This file contains the end point coordinates of the segments forming the edges of the solids defined in the geometry file. The columns of the SDDS file are xFrom, yFrom, zFrom, xTo, yTo, and zTo. If two regions with the same material are touching, then the common edge, if any, is not included.
The commandline option -vacuumStep=<distanceInCM> allows one to change the default distance by which particles are tracked at every step in vacuum regions. In vacuum, all particles have infinite mean-free path. For cpu efficiency, the default is made a very large number such as 10 m. To create coordinates inside vacuum regions, a distance value smaller than the dimension of the regions must be given.