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cj_to_gltf

Scripts to load CityJSON files exported by the other scripts and export to a dual CityJSON/glTF format by transferring all the geometry to glTF.

Classes:

Name Description
Cityjson2Gltf

Load a CityJSON file and transforms it into a pair formed by a glTF file storing the geometry and a CityJSON file storing the attributes.

Cityjson2Gltf

Bases: data_pipeline.cj_loading.cj_loader.CityjsonLoader

Load a CityJSON file and transforms it into a pair formed by a glTF file storing the geometry and a CityJSON file storing the attributes. The hierarchy of the CityJSON file is fully preserved, only the geometry is removed and stored in glTF, with identifiers of the form <cityjson_key>-lod_<lod>. The hierarchy of the CityJSON file is also reproduced in glTF, with all LoDs stored as children of their main object, which has no geometry.

Methods:

Name Description
export

Export the dual representation into the given folder.
make_gltf_scene

Create the scene for glTF, preserving the structure from the CityJSON input.
Source code in python/src/data_pipeline/cj_loading/cj_to_gltf.py 
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class Cityjson2Gltf(CityjsonLoader):
    """
    Load a CityJSON file and transforms it into a pair formed by a glTF file storing the geometry and a CityJSON file storing the attributes.
    The hierarchy of the CityJSON file is fully preserved, only the geometry is removed and stored in glTF, with identifiers of the form `<cityjson_key>-lod_<lod>`.
    The hierarchy of the CityJSON file is also reproduced in glTF, with all LoDs stored as children of their main object, which has no geometry.
    """

    def __init__(self, cj_path: Path) -> None:
        super().__init__(cj_path)

    def make_gltf_scene(self):
        """
        Create the scene for glTF, preserving the structure from the CityJSON input.
        """
        objects: dict[str, dict] = self.data["CityObjects"]
        scene = trimesh.Scene()

        # First insert all the objects without hierarchy
        for obj_key, obj in tqdm(objects.items(), desc="Inserting the objects"):
            meshes_lods = cj_object_to_mesh(
                obj_dict=obj,
                vertices=self.vertices,
            )
            # Insert an empty node so children can still to it
            scene.graph.update(frame_to=obj_key, frame_from=None, matrix=np.eye(4))
            if meshes_lods is not None:
                for lod, mesh in meshes_lods.items():
                    scene.add_geometry(
                        mesh,
                        node_name=obj_key + "-lod_" + lod,
                        parent_node_name=obj_key,
                    )

        # Then set up the structure
        for obj_key, obj in tqdm(objects.items(), desc="Setting up the structure"):
            parent = obj.get("parent", None)
            if parent is not None:
                # Attach child node to its parent in the scene graph
                scene.graph.update(
                    frame_to=obj_key,
                    frame_from=parent,
                    matrix=np.eye(4),
                )
            # If the object defines explicit "children", ensure they are linked too
            for child_id in obj.get("children", []):
                scene.graph.update(
                    frame_to=child_id,
                    frame_from=obj_key,
                    matrix=np.eye(4),
                )

        self.scene = scene

    def export(self, output_folder: Path, overwrite: bool = False) -> None:
        """
        Export the dual representation into the given folder.

        Parameters
        ----------
        output_folder : Path
            The path to the folder where the files should be written.
        overwrite : bool, optional
            Whether to overwrite the files if they exist.
            By default False.

        Raises
        ------
        RuntimeError
            If the path of any of the two outputs already exists and `overwrite` was not set to True.
        """
        output_folder.mkdir(parents=True, exist_ok=overwrite)
        glb_path = output_folder / "geometry.glb"
        cj_path = output_folder / "attributes.city.json"
        if not overwrite:
            if glb_path.exists():
                raise RuntimeError(
                    f"File {glb_path} already exists. Set `overwrite` to True to overwrite."
                )
            if cj_path.exists():
                raise RuntimeError(
                    f"File {cj_path} already exists. Set `overwrite` to True to overwrite."
                )

        # Write the glb file with geometry
        self.scene.export(glb_path)

        # Write the CityJSON file with structure and attributes
        cj_data_copy = deepcopy(self.data)
        objects: dict[str, dict[str, Any]] = cj_data_copy["CityObjects"]
        # Remove the geometry
        for obj in objects.values():
            if "geometry" in obj:
                obj.pop("geometry")
        cj_data_copy["vertices"] = []
        with open(cj_path, "w") as cj_file:
            json.dump(cj_data_copy, cj_file)

export(output_folder, overwrite=False)

Export the dual representation into the given folder.

Parameters:

Name Type Description Default
output_folder pathlib.Path

The path to the folder where the files should be written.

 required
overwrite bool

Whether to overwrite the files if they exist. By default False.

 False

Raises:

Type Description
RuntimeError

If the path of any of the two outputs already exists and overwrite was not set to True.
Source code in python/src/data_pipeline/cj_loading/cj_to_gltf.py 
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def export(self, output_folder: Path, overwrite: bool = False) -> None:
    """
    Export the dual representation into the given folder.

    Parameters
    ----------
    output_folder : Path
        The path to the folder where the files should be written.
    overwrite : bool, optional
        Whether to overwrite the files if they exist.
        By default False.

    Raises
    ------
    RuntimeError
        If the path of any of the two outputs already exists and `overwrite` was not set to True.
    """
    output_folder.mkdir(parents=True, exist_ok=overwrite)
    glb_path = output_folder / "geometry.glb"
    cj_path = output_folder / "attributes.city.json"
    if not overwrite:
        if glb_path.exists():
            raise RuntimeError(
                f"File {glb_path} already exists. Set `overwrite` to True to overwrite."
            )
        if cj_path.exists():
            raise RuntimeError(
                f"File {cj_path} already exists. Set `overwrite` to True to overwrite."
            )

    # Write the glb file with geometry
    self.scene.export(glb_path)

    # Write the CityJSON file with structure and attributes
    cj_data_copy = deepcopy(self.data)
    objects: dict[str, dict[str, Any]] = cj_data_copy["CityObjects"]
    # Remove the geometry
    for obj in objects.values():
        if "geometry" in obj:
            obj.pop("geometry")
    cj_data_copy["vertices"] = []
    with open(cj_path, "w") as cj_file:
        json.dump(cj_data_copy, cj_file)

make_gltf_scene()

Create the scene for glTF, preserving the structure from the CityJSON input.

Source code in python/src/data_pipeline/cj_loading/cj_to_gltf.py 
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def make_gltf_scene(self):
    """
    Create the scene for glTF, preserving the structure from the CityJSON input.
    """
    objects: dict[str, dict] = self.data["CityObjects"]
    scene = trimesh.Scene()

    # First insert all the objects without hierarchy
    for obj_key, obj in tqdm(objects.items(), desc="Inserting the objects"):
        meshes_lods = cj_object_to_mesh(
            obj_dict=obj,
            vertices=self.vertices,
        )
        # Insert an empty node so children can still to it
        scene.graph.update(frame_to=obj_key, frame_from=None, matrix=np.eye(4))
        if meshes_lods is not None:
            for lod, mesh in meshes_lods.items():
                scene.add_geometry(
                    mesh,
                    node_name=obj_key + "-lod_" + lod,
                    parent_node_name=obj_key,
                )

    # Then set up the structure
    for obj_key, obj in tqdm(objects.items(), desc="Setting up the structure"):
        parent = obj.get("parent", None)
        if parent is not None:
            # Attach child node to its parent in the scene graph
            scene.graph.update(
                frame_to=obj_key,
                frame_from=parent,
                matrix=np.eye(4),
            )
        # If the object defines explicit "children", ensure they are linked too
        for child_id in obj.get("children", []):
            scene.graph.update(
                frame_to=child_id,
                frame_from=obj_key,
                matrix=np.eye(4),
            )

    self.scene = scene