So here is the skull.babylon file in the sandbox viewer :
And here it the same model, after I use the sandbox viewer to export it in gldb and then reopened in the sandbox.
It appears that the z(blue) axis is facing the “wrong” direction. What gives ?
How to use blender to change this ?
I think this is the main reason I face some problems with the models orientation and which face it uses to lookAt() something.
I think its due to axys conventions which are not the same between BJS and glTF.
That said, to “clean” a model in Blender, apply transforms (3DView > Object > Apply), especially rotation here.
In a particular case where you want modify the origin rotation, the only way I found without using addon is to create a primitive (in object mode, not edit) using the Align View option in the Redo Last popup, having previously align your viewport ortho view using face selection. Then merge your model to the primitive.
This happens when I apply all transforms. It seems that the origin got transferred.
I don’t understand well what to do after. Also can I use the addon you mentioned to make it quicker ?
Maybe unparenting before apply transforms is necessary. About addon I don’t know one, I mentionned that 'cause I suppose someone already code this kind of functionnality.
Actually I learned a bit more about Blender and I just messed arround with the model in EDIT MODE instead and rotated it.
Thanks for the fast answer cause I’m losing my mind with this thing 
