FOCUSZ is not currently in ExposureInfo. We want to add this in so we can access it with the images along with the unit information. As I understand it this requires two steps:
1) Add the focus_z information into ObservationInfo in astro_metadata_translator.
2) Then it can be added to ExposureInfo.
Questions I have:
Should it go into VisitInfo?
How can you add distance units to values in the C++? I see you can use the lsst.geom units for angular things but not sure about linear distance.