# A Simple Method to Estimate Weed Control Threshold by Using RGB Images from Drones
## 3 Results
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Flight Height** & **Ca-TGC\({}_{\rm{WP+CP}}\)** & **Er-TGC\({}_{\rm{WP+CP}}\)** & **Stat t** & \(p\) & \(r\) \\
**(m)** & **(m2)** & **(m2)** & **(m2)** & **(m2)** & **(m2)** \\ \hline
10 & 0.95 & 0.92 & 0.520 & 0.619 & 0.87 ** \\ \hline
20 & 1.05 & 1.19 & \(-\)1.844 & 0.108 & 0.90 ** \\ \hline \((*=p<0.01)\). & & & & & \\ \end{tabular}
\end{table} 
Table 2: Total green cover in weeded and control plots (WP and CP) was obtained using Canopeo (Ca-TGC\({}_{\rm{WP+CP}}\)) and Erdas (Er-TGC\({}_{\rm{WP+CP}}\)). Student \(t\)-test, \(p\)-value and Pearson correlation coefficient (\(r\)). \begin{table}
\begin{tabular}{c c c c c c} \hline
**Flight Height (m)** & **M1-MGC\({}_{\rm{WP+CP}}\)** & **Er-MGC\({}_{\rm{WP+CP}}\)** & **Stat t** & \(p\) & \(r\) \\
**(m2)** & **(m2)** & **(m2)** & **(m2)** & **(m2)** & **(m2)** \\ \hline
10 & 0.60 & 0.75 & \(-\)5.660 & 0.001 & 0.36 ns \\ \hline
20 & 0.73 & 1.05 & \(-The indices used to evaluate the goodness of fit confirmed the previous results. The values of M1 (Table 5) calculated at 10 m were disappointing both for the MGC (MAE = 1.22 m\({}^{2}\), EF = \(-\)3.85) and for the WCG (RMSE/ \(\hat{\text{O}}\) = 119%, MAE = 1.43 m\({}^{2}\), CRM = \(-\)1.04, EF = \(-\)1.07). At 20 m, almost all indices of M1 worsened, especially those related to the WCG (RMSE/ \(\hat{\text{O}}\) = 158%, MAE = 1.53 m\({}^{2}\), CRM = \(-\)1.41, EF = \(-\)1.28). The indices calculated for RYL at 10 m were not much better (RMSE/\(\hat{\text{O}}\) = 40%, EF = \(-\)0.40, CRM = \(-\)0.27) but, in this case, the fitting improved when passing at 20 m (RMSE/\(\hat{\text{O}}\) = 35%, EF = \(-\)0.05, CRM = \(-\)0.20). Good values of indices were reached only by using M2 (Table 6), especially for the WCG. At 10 m, the results obtained were already acceptable (RMSE = 0.08, MAE = 0.61 m\({}^{2}\), EF = 0.66) and they became even better at 20 m (RMSE = 0.07, MAE = 0.53 m\({}^{2}\), EF = 0.73). Conversely, the trend drawn by RYL was the opposite as, at 10 m, the values of the indices were better than at 20 m (RMSE/\(\hat{\text{O}}\) = 25 and 40%, EF = 0.48 and 0.16, CRM = 0.07 and 0.31 for 10 and 20 m, respectively). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Quality**} & \multicolumn{3}{c}{**M2 at 10 m of Flight Height**} & \multicolumn{3}{c}{**M2 at 20 m of Flight Height**} \\ \cline{2-7}  & **MGC** & **WGC** & **RYL** & **MGC** & **WGC** & **RYL** \\ \hline RMSE & 0.08 & 0.07 & 0.04 & 0.07 & 0.27 & 0.05 \\ RMSE/O & 48 & 10 & 25 & 55 & 26 & 40 \\ MAE & 0.61 & 0.42 & 0.15 & 0.53 & 1.76 & 0.15 \\ EF & 0.66 & 0.10 & 0.48 & 0.73 & \(-\)0.21 & 0.16 \\ CRM & \(-\)0.38 & \(-\)0.01 & 0.07 & \(-\)0.29 & 0.10 & 0.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Modelling quality indices (RMSE, RMSE/\(\hat{\text{O}}\), MAE, EF and CRM for more details see Table 1) used to evaluate the goodness of fit for method 2 (M2) at 10 and 20 m of flight height in estimating the maize green cover (MGC), the weed green cover (WGC) and relative yield loss (RYL). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Flight Height** **(**m)**} & \multirow{2}{*}{**M2-MGCWP+CP** **(**m\({}^{2}\)**)**} & \multirow{2}{*}{**Er-MGCWP+CP** **(**m\({}^{2}\)**)**} & \multirow{2}{*}{**Stat t**} & \multirow{2}{*}{\(p\)**} & \multirow{2}{*}{\(r\)**} \\ \cline{1-1}
10 & 0.76 & 0.75 & 0.386 & 0.711 & 0.36 ns \\ \hline
20 & 0.94 & 1.05 & \(-\)1.172 & 0.280 & 0.06 ns \\ \hline
**Flight Height** **(**m)** & **M2-WGCWP+CP** **(**m\({}^{2}\)**)** & **Er-WGCWP+CP** **(**m\({}^{2}\)**)** & **Stat t** & \(p\)**} & \multirow{2}{*}{\(r\)**} \\ \hline
10 & 0.24 & 0.17 & 3.311 & 0.013 & 0.94 **\({}^{**}\)** \\ \hline
20 & 0.17 & 0.14 & 1.689 & 0.135 & 0.91 **\({}^{**}\)** \\ \hline \hline \end{tabular} (ns = not significant, \({}^{**}=p<0.01\)).  
\end{table} 
Table 4: Maize green cover and weed green cover in weeded and control plots (WP and CP) obtained using method 1 (M2-MGCWP+CP and M2-WGCWP+CP) and Erdas (Er-MGCWP+CP and Er-WGCWP+CP) (Student \(t\)-test).