made between the results of qualitative and quantitative analyses of the state of plaster on the facade of Valentino Castle in Turin, Italy. The aim of the project was to assess its condition in order to plan restoration work.Surveys (including JR thermographic scanning, knocking tests and surface color inspection) were undertaken over a three years period in different seasons and conditions (shade, direct sunlight, etc.), so that the effects of outside temperature, internal heating and solar radiation could be taken into account. The results were then superimposed so that real defects could be distinguished from apparent ones. An attempt was made to identify a typical thermal trend for each kind of defect.Good correspondence was generally obtained between thermal anomalies revealed by JR surveys and data from the knocking test. However, qualitative analysis was not always adequate to identify the type of damage. More detailed information was obtained from quantitative methods, but the time-consuming analysis involved made it necessary to integrate the two approaches: qualitative methods being used to identify problem areas, then detailed analysis being undertaken with quantitative methods.

The combination of thermographic and geometric recording has always been an issue for architectural heritage diagnostic investigations. Multidisciplinary projects often require integrating multi-sensor informationincluding metric and temperature data-to extract valid conclusions regarding the state-of-preservation of historical buildings. Towards this direction, recent technological advancements in thermographic cameras and three-dimensional (3D) documentation instrumentation and software have contributed significantly, assisting the rapid creation of detailed 3D thermal-textured results, which can be exploited for non-destructive diagnostical surveys. This paper aims to briefly review and evaluate the current workflows for thermographic architectural 3D modeling, which implement state-of-the-art sensing procedures and processing techniques, while also presenting some applications on case studies of significant heritage value to help discuss current problems and identify topics for relevant future research.