# The Influence of the Quality of Digital Elevation Data on the Modelling of Terrain Vehicle Movement
## 4 Discussion
### Recommendations for Improvements of Elevation Models  
The introduced method of slope reduction for the usability of low detail elevation models in CCM analyses was affirmed as correct. All results showed an improvement in the accuracy of passable areas, both in extent and position (as shown by the Figure 10 map comparisons and Tables 6-9 numbers in bold). However, the size and number of testing areas were limited. Verifying this concept at a global scale would require extensive data testing in large areas across Europe, Asia and Africa for various elevation data sources. The key element is also a focus on specific restricted areas for passability. These are hilly and mountain areas, where a key slope limit of approximately 30\({}^{\circ}\) occurs more often than in other types of terrain. Additional testing sites should make the slope reduction values presented in Table 5 more accurate. Further slope adjustments to the values in Table 5 would probably only be minor. Global detailed data readiness is something that NATO currently lacks. The usability of digital terrain models is not limited to only high-detail models. NATO can use low-resolution models in foreign operations in a time frame before any detailed elevation data is procured, e.g., LIDAR data. Low-detail elevation models can fulfil this aim via the additional processing of data introduced in this chapter using the method of slope reduction. Accurate CCM analyses cannot be achieved without including microrelief forms in the analysis. DTM 5 (1 m \(\times\) 1 m) consists of all microrelief objects, for example, embankments. The other elevation models mostly do not consist of these objects. Remedy can be achieved with vector data that consists of roads and other line or point objects that are important for passability. These objects could be incorporated into analyses with low-detail elevation models as impassable obstacles. The current ongoing project of the global vector database MGCP can serve as a source of information for objects on the terrain. Nowadays, expectations for improvements in global elevation models are focused on the TREx project. TREx is a surface model; therefore, its usage for accurate CCM analyses is limited. Nevertheless, new methods for processing TREx data into the form of a digital terrain model are currently in development. Although this might make a new global digital elevation model with a resolution of 12 m \(\times\) 12 m available, the accuracy of altitude of areas formerly consisting of forest and built-up areas is low. The reason for this is that data from these locations are interpolated from lower detail models, e.g., DTED 2. TREx is also available in its raw unprocessed form as a cloud of points. Using this data can allow for rapid reaction analyses for any crisis region across the world. The disadvantage is in more complicated processing, mostly because of the overly large data volume. So far, no global elevation model has met all requirements needed for accurate CCM analyses. Global coverage with ready-to-use data is the highest priority. The second priority is the detail of an elevation model, which ideally should be 5 m \(\times\) 5 m. The surface model, such as TREx, is not a sufficient replacement for a regular digital terrain model. For the moment, the only possible solution for this would be the use of automated systems fitted on military vehicles that evaluate passability parameters in real time. Even though the capability of automated navigation of military vehicles is not widespread in NATO, the systems will become the future of CCM modelling. To compare the influence of the use of different elevation models on the determination of terrain passability, different statistical methods can be used. The use of the parametric ANOVA method would be possible under the assumption of a normal distribution of data. However, this distribution does not occur in the event of extreme changes in the terrain, e.g., changes in adhesion due to precipitation.