How to export .gltf with a different unit

[ghsoares]

When working with assemblies, GLTF can be a export option, it's better to preserve a tree-like hierarchy, when exporting multiple parts in the same file, for example.
While the STL file format is unitless, gltf file format is explicitely defined in meters.
The main problem I have is that when I model using millimeters as units, exporting to GLTF results into huge meshes.
When exporting as STEP file, I can provide the internal model units and the output units, I was wondering if there is a way to do the same thing when exporting to GLTF, or at least a way to scale up/down the final assembly, while maintaining the tree-like hierarchy.

[mohsensc]

assy.export() doesn't take a unit option for glTF. exportGLTF hands the tessellated doc straight to OCCT's RWGltf_CafWriter with your mm values as-is (assembly.py). The writer can convert though, you just have to tell its coordinate converter what unit the input is in. Copy of exportGLTF with one extra line:

from cadquery.occ_impl.exporters.assembly import toCAF
from cadquery.occ_impl.geom import Location
from OCP.RWGltf import RWGltf_CafWriter
from OCP.TCollection import TCollection_AsciiString
from OCP.TColStd import TColStd_IndexedDataMapOfStringString
from OCP.Message import Message_ProgressRange

def export_gltf_mm(assy, path, tolerance=1e-3, angular_tolerance=0.1):
    binary = not path.endswith(".gltf")
    orig = assy.loc
    assy.loc *= Location((0, 0, 0), (1, 0, 0), -90)  # Z-up to glTF Y-up, same as cadquery does
    _, doc = toCAF(assy, True, True, tolerance, angular_tolerance)
    writer = RWGltf_CafWriter(TCollection_AsciiString(path), binary)
    writer.ChangeCoordinateSystemConverter().SetInputLengthUnit(0.001)  # model is in mm
    ok = writer.Perform(doc, TColStd_IndexedDataMapOfStringString(), Message_ProgressRange())
    assy.loc = orig
    return ok

Ran it on cadquery 2.8.0: a 100 mm box comes out as +-0.05, a sub-assembly placed at x=200 gets translation: [0.2, 0, 0], and the node tree is the same as the normal export. toCAF is an internal helper so it could move between versions, and tolerances stay in model units (mm) since tessellation happens before the writer scales.

[ghsoares]

Tested on my model, cadquery 2.8.0, meassurements and locations were converted correctly when imported on blender.
Thanks!