By Garry Stockton
Image courtesy of Autodesk
NWD File Format
When you save to a NWD (Navisworks file), all loaded models, the environment, current view and saved viewpoints (including redlines, comments etc) are all saved to a single file. This is known as publishing a Navisworks file and creates a ‘snapshot’ of the project file/data. An NWD file is considered the complete file and can be opened in any Navisworks product and the Navisworks Freedom viewer. However, when you publish an NWD, you can specify metadata to be saved in the NWD, choose whether to omit model data from the NWD, add password protection, set an expiry date and most importantly make the NWD read-only so that it cannot be modified and resaved or even included in another NWD file.
NWF File Format
When you save to the NWF (Navisworks file format), you get a list with pointers to the files that are currently loaded and saved, along with the scene's environment, current view, clash results, and saved viewpoints (including redlines and comments).
To open an NWF file, a Navisworks product is required, such as Manage (not Freedom), as well as access to the original CAD files. (Note: Copies of the original CAD files may be used, however they must have the same file names as the original CAD files).
When you open an AutoCAD or Revit file in Navisworks, by default, a cache file (NWC) is created, which contains all the converted details required. When you subsequently open that CAD file in Navisworks, it will check to see if a cache file is available. If it is, Navisworks will check to see if the CAD file has been modified since it was last opened in Navisworks. If the file has not been modified, Navisworks will read the cache file, this speeds up the loading process and uses less memory. If the CAD file has been modified, Navisworks will read the CAD file in again and re-create the cache.
It is strongly recommended that you use an NWF file when referencing several CAD files. This will prevent you from having to republish the Navisworks file whenever one of the CAD files is amended, because the NWF file will open the most recent files available. The NWF file will read in the cache files of CAD files that have not been modified, which will reduce the time to load the files and the amount of memory used.
I would also recommend that you use an NWF file when conducting clash tests. The original clash results will be saved in the NWF file. You can then update the CAD files as necessary. When the NWF file is opened again, the revised CAD files will be opened, and the Clash Detective, having retained the original clash data, will check that those clashes have already been resolved.
I hope you find this useful