# The Influence of the Quality of Digital Elevation Data on the Modelling of Terrain Vehicle Movement
## 3 Results
### Efficiency Improvements of the Elevation Models  
Before any wider global data improvements were introduced, the only option for more accurate CCM analyses was to implement a methodology regarding how to efficiently use low-detail elevation models. The usability of these models can be achieved by adjusting the maximum slope limits for a passable terrain. A hardly passable terrain can be considered impassable in low-detail models. To obtain similar results for the area of passability as high-detail elevation models, adjustments in Table 5 had to be performed. These adjustments need to be applied to elevation models based on the traction parameters of a vehicle (maximum reachable slope), which were calculated from traction curves or the DMA (Defence Mapping Agency) model; for details, see [16]. The values in Table 5 were calculated from the mean slope values of elevation models for each slope class (see Table 3). Afterwards, these values had to be modified according to the results of CCM map analyses, displayed in Tables 4 and 6 and as map results in Figures 8-10. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**GO or SLOW GO** & \multicolumn{3}{c}{**Reduced Slope Values (\({}^{\circ}\))**} \\ \cline{2-4}
**Slope Value (\({}^{\circ}\))** & **DTM 4** & **DTM 3** & **DTED 2** \\ \hline
10 & 9.9 & 9.6 & 9.3 \\
15 & 14.5 & 13.4 & 12.8 \\
20 & 19.0 & 17.3 & 16.4 \\
25 & 23.5 & 21.2 & 19.8 \\
30 & 27.8 & 25.1 & 23.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Adjustments of maximum slope value reachable by a vehicle for passable (GO) and hardly passable terrain (SLOW GO) that were needed to achieve more accurate results for CCM analyses. Modifications calculated for DTM 4 (5 m \(\times\) 5 m), DTM 3 (10 m \(\times\) 10 m) and DTED 2 (30 m \(\times\) 30 m). If a calculated maximum reachable slope for a hardly passable terrain (SLOW GO) for a vehicle was, for example, 25\({}^{\circ}\), then by using the 10 m \(\times\) 10 m elevation model, the maximum reachable slope was only 21.2\({}^{\circ}\) and the CCM analysis map should be adjusted. DTM 5 served as the most accurate model database to calculate the slope deviations of other elevation models from the real terrain. DTM 5 is a very accurate model (1 m \(\times\) 1 m) but still deviates from the real terrain. Given the trends of lower-detail models displayed in Table 5, the estimated maximum reachable slope value reductions for DTM 5 would be 0.2\({}^{\circ}\) for 20\({}^{\circ}\) slopes, 0.5\({}^{\circ}\) for 30\({}^{\circ}\) slopes and 1.5\({}^{\circ}\) for 45\({}^{\circ}\) slopes. The accuracy of slope reductions was tested for a different extent and conditions. The tests were performed in the form of CCM map analysis in a 3 km \(\times\) 3 km area in Dolni Morava (arid and moist conditions), a 6 km \(\times\) 6 km area in Kdynne (moist conditions) and five combined selected areas of 5 km \(\times\) 5 km (moist conditions). The main comparative characteristics were variations of passable/impassable area between corrected models and models not corrected. The other characteristic was a comparison of the position of a hardly passable and impassable terrain. The results with the calculated slope reductions (Table 5) were more accurate and were markedly closer in position to the most detailed elevation model, namely, DTM 5, than results without slope reductions (see Tables 6-9). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & **DTM 5** & **DTM 4** & **DTM 3** & **DTED 2** \\  & & **Area (\%)** & **Area (\%)** & **Area (\%)** & **Area (\%)** \\ \hline \multirow{3}{*}{No slope corrections} & GO & 72.01 & 73.17 & 74.44 & 73.04 \\  & SLOW GO & 24.71 & 24.70 & 24.40 & 26.07 \\  & NO GO & 3.28 & **2.13** & **1.15** & **0.90** \\ \hline \multirow{3}{*}{With slope corrections} & GO & 72.01 & 72.65 & 72.06 & 69.19 \\  & SLOW GO & 24.71 & 24.35 & 24.77 & 26.59 \\ \cline{1-1}  & NO GO & 3.28 & **3.00** & **3.17** & **4.23** \\ \hline \hline \end{tabular}
\end{table}