Converting Multiple OSM Files to a Single ODB File for Large Urban Databases - Virtual Flight Test
Virtual flight test simulations are conducted to understand the flight dynamics in terms of radio propagation and to design an efficient communication network. The very first step to perform such tests is to create an urban database that contains the topography as well as the building and vegetation infrastructure. One of the techniques used to create such an urban infrastructure is to use the open-source maps such as open street maps (OSM) and obtain the map of the terrain that contains buildings with different heights as polygons and the vegetation information.
Since OSM is an open-source platform, it does not allow an area larger than 50,000 nodes to be downloaded. So, in order to create databases that are large, one needs to carefully download the maps so it can be merged without losing much information. This workflow is specifically used for creating large urban databases with multiple osm files. In this example, a map which has the Altair World headquarters at Troy in the center (42°33'41.8"N 83°06'42.5"W) with urban infrastructure around it for a radius of 2 miles is chosen for the database as shown in Fig 1
Fig 1. The urban area around the headquarters that is of interest for the modelling.
Since this area is larger than 50,000 nodes, one cannot download the complete map from OSM in one iteration. So, this must be broken up into a minimum of two iterations. The easiest way to do this is to keep either the latitude or the longitude fixed and by splitting the other equally into two halves. For example, the 1st iteration could be of the area [42.60 N, 83.13 W] to [42.52 N, 83.10 W] and the 2nd iteration could be of area [42.60 N, 83.10 W] to [42.52 N, 83.07 W]. In this case the latitudes are fixed, and longitudes are split. By doing so, one can obtain two areas lesser than 50,000 nodes and can be downloaded as two different maps as shown in Fig 2 & 3. (Please see the attachments for map1.odb (iteration area #1) and map2.odb (iteration area #2).
Fig 2. Area for Iteration # 1.
Fig 3. Area for Iteration # 2.
The next step to complete the urban database is to convert both the .osm maps into a vector database (.odb) files and combine them together by importing them one after the other. While conversion, it is important to note that the coordinates information will also be stored as part of the .odb file and hence always use UTM zone automatically determined to do this as shown in Fig 4.
Fig 4. Settings for importing the .osm map for .odb conversion.
This will convert the Geodetic coordinates of the map to UTM coordinates and this step ensures that when two such converted odb files are imported one after the other, there is no need for including an additional offset or by manually defining the location for the imported map. One can leave the move vector to default x, y, and z as 0 as shown in Fig 5.
Fig 5. Move vector when importing map2.odb.
The final imported map (map1 + map2) is attached as AltairHQ.odb and can be seen in Fig 6. The 3D view of the section of the map around the Altair HQ’s is seen in Fig 7. Using this approach, one can generate large databases by splitting the area into well defined smaller areas (with fixed latitude or longitude) and convert them to .odb files. Once this process is completed, one can import them in the order it was created one after the other without any offset to realize the final urban database.
Fig 6. The final combined urban database that includes both maps 1 & 2. (Altair HQ in red)
Fig 7. A 3D view of the section of the map with Altair HQ.