Choice of default model units in Voyager

[sdumetz]

Voyager uses cm as the default unit for scenes and models. I was wondering why?

glTF models are unit-less but if I recall correctly, they are generally implicitely in meters. Blender certainly seems to consider meters to be the default.

It's of no importance for scene creation, where you can select (or force) any unit you want in the initial schema, but it gets really annoying when we import new models to an existing scene and their scale is always off by a factor of 100.

Is the use of centimeters required by some internal Smithsonian processes? or deemed preferable for some reason? Is it something that we might consider changing?

Code-wise, changing the default unit for newly created models is just one line in CVModel2.ts:L92:

        localUnits: types.Enum("Model.LocalUnits", EUnitType, EUnitType.cm),

[gjcope]

Hi @sdumetz,

Per the glTF specification they are supposed to be meters but, of course, in practice that often doesn't happen.

I don't know the history of that default choice, but I believe it has more to do with display units than local units. The majority of the things we digitize would fall into the size category that is appropriately measured in cm. And having a one-to-one with the local units makes it easier to adjust things if needed. Regardless of the default there will always be adjustments needed, but it's a fair point that our primary model type is supposed to be in meters. I will bring it up on my end and see what others' thoughts are about changing.

[sdumetz]

I think using cm for scene units is as good a default as any. The "best" unit there will always be relative to the subject's size in any case.

But I'd be interested to know if some/most of your models are exported with cm scale or if like us your scene creation workflow always overrides the default to meters; but the inconsistency doesn't surface unless you're uploading a new model to the scene. In which case, the default ModelUnit should probably be changed.