cj_loader

Scripts to load CityJSON files.

Classes:

Name	Description
CityjsonLoader	Utility CityJSON loader that extracts all data from a CityJSON file and transforms the integer coordinates to their real coordinates.

Functions:

Name	Description
cj_object_to_mesh	Build the Trimesh representation of the geometry, based on a full CityJSON object.

CityjsonLoader

Utility CityJSON loader that extracts all data from a CityJSON file and transforms the integer coordinates to their real coordinates.

Source code in python/src/data_pipeline/cj_loading/cj_loader.py

class CityjsonLoader:
    """
    Utility CityJSON loader that extracts all data from a CityJSON file and transforms the integer coordinates to their real coordinates.
    """

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

        self.data = self._cj_load()
        self.vertices = self._cj_extract_vertices()

    def _cj_load(self) -> dict[str, Any]:
        """
        Load the whole file.

        Returns
        -------
        dict[str, Any]
            The CityJSON file directly as a dictionary.
        """
        with open(self.path) as cj_file:
            cj_data = json.load(cj_file)

        return cj_data

    def _cj_extract_vertices(self) -> NDArray[np.float64]:
        """
        Extract and transforms the vertices to their real coordinates.

        Returns
        -------
        NDArray[np.float64]
            The array (N, 3) of vertices coordinates.
        """
        normalised_vertices = np.array(self.data["vertices"], dtype=np.float64)
        translate = np.array(self.data["transform"]["translate"], dtype=np.float64)
        scale = np.array(self.data["transform"]["scale"], dtype=np.float64)
        vertices = scale * normalised_vertices + translate
        return vertices

cj_object_to_mesh(obj_dict, vertices)

Build the Trimesh representation of the geometry, based on a full CityJSON object. All the LoDs are created and returned.

Parameters:

Name	Type	Description	Default
obj_dict	dict[str, typing.Any]	The full CityJSON object as stored in the file. In particular, the geometry with potentally multiple LoDs is expected to be stored in "geometry".	required
vertices	numpy.typing.NDArray[numpy.float64]	The array (N,3) of the vertices coordinates, that the geometry refers to.	required

Returns:

Type	Description
dict[str, trimesh.Trimesh] | None	A dictionary mapping the LoD to its Trimesh representation.

Raises:

Type	Description
NotImplementedError	If the geometry is not one of the supported geometry types.

Source code in python/src/data_pipeline/cj_loading/cj_loader.py

def cj_object_to_mesh(
    obj_dict: dict[str, Any], vertices: NDArray[np.float64]
) -> dict[str, trimesh.Trimesh] | None:
    """
    Build the Trimesh representation of the geometry, based on a full CityJSON object.
    All the LoDs are created and returned.

    Parameters
    ----------
    obj_dict : dict[str, Any]
        The full CityJSON object as stored in the file.
        In particular, the geometry with potentally multiple LoDs is expected to be stored in "geometry".
    vertices : NDArray[np.float64]
        The array (N,3) of the vertices coordinates, that the geometry refers to.

    Returns
    -------
    dict[str, trimesh.Trimesh] | None
        A dictionary mapping the LoD to its Trimesh representation.

    Raises
    ------
    NotImplementedError
        If the geometry is not one of the supported geometry types.
    """

    # Return None if there is no geometry
    if "geometry" not in obj_dict or len(obj_dict["geometry"]) == 0:
        return None

    # CityObjects may contain several geometry entries (different LoDs)
    meshes_lods = {}
    for geom in obj_dict["geometry"]:
        lod = geom["lod"]
        geom_type = geom["type"]
        boundaries = geom["boundaries"]
        if geom_type == "MultiSurface":
            mesh = _cj_multisurface_to_mesh(
                boundaries=boundaries,
                vertices=vertices,
            )
        elif geom_type == "Solid":
            mesh = _cj_solid_to_mesh(
                boundaries=boundaries,
                vertices=vertices,
            )
        else:
            raise NotImplementedError(f"Unexpected geometry type: '{geom_type}'")
        meshes_lods[lod] = mesh

    return meshes_lods