Specifically, it finds BSP nodes with dividing planes where Tool has incorrectly assumed that one side is "outside" the map and reuses the same child node for both sides of the failed node.
Ghostbuster is built on the Reclaimer library.
You will need Python 3 to use this tool. Clone the repository from GitHub, or download
requirements.txt somewhere convenient. Install dependencies with
pip install --user -r requirements.txt.
Ghostbuster modifies BSP tags in-place unless the
-dryrun flag is added, so it is recommended to first backup the tag if it cannot be recompiled easily. From a command line:
python3 ghostbuster.py <path to BSP tag>
Due to rounding errors and the nature of how phantom BSP are detected, the script may report and "fix" a large number of false positives or miss some phantom BSP. This is not usually detrimental to the map, but it has been reported to cause a collision error in one case.
Using Ghostbuster should be a tool of last resort, and phantom BSP can usually be cleared up by adjusting nearby geometry and fixing nearly coplanar faces indicated in the WRL file.