With OziExplorer the DEM files are never fully loaded into memory, OziExplorer uses a method of indexing, pre-calculating and caching to extract the required elevation from the dem file in the quickest possible time.
The DEM files are placed in the folder that has been specified for the type of dem.
When OziExplorer is started (or the Elevation Configuration is saved) the DEM File Paths are scanned (if set as active), sub-folders attached to these paths are also included in the scan. If a file called default.ozproj is found in the folder the grid and datum are read from it and used for each DEM in the folder. As the DEM files are scanned the details about each dem are stored in memory.
When an elevation is required the most suitable DEM is selected and the elevation is read from the file.
If many types of DEM's are active OziExplorer selects the DEM to use in this order.
Example - if a USA Dem 24K and Gtopo30 data exist and are set as active, the USA Dem 24K data will always be used.
Within each type of DEM type the file with the best horizontal resolution of data points is used
If you have a large number of dem files it may become too slow to scan them all, it is therefore suggested you divide them into regions and set the paths to point to a region of interest.
Some dem types are indexed and this produces an extra file called .ozline. If the .ozline file does not exist it is created the first time the dem is scanned. The creation of the .ozline file can take a few minutes but only has to be done once. The .ozline files can be deleted at any time, if required they will be created the next time the dem is scanned.
If Use Elevation Data is active and elevation data is available and you are using waypoints or tracks for any purpose, such as Track Profile, sending to OziExplorer3D and so on, then if the data does not include elevations then they are automatically used from the DEM files as required.
When a 3D map is being created OziExplorer divides the map into a grid using the specified grid spacing, it then obtains an elevation for each of the grid points (using interpolation with filtering if specified). The height data is written to the .3d1 file together with any other information required by OziExplorer3D, the file is then passed to OziExplorer3D for display.