Heterogeneous spatial scales

[azaroth42]

Currently it is only possible to represent a single ratio for scaling the unit lengths of canvases or scenes into physical dimensions. There are use cases, such as some X-Rays or some images that are intentionally deformed along a single axis (map warping), in which the unit scales are different.

These are currently considered out of scope for Presentation 4.0, but if there are specific instances where this would be useful, then please make a comment on this issue.

The suggestion from the editors would be to have an extension that defines spatialScaleX, spatialScaleY, and spatialScaleZ, which should not be provided at the same time as the spec-defined spatialScale.

[JulieWinchester]

Possibly would enable CT DICOM use cases, which are not common even in CT, but e.g. the 2-dimensional pixel spacing present in https://dicom.innolitics.com/ciods/rt-dose/image-plane/00280030