Topography of an area is an important factor that needs to be accounted for when performing land to air communication or vice versa. The elevation data is also vital for understanding the dynamics of a virtual flight network planning. The first step in performing such simulations is to create a map that encompasses the region under test with vector data for buildings and vegetation. Once this is completed, the topography or elevation information of the region should also be included as a form of pixel database. One of the ways to obtain such pixelated elevation database of any region is from the United States Geological Survey website (USGS : https://earthexplorer.usgs.gov/).
The USGS provides free elevation data for any region on the globe. The minimum area it can provide is a 1 degree * 1 degree (Perimeter = 2’ latitude + 2’ longitude). Sometimes, this area can be several states or even countries depending on the location. In this workflow, it is shown how to extract pixelated elevation data from USGS and downsize (crop) it to the region that is under study and upload it as part of the urban database along with the vector data for buildings and vegetation to complete the simulation map.
For example, if one requires the elevation information of the area around our Altair Global Headquarters (42°33'41.8"N 83°06'42.5"W) as seen in Fig 1 then first, the region of interest, which is a 2-mile radius around this location from [42.60 N, 83.13 W] to [42.52 N, 83.07 W] should be defined.
Fig 1. USGS website interface showing Altair HQs.
For defining the region, the next step is to enter the coordinates to download the elevation data. The coordinates can entered either in degree, minute, & second format or the decimal format as shown in Fig 2.
Fig 2. The area of interest defined (decimal format) for which the elevation data is required.
The third step is to download the elevation data by choosing the SRTM 1 Arc-Second Global digital elevation data set as shown in Fig 3 and proceeding to download the result dataset in DTED format (coordinates 42,-84) as shown in Fig 4.
Fig 3. Selection of appropriate dataset to represent digital elevation pixel data.
Fig 4. Final dataset from the USGS database.
The fourth step is to convert the downloaded DTED database into the topographical data base so this can be made part of the urban database with the vectors for building and vegetation as shown in Fig 5. The choice of conversion should be in Geodetic coordinates as this is essential for editing it in case the database is larger than the interested region. After performing the conversion in WallMan, editing the database should be done in ProMan. The unedited topographical data is shown in Fig 6 (see attached Altair_HQ_Full_Topography.tbd).
Fig 5. Converting digital elevation data to topographical database.
Fig 6. The unedited topographical data.
The next step is to edit the database and crop it to the region of interest (2-mile radius around the Altair HQ). It is always best to add an additional offset of 0.2 degrees to the bounds of the database to make sure that the offset from the OSM maps is also accommodated within bounds of the elevation database. The database bounds for this example are entered as shown in Fig 7. This can be performed under extract data tab in the edit menu.
Fig 7. Modified bounds of the elevation database.
Once the bounds are defined, the database is cropped to the bounds and it can be saved to be used for the urban database with vector data of building and vegetation (See attached Altiar_HQ_Modified_Topography.tdb). The last step before importing the modified elevation data into the urban database is to check if the format of the coordinates of the urban database and the elevation database matches. In this case, the urban database is in UTM format and the elevation database is in Geodetic format. So the elevation database must be converted to UTM format as shown in Fig 8.
Fig 8. Converting elevation database into UTM format.
After conversion, the final step is to import both the vector database with building and vegetation data and the elevation database as shown in Fig 9 and the 3D view is shown in Fig 10. (See attached AltairHQ_withelevation.odb)
Fig 9. The completed database that includes the buildings, vegetation, and the elevation data around Altair HQ.
Fig 10. 3D view of the final database.
