# The Influence of the Quality of Digital Elevation Data on the Modelling of Terrain Vehicle Movement
## 3 Results
### Comparison of the Accuracy of Slopes Derived from Digital Terrain Models
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multicolumn{2}{c}{**Slope Classes**} & \multicolumn{4}{c}{**Mean Slope (\({}^{\circ}\))**} & \multicolumn{4}{c}{**Mean Slope Difference from DTM 5 (\({}^{\circ}\))**} \\ \hline
**Quantity** & **Slope** & **DTM 5** & **DTM 4** & **DTM 3** & **DTED 2** & **DTM 4** & **DTM 3** & **DTED 2** \\ \hline
10,134 & 0–5\({}^{\circ}\) & 3.14 & 4.09 & 5.21 & 5.17 & 0.95 & 2.07 & 2.02 \\
12,389 & 5–10\({}^{\circ}\) & 7.17 & 7.28 & 7.54 & 6.82 & 0.11 & 0.37 & \(-\)0.35 \\
6946 & 10–15\({}^{\circ}\) & 12.37 & 12.07 & 11.74 & 9.94 & \(-\)0.30 & \(-\)0.62 & \(-\)2.43 \\
5933 & 15–20\({}^{\circ}\) & 17.45 & 16.59 & 15.42 & 12.59 & \(-\)0.87 & \(-\)2.03 & \(-\)4.86 \\
5696 & 20–25\({}^{\circ}\) & 22.49 & 21.41 & 19.11 & 15.85 & \(-\)1.08 & \(-\)3.39 & \(-\)6.64 \\
4987 & 25–30\({}^{\circ}\) & 27.38 & 26.05 & 22.37 & 18.09 & \(-\)1.33 & \(-\)5.01 & \(-\)9.29 \\
2679 & 30–35\({}^{\circ}\) & 32.10 & 29.81 & 23.37 & 18.33 & \(-\)2.29 & \(-\)8.72 & \(-\)13.77 \\
740 & 35–40\({}^{\circ}\) & 36.95 & 31.24 & 22.80 & 15.75 & \(-\)5.72 & \(-\)14.15 & \(-\)21.20 \\
191 & 40–45\({}^{\circ}\) & 42.00 & 33.36 & 22.64 & 14.23 & \(-\)8.64 & \(-\)19.36 & \(-\)27.77 \\
96 & 45–50\({}^{\circ}\) & 47.41 & 37.25 & 26.36 & 10.48 & \(-\)10.16 & \(-\)21.05 & \(-\)36.93 \\
54 & 50–55\({}^{\circ}\) & 52.53 & 40.48 & 28.51 & 8.73 & \(-\)12.05 & \(-\)24.02 & \(-\)43.80 \\
55 & 55–60\({}^{\circ}\) & 57.48 & 46.31 & 30.92 & 6.90 & \(-\)11.17 & \(-\)26.56 & \(-\)50.58 \\
41 & 60–65\({}^{\circ}\) & 62.82 & 48.48 & 26.30 & 5.42 & \(-\)14.34 & \(-\)36.51 & \(-\)57.39 \\
35 & 65–70\({}^{\circ}\) & 67.43 & 51.05 & 31.97 & 5.80 & \(-\)16.38 & \(-\)35.46 & \(-\)61.63 \\ \hline
50,000 & Total & 14.27 & 13.77 & 12.64 & 10.54 & \(-\)0.50 & \(-\)1.63 & \(-\)3.73 \\ \hline \end{tabular}
\end{table} 
Table 3: A comparison of slopes in random points generated from elevation models and their statistics. Figure 3: Histogram of standard deviations of the comparison between DTM 3 and DTM 5 for slopes at 50,000 points. Figure 2: Histogram of standard deviations of the comparison between DTM 4 and DTM 5 for slopes at 50,000 points. Figure 4: Histogram of standard deviations of comparison between DTED 2 with DTM 5 for slopes at 50,000 points. Figure 5: Graph comparing mean slope values of different terrain models (DTM 5, DTM 4, DTM 3, DTED 2) at identical points. Slope classes were determined from DTM 5. The assessment of the specific slope values and digital terrain models resulting from the analysis of Figures 2-7 is given below. Evaluation of specific slope values (slope classes):  
Low-detail elevation models did not differ from high-detail ones for lower slope values (slope values were very similar). The basic threshold was up to 10\({}^{\circ}\) for lower-detailed models (10-30 m) and up to 30\({}^{\circ}\) for medium-detailed models (5 m). Slopes up to 5\({}^{\circ}\)--The average slope value was higher in all tested models than in DTM 5. More detailed terrain models (DTM 5) had a more gradual slope in the lowest class. This inversed effect was specifically found in the flat areas only. Slopes 5-10\({}^{\circ}\)--The average values of slopes were very close for all models and the standard deviations were not very high either. It is possible to use less-detailed models in terrain analyses for slopes up to 10\({}^{\circ}\). Figure 6: Graph comparing the mean variance of slopes of different terrain models (DTM 5, DTM 4, DTM 3, DTED 2) at identical points. Slope classes were determined from DTM 5. Figure 7: Graph comparing standard deviations of slopes of different terrain models (DTM 5, DTM 4, DTM 3, DTED 2) at identical points. Slope classes were determined from DTM 5. Slopes 10-30\({}^{\circ}\)--Almost a linear increase in slope could be observed depending on the resolution of a model. The average deviations with DTM 5 also had a linear increase. The more detailed the model, the greater the proportion of higher slopes. This slope class was still relatively reliable in all models (except DTED 2).