Notes on time-of-flight for Odin

Some notes to clarify the use of pixel positions for imaging instruments:

The imaging detectors at Odin (and TBL) will function differently from most of the other detectors.
We don't really have pixel positions for the actualy detector, because it is a scintillator which is recording the neutrons, and converting them to photons that the cameras can then see.
The photons travel from the scintillator through lenses and other optics, before they reach the camera.

This means that the positions of the camera pixels are in fact irrelevant for computing tof, as the camera can be placed meters away from the scintillator. What matters is when the neutrons were detected by the scintillator.
This is why we need the flight path calibration.

It is meant to build a Ltotal as a function of pixel_id, or coarse group of pixels.
We can also envisage using a kernel/window averaging over the detector pixels to get a smoother Ltotal distribution function.

No file, test, or entry point is named. Start by locating the Odin and TBL time-of-flight or flight-path calibration code, then compare how detector pixel positions are currently used. Done should establish how calibration produces Ltotal by pixel_id or coarse pixel groups, including any intended smoothing window.