Process Module

process_with_tiles(ept_file, tile_size, output_path, metric, voxel_size, voxel_height=1, buffer_size=0.1, srs=None, hag=False, hag_dtm=False, dtm=None, bounds=None, interpolation=None, remove_outliers=False, cover_min_height=2.0, cover_k=0.5, skip_existing=False, verbose=False, thin_radius=None)

Process a large EPT point cloud by tiling, compute CHM or other metrics for each tile, and write the results to the specified output directory.

Parameters:

Name	Type	Description	Default
ept_file	str	Path to the EPT file containing the point cloud data.	required
tile_size	tuple	Size of each tile as (tile_width, tile_height).	required
output_path	str	Directory where the output files will be saved.	required
metric	str	Metric to compute for each tile ("chm", "fhd", "pai", or "cover").	required
voxel_size	tuple	Voxel resolution as (x_resolution, y_resolution, z_resolution).	required
voxel_height	float	Height of each voxel in meters. Required if metric is "pai".	1
buffer_size	float	Fractional buffer size relative to tile size (e.g., 0.1 for 10% buffer). Defaults to 0.1.	0.1
srs	str	Spatial Reference System for the output. If None, uses SRS from the EPT file.	None
hag	bool	If True, compute Height Above Ground using Delaunay triangulation. Defaults to False.	False
hag_dtm	bool	If True, compute Height Above Ground using a provided DTM raster. Defaults to False.	False
dtm	str	Path to the DTM raster file. Required if hag_dtm is True.	None
bounds	tuple	Spatial bounds to crop the data. Must be of the form ([xmin, xmax], [ymin, ymax], [zmin, zmax]) or ([xmin, xmax], [ymin, ymax]). If None, tiling is done over the entire dataset.	None
interpolation	str or None	Interpolation method for CHM calculation ("linear", "cubic", "nearest", or None).	None
remove_outliers	bool	Whether to remove statistical outliers before calculating metrics. Defaults to False.	False
cover_min_height	float	Height threshold (in meters) for canopy cover (used when metric == "cover"). Defaults to 2.0.	2.0
cover_k	float	Beer–Lambert extinction coefficient for canopy cover. Defaults to 0.5.	0.5
skip_existing	bool	If True, skip tiles whose output file already exists. Defaults to False.	False
verbose	bool	If True, print warnings for empty/invalid tiles and buffer adjustments. Defaults to False.	False
thin_radius	float or None	If provided (> 0), apply Poisson radius-based thinning per tile before metrics. Units are in the same CRS as the data (e.g., meters). Defaults to None.	None

Returns:

Type	Description
None	None

Raises:

Type	Description
ValueError	If an unsupported metric is requested, if buffer or voxel sizes are invalid, or required arguments are missing.
FileNotFoundError	If the EPT or DTM file does not exist, or a required file for processing is missing.

Source code in pyforestscan/process.py

def process_with_tiles(ept_file, tile_size, output_path, metric, voxel_size,
                       voxel_height=1, buffer_size=0.1, srs=None, hag=False,
                       hag_dtm=False, dtm=None, bounds=None, interpolation=None, remove_outliers=False,
                       cover_min_height: float = 2.0, cover_k: float = 0.5,
                       skip_existing: bool = False, verbose: bool = False,
                       thin_radius: float | None = None) -> None:
    """
    Process a large EPT point cloud by tiling, compute CHM or other metrics for each tile,
    and write the results to the specified output directory.

    Args:
        ept_file (str): Path to the EPT file containing the point cloud data.
        tile_size (tuple): Size of each tile as (tile_width, tile_height).
        output_path (str): Directory where the output files will be saved.
        metric (str): Metric to compute for each tile ("chm", "fhd", "pai", or "cover").
        voxel_size (tuple): Voxel resolution as (x_resolution, y_resolution, z_resolution).
        voxel_height (float, optional): Height of each voxel in meters. Required if metric is "pai".
        buffer_size (float, optional): Fractional buffer size relative to tile size (e.g., 0.1 for 10% buffer). Defaults to 0.1.
        srs (str, optional): Spatial Reference System for the output. If None, uses SRS from the EPT file.
        hag (bool, optional): If True, compute Height Above Ground using Delaunay triangulation. Defaults to False.
        hag_dtm (bool, optional): If True, compute Height Above Ground using a provided DTM raster. Defaults to False.
        dtm (str, optional): Path to the DTM raster file. Required if hag_dtm is True.
        bounds (tuple, optional): Spatial bounds to crop the data. Must be of the form
            ([xmin, xmax], [ymin, ymax], [zmin, zmax]) or ([xmin, xmax], [ymin, ymax]).
            If None, tiling is done over the entire dataset.
        interpolation (str or None, optional): Interpolation method for CHM calculation ("linear", "cubic", "nearest", or None).
        remove_outliers (bool, optional): Whether to remove statistical outliers before calculating metrics. Defaults to False.
        cover_min_height (float, optional): Height threshold (in meters) for canopy cover (used when metric == "cover"). Defaults to 2.0.
        cover_k (float, optional): Beer–Lambert extinction coefficient for canopy cover. Defaults to 0.5.
        skip_existing (bool, optional): If True, skip tiles whose output file already exists. Defaults to False.
        verbose (bool, optional): If True, print warnings for empty/invalid tiles and buffer adjustments. Defaults to False.
        thin_radius (float or None, optional): If provided (> 0), apply Poisson radius-based thinning per tile before metrics.
            Units are in the same CRS as the data (e.g., meters). Defaults to None.

    Returns:
        None

    Raises:
        ValueError: If an unsupported metric is requested, if buffer or voxel sizes are invalid, or required arguments are missing.
        FileNotFoundError: If the EPT or DTM file does not exist, or a required file for processing is missing.
    """
    if metric not in ["chm", "fhd", "pai", "cover"]:
        raise ValueError(f"Unsupported metric: {metric}")

    (min_z, max_z) = (None, None)
    if bounds:
        if len(bounds) == 2:
            (min_x, max_x), (min_y, max_y) = bounds
        else:
            (min_x, max_x), (min_y, max_y), (min_z, max_z) = bounds
    else:
        min_x, max_x, min_y, max_y, min_z, max_z = get_bounds_from_ept(ept_file)

    if not srs:
        srs = get_srs_from_ept(ept_file)

    num_tiles_x = int(np.ceil((max_x - min_x) / tile_size[0]))
    num_tiles_y = int(np.ceil((max_y - min_y) / tile_size[1]))
    total_tiles = num_tiles_x * num_tiles_y

    if not os.path.exists(output_path):
        os.makedirs(output_path)

    with tqdm(total=total_tiles, desc="Processing tiles") as pbar:
        for i in range(num_tiles_x):
            for j in range(num_tiles_y):
                # Apply buffer+crop for CHM and for PAI/COVER to avoid seam artifacts.
                if metric in ["chm", "pai", "cover"]:
                    current_buffer_size = buffer_size
                else:
                    current_buffer_size = 0.0

                buffer_x = current_buffer_size * tile_size[0]
                buffer_y = current_buffer_size * tile_size[1]
                tile_min_x = min_x + i * tile_size[0] - buffer_x
                tile_max_x = min_x + (i + 1) * tile_size[0] + buffer_x
                tile_min_y = min_y + j * tile_size[1] - buffer_y
                tile_max_y = min_y + (j + 1) * tile_size[1] + buffer_y

                tile_min_x = max(min_x, tile_min_x)
                tile_max_x = min(max_x, tile_max_x)
                tile_min_y = max(min_y, tile_min_y)
                tile_max_y = min(max_y, tile_max_y)

                if tile_max_x <= tile_min_x or tile_max_y <= tile_min_y:
                    if verbose:
                        print(f"Warning: Skipping tile ({i}, {j}) due to invalid spatial extent.")
                    pbar.update(1)
                    continue

                if metric == "chm":
                    result_file = os.path.join(output_path, f"tile_{i}_{j}_chm.tif")
                else:
                    result_file = os.path.join(output_path, f"tile_{i}_{j}_{metric}.tif")

                if skip_existing and os.path.isfile(result_file):
                    pbar.update(1)
                    continue

                if min_z and max_z:
                    tile_bounds = ([tile_min_x, tile_max_x], [tile_min_y, tile_max_y], [min_z, max_z])
                else:
                    tile_bounds = ([tile_min_x, tile_max_x], [tile_min_y, tile_max_y])
                tile_pipeline_stages = []

                if hag:
                    tile_pipeline_stages.append(_hag_delaunay())
                elif hag_dtm:
                    if not dtm or not os.path.isfile(dtm):
                        raise FileNotFoundError(f"DTM file is required for HAG calculation using DTM: {dtm}")
                    cropped_dtm_path = _crop_dtm(
                        dtm,
                        tile_min_x, tile_min_y,
                        tile_max_x, tile_max_y
                    )
                    tile_pipeline_stages.append(_hag_raster(cropped_dtm_path))
                base_pipeline = {
                    "type": "readers.ept",
                    "filename": ept_file,
                    "bounds": f"{tile_bounds}",
                }
                tile_pipeline_json = {
                    "pipeline": [base_pipeline] + tile_pipeline_stages
                }

                tile_pipeline = pdal.Pipeline(json.dumps(tile_pipeline_json))
                tile_pipeline.execute()

                # Extract points from pipeline output safely
                arrays = tile_pipeline.arrays if hasattr(tile_pipeline, "arrays") else []
                if not arrays or arrays[0].size == 0:
                    if verbose:
                        print(f"Warning: No data in tile ({i}, {j}). Skipping.")
                    pbar.update(1)
                    continue

                if remove_outliers:
                    tile_points = remove_outliers_and_clean(arrays)[0]
                else:
                    tile_points = arrays[0]

                # Optional radius-based thinning before metrics
                if thin_radius is not None and thin_radius > 0:
                    thinned = downsample_poisson([tile_points], thin_radius=thin_radius)
                    tile_points = thinned[0] if thinned else tile_points

                    if tile_points.size == 0:
                        if verbose:
                            print(f"Warning: Tile ({i}, {j}) empty after thinning. Skipping.")
                        pbar.update(1)
                        continue

                buffer_pixels_x = int(np.ceil(buffer_x / voxel_size[0]))
                buffer_pixels_y = int(np.ceil(buffer_y / voxel_size[1]))

                if metric == "chm":
                    chm, extent = calculate_chm(tile_points, voxel_size, interpolation=interpolation)

                    if buffer_pixels_x * 2 >= chm.shape[1] or buffer_pixels_y * 2 >= chm.shape[0]:
                        if verbose:
                            print(
                                f"Warning: Buffer size exceeds CHM dimensions for tile ({i}, {j}). Adjusting buffer size.")
                        buffer_pixels_x = max(0, chm.shape[1] // 2 - 1)
                        buffer_pixels_y = max(0, chm.shape[0] // 2 - 1)

                    # Safe crop: avoid Python's -0 slice behavior producing empty arrays.
                    if buffer_pixels_x < 0 or buffer_pixels_y < 0:
                        raise ValueError("Computed negative buffer pixels; check voxel and buffer sizes.")

                    start_x = buffer_pixels_x
                    end_x = chm.shape[1] - buffer_pixels_x if buffer_pixels_x > 0 else chm.shape[1]
                    start_y = buffer_pixels_y
                    end_y = chm.shape[0] - buffer_pixels_y if buffer_pixels_y > 0 else chm.shape[0]

                    # If cropping would yield an empty array due to small tiles, skip cropping
                    if end_x <= start_x or end_y <= start_y:
                        # Fall back to no buffer crop for this tile
                        core = chm
                    else:
                        core = chm[start_y:end_y, start_x:end_x]

                    chm = core

                    # Derive core extent from CHM grid extent and actual pixel crop to avoid stretching
                    dx, dy = voxel_size[0], voxel_size[1]
                    grid_extent = extent  # [x_min, x_max, y_min, y_max] as returned by calculate_chm
                    core_extent = (
                        grid_extent[0] + buffer_pixels_x * dx,
                        grid_extent[1] - buffer_pixels_x * dx,
                        grid_extent[2] + buffer_pixels_y * dy,
                        grid_extent[3] - buffer_pixels_y * dy,
                    )

                    create_geotiff(chm, result_file, srs, core_extent)
                elif metric in ["fhd", "pai", "cover"]:
                    voxels, spatial_extent = assign_voxels(tile_points, voxel_size)

                    if metric == "fhd":
                        result = calculate_fhd(voxels)
                    elif metric == "pai":
                        if not voxel_height:
                            raise ValueError(f"voxel_height is required for metric {metric}")

                        pad = calculate_pad(voxels, voxel_size[-1])

                        if np.all(pad == 0):
                            result = np.zeros((pad.shape[0], pad.shape[1]))
                        else:
                            # Guard against empty integration range when top height < default min_height
                            effective_max_height = pad.shape[2] * voxel_size[-1]
                            default_min_height = 1.0
                            if default_min_height >= effective_max_height:
                                result = np.zeros((pad.shape[0], pad.shape[1]))
                            else:
                                result = calculate_pai(pad, voxel_height)
                    elif metric == "cover":
                        if not voxel_height:
                            raise ValueError(f"voxel_height is required for metric {metric}")

                        pad = calculate_pad(voxels, voxel_size[-1])
                        if np.all(pad == 0):
                            result = np.zeros((pad.shape[0], pad.shape[1]))
                        else:
                            result = calculate_canopy_cover(
                                pad,
                                voxel_height=voxel_height,
                                min_height=cover_min_height,
                                max_height=None,
                                k=cover_k,
                            )

                    if current_buffer_size > 0:
                        if buffer_pixels_x * 2 >= result.shape[1] or buffer_pixels_y * 2 >= result.shape[0]:
                            if verbose:
                                print(
                                    f"Warning: Buffer size exceeds {metric.upper()} dimensions for tile ({i}, {j}). "
                                    f"Adjusting buffer size."
                                )
                            buffer_pixels_x = max(0, result.shape[1] // 2 - 1)
                            buffer_pixels_y = max(0, result.shape[0] // 2 - 1)

                        # Safe crop (avoid -0 slicing)
                        start_x = buffer_pixels_x
                        end_x = result.shape[1] - buffer_pixels_x if buffer_pixels_x > 0 else result.shape[1]
                        start_y = buffer_pixels_y
                        end_y = result.shape[0] - buffer_pixels_y if buffer_pixels_y > 0 else result.shape[0]

                        if end_x > start_x and end_y > start_y:
                            result = result[start_y:end_y, start_x:end_x]

                    # Derive core extent from voxel grid extent and applied pixel crop to avoid stretching
                    dx, dy = voxel_size[0], voxel_size[1]
                    core_extent = (
                        spatial_extent[0] + buffer_pixels_x * dx,
                        spatial_extent[1] - buffer_pixels_x * dx,
                        spatial_extent[2] + buffer_pixels_y * dy,
                        spatial_extent[3] - buffer_pixels_y * dy,
                    )

                    if core_extent[1] <= core_extent[0] or core_extent[3] <= core_extent[2]:
                        if verbose:
                            print(f"Warning: Invalid core extent for tile ({i}, {j}): {core_extent}. Skipping.")
                        pbar.update(1)
                        continue

                    create_geotiff(result, result_file, srs, core_extent)
                else:
                    raise ValueError(f"Unsupported metric: {metric}")

                pbar.update(1)