Source code for omni.isaac.lab.sim.converters.mesh_converter

# Copyright (c) 2022-2024, The Isaac Lab Project Developers.
# All rights reserved.
#
# SPDX-License-Identifier: BSD-3-Clause

import asyncio
import os

import omni
import omni.kit.commands
import omni.usd
from omni.isaac.core.utils.extensions import enable_extension
from pxr import Gf, Tf, Usd, UsdGeom, UsdPhysics, UsdUtils

from omni.isaac.lab.sim.converters.asset_converter_base import AssetConverterBase
from omni.isaac.lab.sim.converters.mesh_converter_cfg import MeshConverterCfg
from omni.isaac.lab.sim.schemas import schemas
from omni.isaac.lab.sim.utils import export_prim_to_file


[docs]class MeshConverter(AssetConverterBase): """Converter for a mesh file in OBJ / STL / FBX format to a USD file. This class wraps around the `omni.kit.asset_converter`_ extension to provide a lazy implementation for mesh to USD conversion. It stores the output USD file in an instanceable format since that is what is typically used in all learning related applications. To make the asset instanceable, we must follow a certain structure dictated by how USD scene-graph instancing and physics work. The rigid body component must be added to each instance and not the referenced asset (i.e. the prototype prim itself). This is because the rigid body component defines properties that are specific to each instance and cannot be shared under the referenced asset. For more information, please check the `documentation <https://docs.omniverse.nvidia.com/extensions/latest/ext_physics/rigid-bodies.html#instancing-rigid-bodies>`_. Due to the above, we follow the following structure: * ``{prim_path}`` - The root prim that is an Xform with the rigid body and mass APIs if configured. * ``{prim_path}/geometry`` - The prim that contains the mesh and optionally the materials if configured. If instancing is enabled, this prim will be an instanceable reference to the prototype prim. .. _omni.kit.asset_converter: https://docs.omniverse.nvidia.com/extensions/latest/ext_asset-converter.html .. caution:: When converting STL files, Z-up convention is assumed, even though this is not the default for many CAD export programs. Asset orientation convention can either be modified directly in the CAD program's export process or an offset can be added within the config in Isaac Lab. """ cfg: MeshConverterCfg """The configuration instance for mesh to USD conversion."""
[docs] def __init__(self, cfg: MeshConverterCfg): """Initializes the class. Args: cfg: The configuration instance for mesh to USD conversion. """ super().__init__(cfg=cfg)
""" Implementation specific methods. """ def _convert_asset(self, cfg: MeshConverterCfg): """Generate USD from OBJ, STL or FBX. The USD file has Y-up axis and is scaled to meters. The asset hierarchy is arranged as follows: .. code-block:: none mesh_file_basename (default prim) |- /geometry/Looks |- /geometry/mesh Args: cfg: The configuration for conversion of mesh to USD. Raises: RuntimeError: If the conversion using the Omniverse asset converter fails. """ # resolve mesh name and format mesh_file_basename, mesh_file_format = os.path.basename(cfg.asset_path).split(".") mesh_file_format = mesh_file_format.lower() # Check if mesh_file_basename is a valid USD identifier if not Tf.IsValidIdentifier(mesh_file_basename): # Correct the name to a valid identifier and update the basename mesh_file_basename_original = mesh_file_basename mesh_file_basename = Tf.MakeValidIdentifier(mesh_file_basename) omni.log.warn( f"Input file name '{mesh_file_basename_original}' is an invalid identifier for the mesh prim path." f" Renaming it to '{mesh_file_basename}' for the conversion." ) # Convert USD asyncio.get_event_loop().run_until_complete( self._convert_mesh_to_usd(in_file=cfg.asset_path, out_file=self.usd_path) ) # Create a new stage, set Z up and meters per unit temp_stage = Usd.Stage.CreateInMemory() UsdGeom.SetStageUpAxis(temp_stage, UsdGeom.Tokens.z) UsdGeom.SetStageMetersPerUnit(temp_stage, 1.0) UsdPhysics.SetStageKilogramsPerUnit(temp_stage, 1.0) # Add mesh to stage base_prim = temp_stage.DefinePrim(f"/{mesh_file_basename}", "Xform") prim = temp_stage.DefinePrim(f"/{mesh_file_basename}/geometry", "Xform") prim.GetReferences().AddReference(self.usd_path) temp_stage.SetDefaultPrim(base_prim) temp_stage.Export(self.usd_path) # Open converted USD stage stage = Usd.Stage.Open(self.usd_path) # Need to reload the stage to get the new prim structure, otherwise it can be taken from the cache stage.Reload() # Add USD to stage cache stage_id = UsdUtils.StageCache.Get().Insert(stage) # Get the default prim (which is the root prim) -- "/{mesh_file_basename}" xform_prim = stage.GetDefaultPrim() geom_prim = stage.GetPrimAtPath(f"/{mesh_file_basename}/geometry") # Move all meshes to underneath new Xform for child_mesh_prim in geom_prim.GetChildren(): if child_mesh_prim.GetTypeName() == "Mesh": # Apply collider properties to mesh if cfg.collision_props is not None: # -- Collision approximation to mesh # TODO: Move this to a new Schema: https://github.com/isaac-orbit/IsaacLab/issues/163 mesh_collision_api = UsdPhysics.MeshCollisionAPI.Apply(child_mesh_prim) mesh_collision_api.GetApproximationAttr().Set(cfg.collision_approximation) # -- Collider properties such as offset, scale, etc. schemas.define_collision_properties( prim_path=child_mesh_prim.GetPath(), cfg=cfg.collision_props, stage=stage ) # Delete the old Xform and make the new Xform the default prim stage.SetDefaultPrim(xform_prim) # Apply default Xform rotation to mesh -> enable to set rotation and scale omni.kit.commands.execute( "CreateDefaultXformOnPrimCommand", prim_path=xform_prim.GetPath(), **{"stage": stage}, ) # Apply translation, rotation, and scale to the Xform geom_xform = UsdGeom.Xform(geom_prim) geom_xform.ClearXformOpOrder() # Remove any existing rotation attributes rotate_attr = geom_prim.GetAttribute("xformOp:rotateXYZ") if rotate_attr: geom_prim.RemoveProperty(rotate_attr.GetName()) # translation translate_op = geom_xform.AddTranslateOp(UsdGeom.XformOp.PrecisionDouble) translate_op.Set(Gf.Vec3d(*cfg.translation)) # rotation orient_op = geom_xform.AddOrientOp(UsdGeom.XformOp.PrecisionDouble) orient_op.Set(Gf.Quatd(*cfg.rotation)) # scale scale_op = geom_xform.AddScaleOp(UsdGeom.XformOp.PrecisionDouble) scale_op.Set(Gf.Vec3d(*cfg.scale)) # Handle instanceable # Create a new Xform prim that will be the prototype prim if cfg.make_instanceable: # Export Xform to a file so we can reference it from all instances export_prim_to_file( path=os.path.join(self.usd_dir, self.usd_instanceable_meshes_path), source_prim_path=geom_prim.GetPath(), stage=stage, ) # Delete the original prim that will now be a reference geom_prim_path = geom_prim.GetPath().pathString omni.kit.commands.execute("DeletePrims", paths=[geom_prim_path], stage=stage) # Update references to exported Xform and make it instanceable geom_undef_prim = stage.DefinePrim(geom_prim_path) geom_undef_prim.GetReferences().AddReference(self.usd_instanceable_meshes_path, primPath=geom_prim_path) geom_undef_prim.SetInstanceable(True) # Apply mass and rigid body properties after everything else # Properties are applied to the top level prim to avoid the case where all instances of this # asset unintentionally share the same rigid body properties # apply mass properties if cfg.mass_props is not None: schemas.define_mass_properties(prim_path=xform_prim.GetPath(), cfg=cfg.mass_props, stage=stage) # apply rigid body properties if cfg.rigid_props is not None: schemas.define_rigid_body_properties(prim_path=xform_prim.GetPath(), cfg=cfg.rigid_props, stage=stage) # Save changes to USD stage stage.Save() if stage_id is not None: UsdUtils.StageCache.Get().Erase(stage_id) """ Helper methods. """ @staticmethod async def _convert_mesh_to_usd(in_file: str, out_file: str, load_materials: bool = True) -> bool: """Convert mesh from supported file types to USD. This function uses the Omniverse Asset Converter extension to convert a mesh file to USD. It is an asynchronous function and should be called using `asyncio.get_event_loop().run_until_complete()`. The converted asset is stored in the USD format in the specified output file. The USD file has Y-up axis and is scaled to cm. Args: in_file: The file to convert. out_file: The path to store the output file. load_materials: Set to True to enable attaching materials defined in the input file to the generated USD mesh. Defaults to True. Returns: True if the conversion succeeds. """ enable_extension("omni.kit.asset_converter") import omni.kit.asset_converter import omni.usd # Create converter context converter_context = omni.kit.asset_converter.AssetConverterContext() # Set up converter settings # Don't import/export materials converter_context.ignore_materials = not load_materials converter_context.ignore_animations = True converter_context.ignore_camera = True converter_context.ignore_light = True # Merge all meshes into one converter_context.merge_all_meshes = True # Sets world units to meters, this will also scale asset if it's centimeters model. # This does not work right now :(, so we need to scale the mesh manually converter_context.use_meter_as_world_unit = True converter_context.baking_scales = True # Uses double precision for all transform ops. converter_context.use_double_precision_to_usd_transform_op = True # Create converter task instance = omni.kit.asset_converter.get_instance() task = instance.create_converter_task(in_file, out_file, None, converter_context) # Start conversion task and wait for it to finish success = await task.wait_until_finished() if not success: raise RuntimeError(f"Failed to convert {in_file} to USD. Error: {task.get_error_message()}") return success