To what point on a volume does the the three vector (0,0,0) point? I could imagine that it would be the mid-point on a regularly shaped volume but have not seen that explicitly stated. What about irregular shapes? I have been unable to find this explained after searching around on the geant4 forum.

That should be documented in the Application Developers Guide. In particular, all “regular solids” are defined in terms of “half dimensions”, such that their local coordinate system extends from -x/2 to +x/2 along each axis.

More complex solids, such as `G4Polyhedra`

, have coordinate bounds defined by the user, so that the origin (0,0,0) is wherever the user has chosen it.

You can see the origin of coordinates:

- for the world with
`/vis/scene/add/axes`

; - for a particular solid with
`/vis/drawLogicalVolume <logical-volume-name>`

.