A Digital Elevation Model (DEM) is a grid of regularly spaced cells with a height value in each cell. It is suitable for defining 2.5D surfaces.
You can think of the gridded DEM being directly related to the orthophoto. They are based on the same projection plane. The orthophoto has an RGB color per cell, and the DEM has a height per cell. Exported DEMs can also have full geographic information to place them accurately in the world.
DEMs can be exported as sparse XYZ text files, or as GeoTIFF files (16-bit integer or 32-bit float). Several applications such as ArcGIS, GlobalMapper, QGIS, 4dmapper.com, and Google Earth can import PhotoModeler’s DEM and orthophoto products.
The DEM is created at the same time as the orthophoto with a small variation to the user-given file name (XYZ files are given the same root file name as the orthophoto but with the .xyz extension; GeoTIFF files are given the same root file name but with .DEM.tif as the extension).
To create a DEM from the project’s terrain elevation data, select the File type of the final result, and the sample rate. If the file type is ‘None’ (the default), no DEM is created. The sample rate defines the relationship to the orthophoto. For example, “DEM sample every orthophoto pixel” outputs a DEM with the same number of cells as the orthophoto. If the orthophoto was 640 by 500 pixels, the DEM would also be 640x500. Note the GeoTIFF versions are images and so will have same number of pixels as the orthophoto, but the XYZ file is sparse (not containing any data where there was no surface data in the project). XYZ file order is also not defined. Often the DEM does not need to be the resolution as the orthophoto, so the DEM sample setting allows every 2nd, 3rd pixel, etc. That 640 by 500 orthophoto with ‘every second orthophoto pixel’, would result in a DEM of 320 by 250 grid cells. XYZ files do not have projection or other geo-data that GeoTIFF files do, but you can export a world file.
These options are only enabled in the PhotoModeler Premium version.