Wrl scaling question

I notice that when KiCad 3D viewer reads wrl files, it interprets a unit of 1 in the wrl as 0.1-inch in PCB space. This is with KiCad Footprint Properties > 3D scaling set to 1.

Is that a fixed setting? Is there some rational for that setting?

(Obviously I can set KiCad’s 3D scale to something else. I’m just trying to understand the “native” scaling relative to wrl units, and why it wasn’t just 1:1)

Thanks, Graham

Whomever recently posted a link about StepUp deserves the credit for this link:
KiCad 3D Models

^ The STEP file format includes model scaling information, and so the 3D model scaling parameter must always be set to 1:1 in mm

^ The WRL file format does not specify absolute dimensions. KiCad normalizes model parameters to units of Inches, and the internal units of the WRL files should be scaled accordingly

Sorry that I don’t remember who provided this link recently to give proper credit.

Nominally, WRL units are 1 unit = 1 m, since the format was designed for virtual reality environments (WRL = World), this was a convenient scale. However, people routinely abuse the standard and pick whatever unit is convenient to them, which is likely if they use the format outside it’s intended purpose.

KiCad chose 1 unit = 0.1 inch, which possibly made sense when PCBs mainly contained DIP packages with 0.1" spacing. The scaling is fixed, there is no option in the WRL to specify different units.

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Thanks bobc. Your rationale for KiCad interpreting 1 wrl unit = 0.1inch makes a lot of sense.