Inconsistent behavior of pixdim in Spacing

[ChenglongWang]

Recently, I noticed that the pixdim argument from the Spacing transform is inconsistent with other transforms.
For the pixdim in Spacing transform, if providing a single number, will use it for the first dimension. items of the pixdim sequence map to the spatial dimensions of input image. However, for the most of other transforms, such as Resize, SpatialPad, and BorderPad, single number argment will be automatically filled to the image size by using fall_back_tuple fn.
I'm wondering why Spacing transform is designed this way. Will this inconsistency lead to any improper usage?

[wyli]

thanks, I'll create a feature request from this, defaulting to the isotropic resolutions instead of all 1.0 values, though I'm not sure which one is better...

[ChenglongWang]

Hi @wyli , thanks for your quick response

I think isotropic resolution is more natural behavior for the single number input to keep consistent with other transforms.
If users need 1.0 value, I think most MONAI users will naturally input (x, 1.0, 1.0).

[wyli]

(addressed by #5248)