Incorrect auto-converted glTF scale

Development and API
#1

When downloading an auto-converted glTF model, the scale is incorrect. It doesn’t look like the Sketchfab glTF exporter uses the FBX scale factor correctly. This problem is also not limited to the auto-converted FBX files.

I’m a member of the Mozilla Hubs team and we’re currently using the download API in Hubs and our editor Spoke. When our users use assets from Sketchfab in Spoke they need to scale most FBX assets to 0.01. This suggests that the FBX to glTF conversion is not handling converting from centimeters to meters. glTF specifies that it’s units should be in meters, so it would be great if the auto-converter would convert to meters whenever the original file format has information describing its units.

IMO Sketchfab has the best and biggest repository of glTF assets out there, thank you so much for all that you do!

#2

Thanks! Our 3D team will take a look. There’s not really any notion of scale in the Sketchfab viewer, so I wouldn’t be surprised if we are missing a cm to m conversion.

1 Like
#3

Awesome, thanks for taking a look at it!

#4

Hi,

As @james said, our processing doesn’t really take care of the scale for now, so the lack comes from FBX processing (as glTF export doesn’t alter data).
The reason is that It didn’t really make sense (initially for Sketchfab) for models viewing since the viewer didn’t have any notion of scale and there have not been real usecases of this.

Now, and since models are available through the download API, we are aware that having the right scale makes much more sense, as it makes it easier to download and directly import models with the right scale into an existing scene.
We will discuss this topic and see what can be done to improve glTF download workflows :slight_smile:

Thanks for reporting!

4 Likes
#5

That sounds great, thank you!

#6

@waleguene is there an update on this? I’m using some of your models and noticing the similar issue around scale. Could we at least assume the unit of the measurement in the GLTF model to be either cm or m?

#7

There is an ongoing discussion about this as it’s an important topic for AR purposes, but nothing done yet.

glTF defines distance unit as meters, but it’s still not guaranteed to be respected with existing models.
There have been no effort yet on the scale consistency in FBX or any other format allowing to store this data (and also not sure artitsts would take care of setting it correctly)

The only thing I can tell for now is that some efforts will be done on this topic in the incoming weeks :slight_smile:

1 Like