## 3 Results  
### Stereo Camera Calibration  
The reprojection error, expressed as the mean value on the X- and Y-axis of the fiducial points found in the chosen pair of bands, clearly showed the bias on calibration accuracy (Figure 2). The overall trend of the reprojection error for several bands (G, B, NIR, and RE) showed a uniform behavior for all pairs of bands relative to the distance. Notably, higher errors were observed at extreme distances (500 mm and 1500 mm), while the lowest error values occurred at intermediate distances, particularly between 600 mm and 700 mm, for both the X and Y coordinates. The reprojection error tended \begin{table}
\begin{tabular}{l l l} \hline \hline \multicolumn{1}{c}{**V Vegetation Indices**} & \multicolumn{1}{c}{**Formula**} & \multicolumn{1}{c}{**References**} \\ \hline
**NDVI** (Normalized Difference Vegetation Index) & (NIR \(-\) RED)/(NIR \(+\) RED) & [39] \\
**MCARI** (Modified Chlorophylll Absorption in Reflectance Index) & [(RE \(-\) RED) \(-\) 0.2 \(\times\) (RE\(-\)G)] \(\times\) (RED/RE) & [39] \\
**SR** (Spectral Ratio) & RED/NIR & [40] \\
**CLr** (Chlorophyll Red Index) & (RED/NIR) \(-\) 1 & [41] \\
**NARI** (Normalized Antocyanine Reflectance Index) & (1/C \(+\) 1/RED)/(1/G \(-\) 1/RED) & [42] \\
**ARI** (Anthocyanin Reflectance Index) & (1/G \(-\) 1/RED) & [19] \\
**mARI** (Modified Anthocyanin Reflectance Index) & (1/G \(-\) 1/RE) \(\times\) NIR & [19] \\
**GNDVI** (Green Normalized Difference Vegetation Index) & (NIR \(+\) G)/(NIR \(-\) G) & [43] \\
**SIPI** (Structural Independent Pigment Index) & (NIR \(+\) RED)/(NIR \(-\) B) & [44] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Multispectral band ratios for the calculation of vegetation indices used in this study. to increase with increasing distance, as shown in previous studies [45], while the error at lower distances could be due to the high resolution of the camera, which reduced the detected fiducial point size at these distances during the calibration process. However, the bands showed differing behavior for errors along the axes. While the B and RE bands exhibited lower accuracy along the X axis, the error along the Y axis was generally more significant for the G band. The NR band, conversely, showed a homogeneous trend across both axes, with no notable impact from a single axis. Despite these variations, the average values of the reprojection error, calculated for both the x- and y-axis, at the analyzed distances indicated a well-calibrated model. Figure 3 shows that the overall reprojection error of calibration patterns was much less than 1 pixel. This result demonstrated that despite the observed variability, the system maintained good accuracy for practical applications within the calibration range. Table 2 summarizes the performance of the depth estimation (Z) in mm at several distances for the spectral band combinations (G vs. R, B vs. R, NR vs. R, and RE vs. R). Overall, it was observed that the percentage error (Err%) associated with each stereo system increased proportionally to the distance. As expected, this behavior reflected the performance limitations previously identified in the calibration dataset. The best results were observed at the shortest distance (800 mm), with percentage errors of 18.36%, 8.85%, 6.20%, and 4.72% for the G, NR, B, and RE bands, respectively. The worst results were estimated at 1000 mm, with percentage errors of 23.22%, 14.31%, 11.60%, and 10.41% for the G, NR, B, and RE bands, respectively. Figure 2: Averages of the x-axis and y-axis reprojection errors (pixels) for the stereo setups of the G, B, NR, and RE bands to the R band as a function of distance. The B and RE spectral bands were found to be more accurate than the G and NR combinations, with lower percentage errors. Among the proposed stereo systems, the G band showed the worst performance, suggesting that the reprojection error observed on the Y-axis may have significantly impacted the accuracy of this stereo configuration.