add test for recipe localization modules coordinate conventions - #1663

Coordinates in general could use a bit of a work-over - it's a bit more than just nm vs pixels, it's nm (roi referenced), nm (origin referenced), or pixels. Pixels is the most forgiving if the data comes from a source where it might be missing some metadata , but is also the least powerful.

I wonder about adding some sort of units awareness to tabular, and letting it handle conversions (so if you had a column x, you could query e.g. x_nm or x_pixels), but this could be adding complexity where it's not needed.

I do think baking in more unit awareness would be helpful rather than harmful. For example the change to have voxelsize_nm instead of just assuming voxelsize.x is in um has been quite nice.

Separately, I wonder whether there are other ways to bring DetectPoints2D into alignment with the FitPoints module - right now it is super frustrating to e.g. develop a recipe using localization, do the flat fielding yourself etc. and then if you forget to roll your own mapping filter (which is tough because you have to add voxelsize_nm to the mapping namespace somehow or magic number it), you end up with a major bug.

Having a bit of a think about what we'd really need to make this work in tabular.

To be robust we'd need to track:

type: (initially, None or "coordinate" / position)
units: (pixels, nm)
origin: (camera, ROI, stage, other?)
applied transformations: (has this been re-mapped from an image-splitting devce, or drift correction etc ...)

This feels quite heavy for the tabular class when it applies to 3 columns but not to others.

Serialising to hdf will be fine (or rather we can find a way to make it work), serialising to csv / excel will loose all the metadata.

I'm not saying we shouldn't do it, but just that we should think a bit about how.

One possible approach (albeit with high breaking change potential) is to actually change anything that currently writes x to write e.g. x_cam_pixels, x_roi_pixels, x_roi_nm instead and to implement a light-weight wrapper that does backwards compatible translation to x (advantage of this is that the unit intent is not lost if writing to e.g. csv, even if the metadata needed to translate the units is). Asking specifically for x_roi_pixels (rather than x) in a downstream module will fail in a fairly explainable way if that can't be computed.