Needed: Parameter group to specify the initial position and orientation at the beginning of a branch (or any other element).

[DavidSagan]

Group specifies the floor position. This group can also be used to hold the (calculated) floor position of any element.

[mattsignorelli]

I think this would just go in a branch struct directly instead rather than a new parameter group. Similarly can have deferred construction if you want to specify it in an element (like fiducial) as we do now with InitialBeamlineParams

[mattsignorelli]

floor position will be virtual parameter computed similar to how s is computed

[DavidSagan]

OK we should talk about this. The important thing is for the user to be able to set the floor position for any element (not just at the beginning). Storing at the Branch level (I'm using the naming convention of PR #137) would not be feasible since a branch may have multiple elements that set the floor position (see, for example, the floor_position element in Bmad). Storing at the Beamline level is possible as long as multiple Beamlines are used for a Branch with multiple floor position sets.