The USGS DEM standard is a geospatial file format for storing a raster-based digital elevation model.
Pix4Dmapper generates the raster DSM in .geoTIFF format. To export it to .dem:
1. Open Global Mapper.
2. Import the Pix4Dmapper DSM (.geoTIFF).
3. From the Menu: File > Export > Export Elevation Grid Format.
4. Select the DEM format.
For more information: http://www.globalmapper.com/
Disclaimer: Pix4D publishes this information as a courtesy to its customers. Pix4D makes no warranty of any kind, expressed or implied, with respect to the content's validity or accuracy.