## 4 Experimentation on the Case Study
### Photogrammetric and Scanning 3D Reconstruction  
Preparing for a detailed building assessment involves setting up various technologies employed for the task (i.e., UAS, survey equipment (total station, GNSS receiver) and laser scanner). Each piece of equipment plays a paramount role in ensuring the accuracy and comprehensiveness of the data collected and, finally, project success. A standardised thermographic data acquisition methodology was employed to minimise solar-induced thermal anomalies, limiting data collection to periods outside direct solar irradiance (pre-sunrise and post-sunset). The infrared camera, calibrated to a predetermined focal length, was positioned orthogonally to the facade at a distance of 15-20 m, commensurate with the desired spatial resolution. A minimum of 70% thermogram overlap was ensured to enable subsequent image processing and 3D reconstruction [27]. However, for the photogrammetric flight, a flight altitude of 100 m has been considered to be a balanced approach that enhances coverage and data acquisition efficiency, maintains a high level of detail, ensures safety and compliance, and accounts for environmental factors, making it an optimal choice for conducting comprehensive and effective assessments. At this altitude, the UAS can capture a wide area in a single frame, allowing for efficient data collection, enabling the assessment of large areas in a relatively short time. While higher altitudes provide broader coverage, 100 m represents a practical height that still ensures a good level of detail in the imagery, allowing for sufficient resolution to identify and assess building features. At the same time, flying at this altitude was considered to minimise risks associated with lower-altitude flights, such as potential collisions with buildings, trees, or other obstacles, thus reducing the likelihood of disturbing occupants or passers-by within the area. Flying at 100 m is also aligned with regulatory limits (falling below the 120 m limit) and ensures that the survey adheres to legal requirements while still achieving its objectives. In addition, at moderate altitudes like 100 m, UAS are more stable and less affected by wind gusts compared to flying at higher altitudes, which results in more consistent and reliable data collection. When evaluating the model's accuracy, the height of the objects and the shutter area were taken into account. The experimental design employs simplified, idealised shading scenarios to elucidate the practitioner's methodology for quantifying the influence of obstruction amplitude on calculations pertaining to standardised building height assessments [28]. To enhance the precision, reliability, and utility of UAS mapping, it is essential to integrate georeferenced targets at the ground level, as they ensure that the captured data are not only visually representative but also spatially accurate and aligned with real-world coordinates. These targets, also known as Ground Control Points (GCPs) (Figure 8a) are specific, marked locations on the ground. Their coordinates were determined using high-accuracy GNSS equipment (Figure 8b). When UAS captures images from the air, georeferenced targets help to accurately align aerial data with real-world coordinates, improving the spatial accuracy of resulting maps or 3D models. The GCPs provide additional reference points that can be used to correct systematic errors in the UAS's positioning data (e.g., GPS inaccuracies, camera lens distortion, or UAV's flight instability). They are also useful for  
Figure 7: UAV flight areas in Romania (detail for Timisoara). defining the aerial image scale, ensuring that measurements are precise and reliable. The inclusion of GCPs allows for a robust quality control process, where the accuracy of the UAS mapping can be validated by comparing the locations of the GCPs as they appear in the aerial data against their known coordinates.