Asset_Converter - USD Stage Units Incorrect After GLB to USD Conversion (Should Be in Meters, but Defaults to Centimeters)

Omniverse Isaac Sim
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1

Hi, I’m working on a simulation project in NVIDIA Omniverse and have encountered an issue with unit preservation during GLB to USD conversion.

I create 3D wall assets using Blender and export them in .glb format. In Blender, I make sure that the unit scale is set to meters (Unit Scale = 1.0, Length = Meters). The GLB files saved this way have correct real-world dimensions—for example, a wall 30 meters long is indeed 30 meters in the exported GLB file.

I then convert the GLB to USD using a headless Python script in Isaac Sim with the omni.kit.asset_converter API. Here’s the relevant part of the code I’m using:

python

CopyEdit

# ==== Function: Convert a GLB to USD ====
async def convert_glb_to_usd(input_path: Path, output_path: Path):
    converter = asset_converter.get_instance()
    ctx = asset_converter.AssetConverterContext()

    # Set all meter-related context attributes
    ctx.use_meter_as_world_unit = True  # Set stage metadata to meters

    ctx.ignore_materials = False
    ctx.embed_textures = True
    ctx.allow_material_conversion = True
    ctx.create_materials = True
    ctx.flatten = False 

    task = converter.create_converter_task(str(input_path), str(output_path), ctx)
    await task.wait_until_finished()

    status = task.get_status()
    if status != "succeeded":
        print(f" [SUCCESS] Initial USD Saved: {output_path}")
        return
    print(f"[FAILED]:", task.get_error_message())

Despite setting ctx.use_meter_as_world_unit = True, the resulting USD file still has its stage units in centimeters (metersPerUnit = 0.01).

This leads to a problem:
If I load this USD again and explicitly set the stage metadata using:

python

stage.SetMetadata("metersPerUnit", 1.0)

Then the 30-meter wall which was stored as 3000 cm in the USD (using the above asset_converter) is now interpreted as 3000 meters, which is incorrect. This forces me to manually scale the model down to 0.01 to fix it, which I want to avoid entirely.

My Goal:

I’m looking for a reliable way to convert a GLB (authored in meters) to USD such that:

  • The world units are set to meters (metersPerUnit = 1.0)
  • The geometry is correctly scaled (i.e., a 30 m wall stays 30 m in USD, not 3000 m)

I found this JSON example in some documentation that seems to imply such a configuration is possible:

json

{
  "import_path": "/path/to/animated_model.glb",
  "output_path": "/path/to/output/animated_model.usd",
  "converter_settings": {
    "merge_all_meshes": false,
    "smooth_normals": true,
    "embed_mdl_in_usd": true,
    "embed_textures": true,
    "create_world_as_default_root_prim": true,
    "ignore_animations": false,
    "ignore_camera": false,
    "ignore_light": false,
    "ignore_materials": false,
    "use_meter_as_world_unit": true
  }
}

But I’m not sure how to apply this correctly using the Python API, and whether it handles the scaling properly internally.

Is there a known way to preserve actual meter dimensions during GLB → USD conversion and set the USD’s metersPerUnit = 1.0 without creating the 100× scaling issue?

Thanks in advance for any help!

2

Please try your conversion process with Isaac Sim 5.0 and see if the omni.kit.asset_converter API or its internal handling of unit conversions has been improved, potentially addressing the metersPerUnit issue you’re encountering.

3

ok, I will try it in Isaac Sim 5.0, and let you know

1 Like
4

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