Lastly, ISO 9869-2:2018, 2018 provides a standardized method that incorporates infrared imaging into the on-site, experimental assessment of U-values on the walls of buildings. This method is limited to walls with a low thermal mass, and measurement campaigns span several days, during which only night-time measurements are used for calculation. However, some authors state that a reliable value of the U-value can be extracted in short measurement times [28]. Our experiments were conducted on the first floor of the Business Incubator Centre Building at the University of Castilla La Mancha by following the U-value measurement guidance, which requires a relevant (large and stable) indoor-outdoor temperature gradient (following [20]). Moreover, the measurements were performed without heating and cooling systems. The U-values were calculated for the objects \"window-frames\" and \"wall areas\" of the structural elements #E6 of Zone 1 (East01) and #SE11 of Zone 5 (Weast02). These are two exterior structural elements with different orientations (east and west, respectively). In all cases, we took 5-h average values with indoor-outdoor gradients of around 10 \({}^{\circ}\)C.

The constructive and thermal characteristics that constitute these spaces correspond to the standards for the place and the date of construction of the building. The first and fourth columns of Table 4 present the average nominal transmittances (U\({}_{\text{t}}\)) corresponding to the window-frames and wall areas of this building, which must be taken as approximate values. This information is included merely in order to evaluate the variation with respect to the empirical values computed from Equations (5)-(8). The results obtained when using the original temperatures provided by the thermal camera are shown in the columns denoted as U\({}_{\text{o}}\). In this case, Equations (1)-(4) were omitted, and the variable _T_(object_r)_ was replaced with the original temperature (that provided by the thermal camera) without correcting Equation (7). In addition, for these cases, the standard emissivity of materials similar to existing ones were taken, in our case, aluminium (window-frames) and plaster (wall area). Column U\({}_{\text{c}}\) corresponds to the U-values calculated after making corrections I and II. Finally, relative errors E\({}_{\text{o}}\) and E\({}_{\text{c}}\) with respect to the nominal values are included. These results show a significant variation in the empirical U-values without and with the correction proposed in this paper. It is clear that the relative errors decrease when corrections I and II are carried out. ## 7 Conclusions

The objective of this paper is to show a methodology that corrects the apparent temperature provided by a thermal camera which, together with a 3D scanner, generates the thermal point cloud of an indoor scene. As shown in Section 1, this problem has not yet \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & **T\({}_{\text{o}}\)**(\({}^{\circ}\)C) & **T\({}_{\text{i}}\)**(\({}^{\circ}\)C) & **R** & **U\({}_{\text{t}}\)** & **U\({}_{\text{0}}\)** & **E\({}_{\text{o}}\)**(\%) & **U\({}_{\text{c}}\)** & **E\({}_{\text{c}}\)**(\%)** \\ \hline \#SE6 & & & & & & & & \\ Zone1 & 7.5 & 17.5 & 42 & Window-frame & 2.1 & 0.83 & 60.4 & 1.67 & 20.4 \\  & & & & Wall-area & 1.32 & 0.07 & 94.6 & 0.97 & 26.5 \\ \hline \#SE11 & & & & & & & & \\ Zone5 & 7.4 & 17.6 & 41 & Window-frame & 2.10 & 1.56 & 25.7 & 1.87 & 10.9 \\  & & & & Wall-area & 1.32 & 0.07 & 94.6 & 0.93 & 29.0 \\ \hline \end{tabular}
\end{table} 
Table 4: Comparison of transmittance values (W/m\({}^{2}\)\({}^{\circ}\)K) in #SE6 of Zone 1 and #SE11 of Zone 5. T\({}_{\text{o}}\) = Outside air temperature (\({}^{\circ}\)C), Ti = Inside air temperature (\({}^{\circ}\)C), R = Relative humidity (%), U\({}_{\text{t}}\) = average nominal U-value, U\({}_{\text{o}}\) = calculated U-value without correction and U\({}_{\text{c}}\) = calculated U-value with corrections I and II.