# A Quantitative Evaluation of UAV Flight Parameters for SfM-Based 3D Reconstruction of Buildings
## 4 Validation
### Analysis of Multiple Shooting Patterns
#### 4.2.1 Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS)  
Composite shooting pattern strategies offer the potential to leverage the advantages of various individual patterns, but at the same time, the performance criteria that need to be evaluated become more complex. In this study, we applied the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), one of the multi-criteria decision-making (MCDM) techniques, to comprehensively consider multiple performance criteria and evaluate the overall effectiveness or preference of various composite shooting pattern combinations, thereby determining their relative rankings. The analysis considered a total of seven performance criteria, including input-related indicators such as computation time, number of images used, and reprojection error, as well as output-related indicators such as final point count, reconstruction completeness, point density, and average track length.  
In this analysis, equal weights were assigned to all performance criteria to calculate the comprehensive performance score for each composite shooting pattern combination (Table 10). The naming convention for each analysis is \"[Shooting Type]_O[Distance Value (m)]\" (e.g., C_O20: Circular pattern offset distance 20 m). According to the TOPSIS analysis results, the composite shooting pattern named C_O40_S_O30 (Circular pattern offset distance 40 m and Surface pattern offset distance 30 m) achieved the highest overall efficiency score (TOPSIS Score: 0.691) and was selected as the top-ranked combination with the best performance under the evaluated criteria.  
Following closely behind were C_O20_S_O30 (Score: 0.687), S_O30_A_O40 (Score: 0.686), and C_O40_A_O20 (Score: 0.683), which formed the top ranks with minimal score differences, demonstrating high overall performance. On the other hand, the S_O10_S_O20 combination recorded the lowest score (Score: 0.330) and was evaluated  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Topsis Rank** & **Pattern1** & **Pattern2** & **Topsis DistIdeal** & **Topsis DistNegIdeal** & **Topsis Score** \\ \hline
1 & C\_O40 & L\_O30 & 0.039644 & 0.088516 & 0.69067 \\
2 & C\_O20 & L\_O30 & 0.041811 & 0.091929 & 0.687373 \\
3 & L\_O30 & P\_O40 & 0.041934 &  
as the least efficient composite shooting pattern under the same weighting conditions as the criteria considered in this analysis. In summary, this result indicates that a complex shooting path plan that maximizes the estimation of architectural features is more beneficial for 3D reconstruction than a method that collects as many detailed images as possible from nearby shooting points.  
In conclusion, by applying the TOPSIS method, we were able to integrate multiple conflicting performance criteria into a single quantitative score, enabling an objective comparison of the 'overall performance' of various composite shooting patterns and assigning relative priorities. The composite shooting pattern combinations ranked at the top in this analysis (C_O40_S_O30, C_O20_S_O30, etc.) can be considered as promising candidate strategies for achieving overall effective 3D modeling results under resource-constrained environments (e.g., time, cost).