"""Stream order extraction: Strahler and Shreve ordering of drainage networks.
Assigns hierarchical order values to stream cells derived from a D8
flow direction grid and a flow accumulation grid. Cells with
accumulation below a user-defined threshold are non-stream and receive
NaN. Two methods are supported:
* **Strahler**: headwaters = 1; when two streams of equal order meet
the downstream order increments by 1; otherwise the higher order
propagates.
* **Shreve**: headwaters = 1; at each confluence the downstream
magnitude equals the sum of all incoming magnitudes.
Algorithm
---------
CPU : Kahn's BFS topological sort among stream cells — O(N_stream).
GPU : iterative frontier peeling with pull-based kernels.
Dask: iterative tile sweep with boundary propagation, same pattern
as ``flow_accumulation.py``.
"""
from __future__ import annotations
import numpy as np
import xarray as xr
from numba import cuda
try:
import cupy
except ImportError:
class cupy: # type: ignore[no-redef]
ndarray = False
try:
import dask.array as da
except ImportError:
da = None
from xrspatial.dataset_support import supports_dataset
from xrspatial.hydro._boundary_store import BoundaryStore
from xrspatial.hydro.flow_accumulation_d8 import _code_to_offset, _code_to_offset_py
from xrspatial.utils import (_validate_raster, cuda_args, has_cuda_and_cupy, is_cupy_array,
is_dask_cupy, ngjit)
# =====================================================================
# Memory guards
# =====================================================================
#
# CPU peak working set per pixel for the eager Strahler/Shreve kernels:
# order : float64 -> 8
# in_degree : int32 -> 4
# max_in : float64 -> 8 (Strahler only; Shreve omits it)
# cnt_max : int32 -> 4 (Strahler only)
# queue_r : int64 -> 8
# queue_c : int64 -> 8
# Total ~40 bytes/pixel for Strahler, ~32 for Shreve. We budget for the
# worst case. Caller-provided ``flow_dir`` and ``flow_accum`` already
# live in RAM before the kernel runs and are not double-counted here.
_BYTES_PER_PIXEL = 40
# GPU peak working set per pixel for ``_stream_order_cupy``:
# flow_dir_f64 : float64 -> 8
# stream_mask_i8 : int8 -> 1
# in_degree : int32 -> 4
# state : int32 -> 4
# order : float64 -> 8
# max_in : float64 -> 8
# cnt_max : int32 -> 4
# Total ~37 bytes/pixel. The ``fa`` input copy adds 8 B/px on the
# device but is created from the caller's CuPy array. Use 40 B/px as
# a conservative budget.
_GPU_BYTES_PER_PIXEL = 40
def _available_memory_bytes():
"""Best-effort estimate of available host memory in bytes."""
try:
with open('/proc/meminfo', 'r') as f:
for line in f:
if line.startswith('MemAvailable:'):
return int(line.split()[1]) * 1024 # kB -> bytes
except (OSError, ValueError, IndexError):
pass
try:
import psutil
return psutil.virtual_memory().available
except (ImportError, AttributeError):
pass
return 2 * 1024 ** 3
def _available_gpu_memory_bytes():
"""Best-effort estimate of free GPU memory in bytes.
Returns 0 if CuPy / CUDA is unavailable or the query fails -- callers
use that as a sentinel meaning "no GPU info, skip the guard".
"""
try:
import cupy as _cp
free, _total = _cp.cuda.runtime.memGetInfo()
return int(free)
except Exception:
return 0
def _check_memory(height, width):
"""Raise MemoryError if the kernel would exceed 50% of RAM."""
required = int(height) * int(width) * _BYTES_PER_PIXEL
available = _available_memory_bytes()
if required > 0.5 * available:
raise MemoryError(
f"stream_order_d8 on a {height}x{width} grid requires "
f"~{required / 1e9:.1f} GB of working memory but only "
f"~{available / 1e9:.1f} GB is available. Use a "
f"dask-backed DataArray for out-of-core processing."
)
def _check_gpu_memory(height, width):
"""Raise MemoryError if the CuPy kernel would exceed 50% of free GPU RAM.
Skips the check (returns silently) when ``_available_gpu_memory_bytes``
cannot determine the free memory -- e.g. on hosts without CUDA, where
the kernel will fail at the cupy.asarray boundary anyway.
"""
available = _available_gpu_memory_bytes()
if available <= 0:
return
required = int(height) * int(width) * _GPU_BYTES_PER_PIXEL
if required > 0.5 * available:
raise MemoryError(
f"stream_order_d8 on a {height}x{width} grid requires "
f"~{required / 1e9:.1f} GB of GPU working memory but only "
f"~{available / 1e9:.1f} GB is free on the active device. "
f"Use a dask+cupy DataArray for out-of-core processing."
)
def _to_numpy_f64(arr):
"""Convert *arr* to a contiguous numpy float64 array (handles CuPy)."""
if hasattr(arr, 'get'):
arr = arr.get()
return np.asarray(arr, dtype=np.float64)
# =====================================================================
# CPU kernels
# =====================================================================
@ngjit
def _strahler_cpu(flow_dir, stream_mask, height, width):
"""Kahn's BFS Strahler ordering among stream cells."""
order = np.empty((height, width), dtype=np.float64)
in_degree = np.zeros((height, width), dtype=np.int32)
max_in = np.zeros((height, width), dtype=np.float64)
cnt_max = np.zeros((height, width), dtype=np.int32)
# Initialise
for r in range(height):
for c in range(width):
if stream_mask[r, c] == 0:
order[r, c] = np.nan
else:
order[r, c] = 0.0
# Compute in-degrees (only among stream cells)
for r in range(height):
for c in range(width):
if stream_mask[r, c] == 0:
continue
v = flow_dir[r, c]
if v != v: # NaN
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if 0 <= nr < height and 0 <= nc < width and stream_mask[nr, nc] == 1:
in_degree[nr, nc] += 1
# BFS queue
queue_r = np.empty(height * width, dtype=np.int64)
queue_c = np.empty(height * width, dtype=np.int64)
head = np.int64(0)
tail = np.int64(0)
# Enqueue headwaters (stream cells with in_degree == 0)
for r in range(height):
for c in range(width):
if stream_mask[r, c] == 1 and in_degree[r, c] == 0:
order[r, c] = 1.0
queue_r[tail] = r
queue_c[tail] = c
tail += 1
while head < tail:
r = queue_r[head]
c = queue_c[head]
head += 1
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if not (0 <= nr < height and 0 <= nc < width and stream_mask[nr, nc] == 1):
continue
cur_ord = order[r, c]
if cur_ord > max_in[nr, nc]:
max_in[nr, nc] = cur_ord
cnt_max[nr, nc] = 1
elif cur_ord == max_in[nr, nc]:
cnt_max[nr, nc] += 1
in_degree[nr, nc] -= 1
if in_degree[nr, nc] == 0:
if cnt_max[nr, nc] >= 2:
order[nr, nc] = max_in[nr, nc] + 1.0
else:
order[nr, nc] = max_in[nr, nc]
queue_r[tail] = nr
queue_c[tail] = nc
tail += 1
return order
@ngjit
def _shreve_cpu(flow_dir, stream_mask, height, width):
"""Kahn's BFS Shreve ordering among stream cells."""
order = np.empty((height, width), dtype=np.float64)
in_degree = np.zeros((height, width), dtype=np.int32)
for r in range(height):
for c in range(width):
if stream_mask[r, c] == 0:
order[r, c] = np.nan
else:
order[r, c] = 0.0
for r in range(height):
for c in range(width):
if stream_mask[r, c] == 0:
continue
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if 0 <= nr < height and 0 <= nc < width and stream_mask[nr, nc] == 1:
in_degree[nr, nc] += 1
queue_r = np.empty(height * width, dtype=np.int64)
queue_c = np.empty(height * width, dtype=np.int64)
head = np.int64(0)
tail = np.int64(0)
for r in range(height):
for c in range(width):
if stream_mask[r, c] == 1 and in_degree[r, c] == 0:
order[r, c] = 1.0
queue_r[tail] = r
queue_c[tail] = c
tail += 1
while head < tail:
r = queue_r[head]
c = queue_c[head]
head += 1
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if not (0 <= nr < height and 0 <= nc < width and stream_mask[nr, nc] == 1):
continue
order[nr, nc] += order[r, c]
in_degree[nr, nc] -= 1
if in_degree[nr, nc] == 0:
queue_r[tail] = nr
queue_c[tail] = nc
tail += 1
return order
# =====================================================================
# GPU kernels
# =====================================================================
@cuda.jit
def _stream_order_init_gpu(flow_dir, stream_mask, in_degree, state,
order, max_in, cnt_max, H, W):
"""Initialise GPU arrays for stream order computation."""
i, j = cuda.grid(2)
if i >= H or j >= W:
return
if stream_mask[i, j] == 0:
state[i, j] = 0
order[i, j] = 0.0
max_in[i, j] = 0.0
cnt_max[i, j] = 0
return
state[i, j] = 1
order[i, j] = 0.0
max_in[i, j] = 0.0
cnt_max[i, j] = 0
v = flow_dir[i, j]
if v != v:
return
code = int(v)
dy = 0
dx = 0
if code == 1:
dy, dx = 0, 1
elif code == 2:
dy, dx = 1, 1
elif code == 4:
dy, dx = 1, 0
elif code == 8:
dy, dx = 1, -1
elif code == 16:
dy, dx = 0, -1
elif code == 32:
dy, dx = -1, -1
elif code == 64:
dy, dx = -1, 0
elif code == 128:
dy, dx = -1, 1
if dy == 0 and dx == 0:
return
ni = i + dy
nj = j + dx
if 0 <= ni < H and 0 <= nj < W and stream_mask[ni, nj] == 1:
cuda.atomic.add(in_degree, (ni, nj), 1)
@cuda.jit
def _stream_order_find_ready(in_degree, state, order, changed, H, W):
"""Finalize previous frontier, mark new frontier cells."""
i, j = cuda.grid(2)
if i >= H or j >= W:
return
if state[i, j] == 2:
state[i, j] = 3
if state[i, j] == 1 and in_degree[i, j] == 0:
state[i, j] = 2
if order[i, j] == 0.0:
order[i, j] = 1.0 # headwater
cuda.atomic.add(changed, 0, 1)
@cuda.jit
def _stream_order_pull_strahler(flow_dir, stream_mask, in_degree, state,
order, max_in, cnt_max, H, W):
"""Active cells pull Strahler info from frontier neighbours."""
i, j = cuda.grid(2)
if i >= H or j >= W:
return
if state[i, j] != 1:
return
for k in range(8):
if k == 0:
dy, dx = 0, 1
elif k == 1:
dy, dx = 1, 1
elif k == 2:
dy, dx = 1, 0
elif k == 3:
dy, dx = 1, -1
elif k == 4:
dy, dx = 0, -1
elif k == 5:
dy, dx = -1, -1
elif k == 6:
dy, dx = -1, 0
else:
dy, dx = -1, 1
ni = i + dy
nj = j + dx
if ni < 0 or ni >= H or nj < 0 or nj >= W:
continue
if state[ni, nj] != 2:
continue
if stream_mask[ni, nj] == 0:
continue
nv = flow_dir[ni, nj]
ncode = int(nv)
ndy = 0
ndx = 0
if ncode == 1:
ndy, ndx = 0, 1
elif ncode == 2:
ndy, ndx = 1, 1
elif ncode == 4:
ndy, ndx = 1, 0
elif ncode == 8:
ndy, ndx = 1, -1
elif ncode == 16:
ndy, ndx = 0, -1
elif ncode == 32:
ndy, ndx = -1, -1
elif ncode == 64:
ndy, ndx = -1, 0
elif ncode == 128:
ndy, ndx = -1, 1
if ni + ndy == i and nj + ndx == j:
nb_ord = order[ni, nj]
if nb_ord > max_in[i, j]:
max_in[i, j] = nb_ord
cnt_max[i, j] = 1
elif nb_ord == max_in[i, j]:
cnt_max[i, j] += 1
in_degree[i, j] -= 1
if in_degree[i, j] == 0:
if cnt_max[i, j] >= 2:
order[i, j] = max_in[i, j] + 1.0
else:
order[i, j] = max_in[i, j]
@cuda.jit
def _stream_order_pull_shreve(flow_dir, stream_mask, in_degree, state,
order, H, W):
"""Active cells pull Shreve magnitudes from frontier neighbours."""
i, j = cuda.grid(2)
if i >= H or j >= W:
return
if state[i, j] != 1:
return
for k in range(8):
if k == 0:
dy, dx = 0, 1
elif k == 1:
dy, dx = 1, 1
elif k == 2:
dy, dx = 1, 0
elif k == 3:
dy, dx = 1, -1
elif k == 4:
dy, dx = 0, -1
elif k == 5:
dy, dx = -1, -1
elif k == 6:
dy, dx = -1, 0
else:
dy, dx = -1, 1
ni = i + dy
nj = j + dx
if ni < 0 or ni >= H or nj < 0 or nj >= W:
continue
if state[ni, nj] != 2:
continue
if stream_mask[ni, nj] == 0:
continue
nv = flow_dir[ni, nj]
ncode = int(nv)
ndy = 0
ndx = 0
if ncode == 1:
ndy, ndx = 0, 1
elif ncode == 2:
ndy, ndx = 1, 1
elif ncode == 4:
ndy, ndx = 1, 0
elif ncode == 8:
ndy, ndx = 1, -1
elif ncode == 16:
ndy, ndx = 0, -1
elif ncode == 32:
ndy, ndx = -1, -1
elif ncode == 64:
ndy, ndx = -1, 0
elif ncode == 128:
ndy, ndx = -1, 1
if ni + ndy == i and nj + ndx == j:
order[i, j] += order[ni, nj]
in_degree[i, j] -= 1
def _stream_order_cupy(flow_dir_data, stream_mask_data, method):
"""GPU driver for stream order computation."""
import cupy as cp
H, W = flow_dir_data.shape
flow_dir_f64 = flow_dir_data.astype(cp.float64)
stream_mask_i8 = stream_mask_data.astype(cp.int8)
in_degree = cp.zeros((H, W), dtype=cp.int32)
state = cp.zeros((H, W), dtype=cp.int32)
order = cp.zeros((H, W), dtype=cp.float64)
max_in = cp.zeros((H, W), dtype=cp.float64)
cnt_max = cp.zeros((H, W), dtype=cp.int32)
changed = cp.zeros(1, dtype=cp.int32)
griddim, blockdim = cuda_args((H, W))
_stream_order_init_gpu[griddim, blockdim](
flow_dir_f64, stream_mask_i8, in_degree, state,
order, max_in, cnt_max, H, W)
max_iter = H * W
for _ in range(max_iter):
changed[0] = 0
_stream_order_find_ready[griddim, blockdim](
in_degree, state, order, changed, H, W)
if int(changed[0]) == 0:
break
if method == 'strahler':
_stream_order_pull_strahler[griddim, blockdim](
flow_dir_f64, stream_mask_i8, in_degree, state,
order, max_in, cnt_max, H, W)
else:
_stream_order_pull_shreve[griddim, blockdim](
flow_dir_f64, stream_mask_i8, in_degree, state,
order, H, W)
order = cp.where(stream_mask_i8 == 0, cp.nan, order)
return order
# =====================================================================
# CPU tile kernels for dask
# =====================================================================
@ngjit
def _strahler_tile_kernel(flow_dir, stream_mask, h, w,
seed_max_top, seed_cnt_top,
seed_max_bottom, seed_cnt_bottom,
seed_max_left, seed_cnt_left,
seed_max_right, seed_cnt_right):
"""Seeded Strahler BFS for a single tile."""
order = np.empty((h, w), dtype=np.float64)
in_degree = np.zeros((h, w), dtype=np.int32)
max_in = np.zeros((h, w), dtype=np.float64)
cnt_max = np.zeros((h, w), dtype=np.int32)
for r in range(h):
for c in range(w):
if stream_mask[r, c] == 0:
order[r, c] = np.nan
else:
order[r, c] = 0.0
# Apply seeds: set max_in / cnt_max from boundary info
for c in range(w):
if stream_mask[0, c] == 1 and seed_max_top[c] > 0:
if seed_max_top[c] > max_in[0, c]:
max_in[0, c] = seed_max_top[c]
cnt_max[0, c] = int(seed_cnt_top[c])
elif seed_max_top[c] == max_in[0, c]:
cnt_max[0, c] += int(seed_cnt_top[c])
if stream_mask[h - 1, c] == 1 and seed_max_bottom[c] > 0:
if seed_max_bottom[c] > max_in[h - 1, c]:
max_in[h - 1, c] = seed_max_bottom[c]
cnt_max[h - 1, c] = int(seed_cnt_bottom[c])
elif seed_max_bottom[c] == max_in[h - 1, c]:
cnt_max[h - 1, c] += int(seed_cnt_bottom[c])
for r in range(h):
if stream_mask[r, 0] == 1 and seed_max_left[r] > 0:
if seed_max_left[r] > max_in[r, 0]:
max_in[r, 0] = seed_max_left[r]
cnt_max[r, 0] = int(seed_cnt_left[r])
elif seed_max_left[r] == max_in[r, 0]:
cnt_max[r, 0] += int(seed_cnt_left[r])
if stream_mask[r, w - 1] == 1 and seed_max_right[r] > 0:
if seed_max_right[r] > max_in[r, w - 1]:
max_in[r, w - 1] = seed_max_right[r]
cnt_max[r, w - 1] = int(seed_cnt_right[r])
elif seed_max_right[r] == max_in[r, w - 1]:
cnt_max[r, w - 1] += int(seed_cnt_right[r])
# Compute in-degrees among stream cells within tile
for r in range(h):
for c in range(w):
if stream_mask[r, c] == 0:
continue
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if 0 <= nr < h and 0 <= nc < w and stream_mask[nr, nc] == 1:
in_degree[nr, nc] += 1
# BFS
queue_r = np.empty(h * w, dtype=np.int64)
queue_c = np.empty(h * w, dtype=np.int64)
head = np.int64(0)
tail = np.int64(0)
for r in range(h):
for c in range(w):
if stream_mask[r, c] != 1:
continue
if in_degree[r, c] != 0:
continue
# Headwater or seeded cell
if max_in[r, c] > 0:
if cnt_max[r, c] >= 2:
order[r, c] = max_in[r, c] + 1.0
else:
order[r, c] = max_in[r, c]
else:
order[r, c] = 1.0
queue_r[tail] = r
queue_c[tail] = c
tail += 1
while head < tail:
r = queue_r[head]
c = queue_c[head]
head += 1
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if not (0 <= nr < h and 0 <= nc < w and stream_mask[nr, nc] == 1):
continue
cur_ord = order[r, c]
if cur_ord > max_in[nr, nc]:
max_in[nr, nc] = cur_ord
cnt_max[nr, nc] = 1
elif cur_ord == max_in[nr, nc]:
cnt_max[nr, nc] += 1
in_degree[nr, nc] -= 1
if in_degree[nr, nc] == 0:
if cnt_max[nr, nc] >= 2:
order[nr, nc] = max_in[nr, nc] + 1.0
else:
order[nr, nc] = max_in[nr, nc]
queue_r[tail] = nr
queue_c[tail] = nc
tail += 1
return order
@ngjit
def _shreve_tile_kernel(flow_dir, stream_mask, h, w,
seed_top, seed_bottom, seed_left, seed_right):
"""Seeded Shreve BFS for a single tile."""
order = np.empty((h, w), dtype=np.float64)
in_degree = np.zeros((h, w), dtype=np.int32)
for r in range(h):
for c in range(w):
if stream_mask[r, c] == 0:
order[r, c] = np.nan
else:
order[r, c] = 0.0
# Apply additive seeds
for c in range(w):
if stream_mask[0, c] == 1:
order[0, c] += seed_top[c]
if stream_mask[h - 1, c] == 1:
order[h - 1, c] += seed_bottom[c]
for r in range(h):
if stream_mask[r, 0] == 1:
order[r, 0] += seed_left[r]
if stream_mask[r, w - 1] == 1:
order[r, w - 1] += seed_right[r]
# In-degrees
for r in range(h):
for c in range(w):
if stream_mask[r, c] == 0:
continue
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if 0 <= nr < h and 0 <= nc < w and stream_mask[nr, nc] == 1:
in_degree[nr, nc] += 1
queue_r = np.empty(h * w, dtype=np.int64)
queue_c = np.empty(h * w, dtype=np.int64)
head = np.int64(0)
tail = np.int64(0)
for r in range(h):
for c in range(w):
if stream_mask[r, c] == 1 and in_degree[r, c] == 0:
if order[r, c] == 0.0:
order[r, c] = 1.0 # headwater
queue_r[tail] = r
queue_c[tail] = c
tail += 1
while head < tail:
r = queue_r[head]
c = queue_c[head]
head += 1
v = flow_dir[r, c]
if v != v:
continue
dy, dx = _code_to_offset(v)
if dy == 0 and dx == 0:
continue
nr = r + dy
nc = c + dx
if not (0 <= nr < h and 0 <= nc < w and stream_mask[nr, nc] == 1):
continue
order[nr, nc] += order[r, c]
in_degree[nr, nc] -= 1
if in_degree[nr, nc] == 0:
queue_r[tail] = nr
queue_c[tail] = nc
tail += 1
return order
# =====================================================================
# Dask iterative tile sweep
# =====================================================================
def _preprocess_stream_tiles(flow_dir_da, accum_da, threshold,
chunks_y, chunks_x):
"""Extract boundary strips for flow dir and stream mask."""
n_tile_y = len(chunks_y)
n_tile_x = len(chunks_x)
flow_bdry = BoundaryStore(chunks_y, chunks_x, fill_value=np.nan)
mask_bdry = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
for iy in range(n_tile_y):
for ix in range(n_tile_x):
fd_chunk = _to_numpy_f64(
flow_dir_da.blocks[iy, ix].compute())
ac_chunk = _to_numpy_f64(
accum_da.blocks[iy, ix].compute())
sm = np.where(ac_chunk >= threshold, 1.0, 0.0)
sm = np.where(np.isnan(ac_chunk), 0.0, sm)
sm = np.where(np.isnan(fd_chunk), 0.0, sm)
for side, row_data_fd, row_data_sm in [
('top', fd_chunk[0, :], sm[0, :]),
('bottom', fd_chunk[-1, :], sm[-1, :]),
('left', fd_chunk[:, 0], sm[:, 0]),
('right', fd_chunk[:, -1], sm[:, -1]),
]:
flow_bdry.set(side, iy, ix,
np.asarray(row_data_fd, dtype=np.float64))
mask_bdry.set(side, iy, ix,
np.asarray(row_data_sm, dtype=np.float64))
return flow_bdry, mask_bdry
def _compute_shreve_seeds(iy, ix, boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x):
"""Compute additive Shreve seeds from neighbours (same as flow_accum)."""
tile_h = chunks_y[iy]
tile_w = chunks_x[ix]
seed_top = np.zeros(tile_w, dtype=np.float64)
seed_bottom = np.zeros(tile_w, dtype=np.float64)
seed_left = np.zeros(tile_h, dtype=np.float64)
seed_right = np.zeros(tile_h, dtype=np.float64)
# Top edge: bottom of tile above
if iy > 0:
nb_fdir = flow_bdry.get('bottom', iy - 1, ix)
nb_mask = mask_bdry.get('bottom', iy - 1, ix)
nb_order = boundaries.get('bottom', iy - 1, ix)
w = len(nb_fdir)
for j in range(w):
if nb_mask[j] == 0:
continue
code = int(nb_fdir[j])
dy, dx = _code_to_offset_py(code)
if dy == 1 and dx == 0 and j < tile_w: # S
seed_top[j] += nb_order[j]
elif dy == 1 and dx == 1 and j + 1 < tile_w: # SE
seed_top[j + 1] += nb_order[j]
elif dy == 1 and dx == -1 and j - 1 >= 0: # SW
seed_top[j - 1] += nb_order[j]
# Bottom edge: top of tile below
if iy < n_tile_y - 1:
nb_fdir = flow_bdry.get('top', iy + 1, ix)
nb_mask = mask_bdry.get('top', iy + 1, ix)
nb_order = boundaries.get('top', iy + 1, ix)
w = len(nb_fdir)
for j in range(w):
if nb_mask[j] == 0:
continue
code = int(nb_fdir[j])
dy, dx = _code_to_offset_py(code)
if dy == -1 and dx == 0 and j < tile_w: # N
seed_bottom[j] += nb_order[j]
elif dy == -1 and dx == 1 and j + 1 < tile_w: # NE
seed_bottom[j + 1] += nb_order[j]
elif dy == -1 and dx == -1 and j - 1 >= 0: # NW
seed_bottom[j - 1] += nb_order[j]
# Left edge: right column of tile to the left
if ix > 0:
nb_fdir = flow_bdry.get('right', iy, ix - 1)
nb_mask = mask_bdry.get('right', iy, ix - 1)
nb_order = boundaries.get('right', iy, ix - 1)
h = len(nb_fdir)
for i in range(h):
if nb_mask[i] == 0:
continue
code = int(nb_fdir[i])
dy, dx = _code_to_offset_py(code)
if dx == 1 and dy == 0 and i < tile_h: # E
seed_left[i] += nb_order[i]
elif dx == 1 and dy == 1 and i + 1 < tile_h: # SE
seed_left[i + 1] += nb_order[i]
elif dx == 1 and dy == -1 and i - 1 >= 0: # NE
seed_left[i - 1] += nb_order[i]
# Right edge: left column of tile to the right
if ix < n_tile_x - 1:
nb_fdir = flow_bdry.get('left', iy, ix + 1)
nb_mask = mask_bdry.get('left', iy, ix + 1)
nb_order = boundaries.get('left', iy, ix + 1)
h = len(nb_fdir)
for i in range(h):
if nb_mask[i] == 0:
continue
code = int(nb_fdir[i])
dy, dx = _code_to_offset_py(code)
if dx == -1 and dy == 0 and i < tile_h: # W
seed_right[i] += nb_order[i]
elif dx == -1 and dy == 1 and i + 1 < tile_h: # SW
seed_right[i + 1] += nb_order[i]
elif dx == -1 and dy == -1 and i - 1 >= 0: # NW
seed_right[i - 1] += nb_order[i]
# Corner seeds from diagonal neighbours
if iy > 0 and ix > 0:
fdir = flow_bdry.get('bottom', iy - 1, ix - 1)[-1]
mask = mask_bdry.get('bottom', iy - 1, ix - 1)[-1]
if mask == 1 and int(fdir) == 2: # SE
seed_top[0] += boundaries.get('bottom', iy - 1, ix - 1)[-1]
if iy > 0 and ix < n_tile_x - 1:
fdir = flow_bdry.get('bottom', iy - 1, ix + 1)[0]
mask = mask_bdry.get('bottom', iy - 1, ix + 1)[0]
if mask == 1 and int(fdir) == 8: # SW
seed_top[tile_w - 1] += boundaries.get(
'bottom', iy - 1, ix + 1)[0]
if iy < n_tile_y - 1 and ix > 0:
fdir = flow_bdry.get('top', iy + 1, ix - 1)[-1]
mask = mask_bdry.get('top', iy + 1, ix - 1)[-1]
if mask == 1 and int(fdir) == 128: # NE
seed_bottom[0] += boundaries.get('top', iy + 1, ix - 1)[-1]
if iy < n_tile_y - 1 and ix < n_tile_x - 1:
fdir = flow_bdry.get('top', iy + 1, ix + 1)[0]
mask = mask_bdry.get('top', iy + 1, ix + 1)[0]
if mask == 1 and int(fdir) == 32: # NW
seed_bottom[tile_w - 1] += boundaries.get(
'top', iy + 1, ix + 1)[0]
return seed_top, seed_bottom, seed_left, seed_right
def _compute_strahler_seeds(iy, ix, bdry_max, bdry_cnt,
flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x):
"""Compute Strahler (max, cnt) seeds from neighbours."""
tile_h = chunks_y[iy]
tile_w = chunks_x[ix]
smax_top = np.zeros(tile_w, dtype=np.float64)
scnt_top = np.zeros(tile_w, dtype=np.float64)
smax_bottom = np.zeros(tile_w, dtype=np.float64)
scnt_bottom = np.zeros(tile_w, dtype=np.float64)
smax_left = np.zeros(tile_h, dtype=np.float64)
scnt_left = np.zeros(tile_h, dtype=np.float64)
smax_right = np.zeros(tile_h, dtype=np.float64)
scnt_right = np.zeros(tile_h, dtype=np.float64)
def _update_max_cnt(cur_max, cur_cnt, new_val, idx):
if new_val > cur_max[idx]:
cur_max[idx] = new_val
cur_cnt[idx] = 1.0
elif new_val == cur_max[idx] and new_val > 0:
cur_cnt[idx] += 1.0
# Top edge
if iy > 0:
nb_fdir = flow_bdry.get('bottom', iy - 1, ix)
nb_mask = mask_bdry.get('bottom', iy - 1, ix)
nb_max = bdry_max.get('bottom', iy - 1, ix)
nb_cnt = bdry_cnt.get('bottom', iy - 1, ix)
w = len(nb_fdir)
for j in range(w):
if nb_mask[j] == 0 or nb_max[j] == 0:
continue
code = int(nb_fdir[j])
dy, dx = _code_to_offset_py(code)
target = -1
if dy == 1 and dx == 0:
target = j
elif dy == 1 and dx == 1:
target = j + 1
elif dy == 1 and dx == -1:
target = j - 1
if 0 <= target < tile_w:
# Reconstruct the order that this cell had
if nb_cnt[j] >= 2:
val = nb_max[j] + 1.0
else:
val = nb_max[j]
_update_max_cnt(smax_top, scnt_top, val, target)
# Bottom edge
if iy < n_tile_y - 1:
nb_fdir = flow_bdry.get('top', iy + 1, ix)
nb_mask = mask_bdry.get('top', iy + 1, ix)
nb_max = bdry_max.get('top', iy + 1, ix)
nb_cnt = bdry_cnt.get('top', iy + 1, ix)
w = len(nb_fdir)
for j in range(w):
if nb_mask[j] == 0 or nb_max[j] == 0:
continue
code = int(nb_fdir[j])
dy, dx = _code_to_offset_py(code)
target = -1
if dy == -1 and dx == 0:
target = j
elif dy == -1 and dx == 1:
target = j + 1
elif dy == -1 and dx == -1:
target = j - 1
if 0 <= target < tile_w:
if nb_cnt[j] >= 2:
val = nb_max[j] + 1.0
else:
val = nb_max[j]
_update_max_cnt(smax_bottom, scnt_bottom, val, target)
# Left edge
if ix > 0:
nb_fdir = flow_bdry.get('right', iy, ix - 1)
nb_mask = mask_bdry.get('right', iy, ix - 1)
nb_max = bdry_max.get('right', iy, ix - 1)
nb_cnt = bdry_cnt.get('right', iy, ix - 1)
h = len(nb_fdir)
for i in range(h):
if nb_mask[i] == 0 or nb_max[i] == 0:
continue
code = int(nb_fdir[i])
dy, dx = _code_to_offset_py(code)
target = -1
if dx == 1 and dy == 0:
target = i
elif dx == 1 and dy == 1:
target = i + 1
elif dx == 1 and dy == -1:
target = i - 1
if 0 <= target < tile_h:
if nb_cnt[i] >= 2:
val = nb_max[i] + 1.0
else:
val = nb_max[i]
_update_max_cnt(smax_left, scnt_left, val, target)
# Right edge
if ix < n_tile_x - 1:
nb_fdir = flow_bdry.get('left', iy, ix + 1)
nb_mask = mask_bdry.get('left', iy, ix + 1)
nb_max = bdry_max.get('left', iy, ix + 1)
nb_cnt = bdry_cnt.get('left', iy, ix + 1)
h = len(nb_fdir)
for i in range(h):
if nb_mask[i] == 0 or nb_max[i] == 0:
continue
code = int(nb_fdir[i])
dy, dx = _code_to_offset_py(code)
target = -1
if dx == -1 and dy == 0:
target = i
elif dx == -1 and dy == 1:
target = i + 1
elif dx == -1 and dy == -1:
target = i - 1
if 0 <= target < tile_h:
if nb_cnt[i] >= 2:
val = nb_max[i] + 1.0
else:
val = nb_max[i]
_update_max_cnt(smax_right, scnt_right, val, target)
# Corners
def _corner_seed(nb_side, nb_iy, nb_ix, nb_idx, code_expected,
s_max, s_cnt, target):
fdir = flow_bdry.get(nb_side, nb_iy, nb_ix)[nb_idx]
mask = mask_bdry.get(nb_side, nb_iy, nb_ix)[nb_idx]
if mask == 1 and int(fdir) == code_expected:
nm = bdry_max.get(nb_side, nb_iy, nb_ix)[nb_idx]
nc = bdry_cnt.get(nb_side, nb_iy, nb_ix)[nb_idx]
if nm > 0:
val = nm + 1.0 if nc >= 2 else nm
_update_max_cnt(s_max, s_cnt, val, target)
if iy > 0 and ix > 0:
_corner_seed('bottom', iy - 1, ix - 1, -1, 2,
smax_top, scnt_top, 0)
if iy > 0 and ix < n_tile_x - 1:
_corner_seed('bottom', iy - 1, ix + 1, 0, 8,
smax_top, scnt_top, tile_w - 1)
if iy < n_tile_y - 1 and ix > 0:
_corner_seed('top', iy + 1, ix - 1, -1, 128,
smax_bottom, scnt_bottom, 0)
if iy < n_tile_y - 1 and ix < n_tile_x - 1:
_corner_seed('top', iy + 1, ix + 1, 0, 32,
smax_bottom, scnt_bottom, tile_w - 1)
return (smax_top, scnt_top, smax_bottom, scnt_bottom,
smax_left, scnt_left, smax_right, scnt_right)
def _process_strahler_tile(iy, ix, flow_dir_da, accum_da, threshold,
bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x):
"""Run seeded Strahler BFS on one tile; update boundary stores."""
fd_chunk = np.asarray(
flow_dir_da.blocks[iy, ix].compute(), dtype=np.float64)
ac_chunk = np.asarray(
accum_da.blocks[iy, ix].compute(), dtype=np.float64)
sm = np.where(ac_chunk >= threshold, 1, 0).astype(np.int8)
sm = np.where(np.isnan(ac_chunk), 0, sm).astype(np.int8)
sm = np.where(np.isnan(fd_chunk), 0, sm).astype(np.int8)
h, w = fd_chunk.shape
seeds = _compute_strahler_seeds(
iy, ix, bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
order = _strahler_tile_kernel(fd_chunk, sm, h, w, *seeds)
# Extract boundary order values and recompute max/cnt for boundaries
change = 0.0
for side, strip in [('top', order[0, :]),
('bottom', order[-1, :]),
('left', order[:, 0]),
('right', order[:, -1])]:
new_vals = strip.copy()
# For Strahler boundaries we store the raw order value as max,
# with cnt=1 (represents the cell's own order for seed computation).
# The seed computation will use these as incoming orders.
new_max = np.where(np.isnan(new_vals), 0.0, new_vals)
new_cnt = np.where(new_max > 0, 1.0, 0.0)
old_max = bdry_max.get(side, iy, ix).copy()
with np.errstate(invalid='ignore'):
diff = np.abs(new_max - old_max)
diff = np.where(np.isnan(diff), 0.0, diff)
m = float(np.max(diff))
if m > change:
change = m
bdry_max.set(side, iy, ix, new_max)
bdry_cnt.set(side, iy, ix, new_cnt)
return change
def _process_shreve_tile(iy, ix, flow_dir_da, accum_da, threshold,
boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x):
"""Run seeded Shreve BFS on one tile; update boundaries."""
fd_chunk = np.asarray(
flow_dir_da.blocks[iy, ix].compute(), dtype=np.float64)
ac_chunk = np.asarray(
accum_da.blocks[iy, ix].compute(), dtype=np.float64)
sm = np.where(ac_chunk >= threshold, 1, 0).astype(np.int8)
sm = np.where(np.isnan(ac_chunk), 0, sm).astype(np.int8)
sm = np.where(np.isnan(fd_chunk), 0, sm).astype(np.int8)
h, w = fd_chunk.shape
seeds = _compute_shreve_seeds(
iy, ix, boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
order = _shreve_tile_kernel(fd_chunk, sm, h, w, *seeds)
change = 0.0
for side, strip in [('top', order[0, :]),
('bottom', order[-1, :]),
('left', order[:, 0]),
('right', order[:, -1])]:
new_vals = strip.copy()
new_vals = np.where(np.isnan(new_vals), 0.0, new_vals)
old = boundaries.get(side, iy, ix).copy()
with np.errstate(invalid='ignore'):
diff = np.abs(new_vals - old)
diff = np.where(np.isnan(diff), 0.0, diff)
m = float(np.max(diff))
if m > change:
change = m
boundaries.set(side, iy, ix, new_vals)
return change
def _stream_order_dask_strahler(flow_dir_da, accum_da, threshold):
"""Dask iterative sweep for Strahler ordering."""
chunks_y = flow_dir_da.chunks[0]
chunks_x = flow_dir_da.chunks[1]
n_tile_y = len(chunks_y)
n_tile_x = len(chunks_x)
flow_bdry, mask_bdry = _preprocess_stream_tiles(
flow_dir_da, accum_da, threshold, chunks_y, chunks_x)
# Read-only from here; release temp files
flow_bdry = flow_bdry.snapshot()
mask_bdry = mask_bdry.snapshot()
bdry_max = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
bdry_cnt = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
max_iterations = max(n_tile_y, n_tile_x) + 10
for _ in range(max_iterations):
max_change = 0.0
for iy in range(n_tile_y):
for ix in range(n_tile_x):
c = _process_strahler_tile(
iy, ix, flow_dir_da, accum_da, threshold,
bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
for iy in reversed(range(n_tile_y)):
for ix in reversed(range(n_tile_x)):
c = _process_strahler_tile(
iy, ix, flow_dir_da, accum_da, threshold,
bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
if max_change == 0.0:
break
# Snapshot converged boundaries before assembly (releases temp files)
_bdry_max = bdry_max.snapshot()
_bdry_cnt = bdry_cnt.snapshot()
_flow_bdry = flow_bdry
_mask_bdry = mask_bdry
_threshold = threshold
def _tile_fn(block, accum_block, block_info=None):
if block_info is None or 0 not in block_info:
return np.full(block.shape, np.nan, dtype=np.float64)
iy, ix = block_info[0]['chunk-location']
fd = np.asarray(block, dtype=np.float64)
ac = np.asarray(accum_block, dtype=np.float64)
sm = np.where(ac >= _threshold, 1, 0).astype(np.int8)
sm = np.where(np.isnan(ac), 0, sm).astype(np.int8)
sm = np.where(np.isnan(fd), 0, sm).astype(np.int8)
h, w = fd.shape
seeds = _compute_strahler_seeds(
iy, ix, _bdry_max, _bdry_cnt, _flow_bdry, _mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
return _strahler_tile_kernel(fd, sm, h, w, *seeds)
return da.map_blocks(
_tile_fn, flow_dir_da, accum_da,
dtype=np.float64, meta=np.array((), dtype=np.float64))
def _stream_order_dask_shreve(flow_dir_da, accum_da, threshold):
"""Dask iterative sweep for Shreve ordering."""
chunks_y = flow_dir_da.chunks[0]
chunks_x = flow_dir_da.chunks[1]
n_tile_y = len(chunks_y)
n_tile_x = len(chunks_x)
flow_bdry, mask_bdry = _preprocess_stream_tiles(
flow_dir_da, accum_da, threshold, chunks_y, chunks_x)
# Read-only from here; release temp files
flow_bdry = flow_bdry.snapshot()
mask_bdry = mask_bdry.snapshot()
boundaries = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
max_iterations = max(n_tile_y, n_tile_x) + 10
for _ in range(max_iterations):
max_change = 0.0
for iy in range(n_tile_y):
for ix in range(n_tile_x):
c = _process_shreve_tile(
iy, ix, flow_dir_da, accum_da, threshold,
boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
for iy in reversed(range(n_tile_y)):
for ix in reversed(range(n_tile_x)):
c = _process_shreve_tile(
iy, ix, flow_dir_da, accum_da, threshold,
boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
if max_change == 0.0:
break
# Snapshot converged boundaries before assembly (releases temp files)
_boundaries = boundaries.snapshot()
_flow_bdry = flow_bdry
_mask_bdry = mask_bdry
_threshold = threshold
def _tile_fn(block, accum_block, block_info=None):
if block_info is None or 0 not in block_info:
return np.full(block.shape, np.nan, dtype=np.float64)
iy, ix = block_info[0]['chunk-location']
fd = np.asarray(block, dtype=np.float64)
ac = np.asarray(accum_block, dtype=np.float64)
sm = np.where(ac >= _threshold, 1, 0).astype(np.int8)
sm = np.where(np.isnan(ac), 0, sm).astype(np.int8)
sm = np.where(np.isnan(fd), 0, sm).astype(np.int8)
h, w = fd.shape
seeds = _compute_shreve_seeds(
iy, ix, _boundaries, _flow_bdry, _mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
return _shreve_tile_kernel(fd, sm, h, w, *seeds)
return da.map_blocks(
_tile_fn, flow_dir_da, accum_da,
dtype=np.float64, meta=np.array((), dtype=np.float64))
def _stream_order_tile_cupy(flow_dir_data, stream_mask_data, method,
seeds):
"""GPU seeded stream order for a single tile.
Uses GPU frontier peeling with seeds injected after initialisation.
For Strahler, seeds are (max_top, cnt_top, max_bot, cnt_bot, ...).
For Shreve, seeds are (top, bot, left, right).
"""
import cupy as cp
H, W = flow_dir_data.shape
flow_dir_f64 = flow_dir_data.astype(cp.float64)
stream_mask_i8 = stream_mask_data.astype(cp.int8)
in_degree = cp.zeros((H, W), dtype=cp.int32)
state = cp.zeros((H, W), dtype=cp.int32)
order = cp.zeros((H, W), dtype=cp.float64)
max_in = cp.zeros((H, W), dtype=cp.float64)
cnt_max = cp.zeros((H, W), dtype=cp.int32)
changed = cp.zeros(1, dtype=cp.int32)
griddim, blockdim = cuda_args((H, W))
_stream_order_init_gpu[griddim, blockdim](
flow_dir_f64, stream_mask_i8, in_degree, state,
order, max_in, cnt_max, H, W)
if method == 'strahler':
(smax_top, scnt_top, smax_bot, scnt_bot,
smax_left, scnt_left, smax_right, scnt_right) = seeds
# Inject Strahler seeds at boundaries.
# After init, max_in is 0.0 everywhere. Where seed_max > 0,
# set max_in and cnt_max.
for r_idx, s_max, s_cnt in [
((0, slice(None)), smax_top, scnt_top),
((H - 1, slice(None)), smax_bot, scnt_bot),
((slice(None), 0), smax_left, scnt_left),
((slice(None), W - 1), smax_right, scnt_right),
]:
sm_cp = cp.asarray(s_max)
sc_cp = cp.asarray(s_cnt).astype(cp.int32)
is_stream = stream_mask_i8[r_idx] == 1
has_seed = sm_cp > 0
mask = is_stream & has_seed
# Since max_in starts at 0, seed_max > 0 always wins
max_in[r_idx] = cp.where(mask, sm_cp, max_in[r_idx])
cnt_max[r_idx] = cp.where(mask, sc_cp, cnt_max[r_idx])
else:
(seed_top, seed_bot, seed_left, seed_right) = seeds
# Inject Shreve seeds: additive, same as flow_accumulation
order[0, :] += cp.asarray(seed_top)
order[H - 1, :] += cp.asarray(seed_bot)
order[:, 0] += cp.asarray(seed_left)
order[:, W - 1] += cp.asarray(seed_right)
max_iter = H * W
for _ in range(max_iter):
changed[0] = 0
_stream_order_find_ready[griddim, blockdim](
in_degree, state, order, changed, H, W)
if int(changed[0]) == 0:
break
if method == 'strahler':
_stream_order_pull_strahler[griddim, blockdim](
flow_dir_f64, stream_mask_i8, in_degree, state,
order, max_in, cnt_max, H, W)
else:
_stream_order_pull_shreve[griddim, blockdim](
flow_dir_f64, stream_mask_i8, in_degree, state,
order, H, W)
order = cp.where(stream_mask_i8 == 0, cp.nan, order)
return order
def _make_stream_mask_np(ac_chunk, fd_chunk, threshold):
"""Build stream mask as numpy int8 from accumulation chunk."""
sm = np.where(ac_chunk >= threshold, 1, 0).astype(np.int8)
sm = np.where(np.isnan(ac_chunk), 0, sm).astype(np.int8)
sm = np.where(np.isnan(fd_chunk), 0, sm).astype(np.int8)
return sm
def _process_strahler_tile_cupy(iy, ix, flow_dir_da, accum_da, threshold,
bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x):
"""Run seeded GPU Strahler on one tile; update boundary stores."""
import cupy as cp
fd_chunk = cp.asarray(
flow_dir_da.blocks[iy, ix].compute(), dtype=cp.float64)
ac_chunk = _to_numpy_f64(accum_da.blocks[iy, ix].compute())
fd_np = fd_chunk.get()
sm_np = _make_stream_mask_np(ac_chunk, fd_np, threshold)
sm_cp = cp.asarray(sm_np)
seeds = _compute_strahler_seeds(
iy, ix, bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
order = _stream_order_tile_cupy(fd_chunk, sm_cp, 'strahler', seeds)
change = 0.0
for side, strip_cp in [('top', order[0, :]),
('bottom', order[-1, :]),
('left', order[:, 0]),
('right', order[:, -1])]:
new_vals = strip_cp.get().copy()
new_max = np.where(np.isnan(new_vals), 0.0, new_vals)
new_cnt = np.where(new_max > 0, 1.0, 0.0)
old_max = bdry_max.get(side, iy, ix).copy()
with np.errstate(invalid='ignore'):
diff = np.abs(new_max - old_max)
diff = np.where(np.isnan(diff), 0.0, diff)
m = float(np.max(diff))
if m > change:
change = m
bdry_max.set(side, iy, ix, new_max)
bdry_cnt.set(side, iy, ix, new_cnt)
return change
def _process_shreve_tile_cupy(iy, ix, flow_dir_da, accum_da, threshold,
boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x):
"""Run seeded GPU Shreve on one tile; update boundaries."""
import cupy as cp
fd_chunk = cp.asarray(
flow_dir_da.blocks[iy, ix].compute(), dtype=cp.float64)
ac_chunk = _to_numpy_f64(accum_da.blocks[iy, ix].compute())
fd_np = fd_chunk.get()
sm_np = _make_stream_mask_np(ac_chunk, fd_np, threshold)
sm_cp = cp.asarray(sm_np)
seeds = _compute_shreve_seeds(
iy, ix, boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
order = _stream_order_tile_cupy(fd_chunk, sm_cp, 'shreve', seeds)
change = 0.0
for side, strip_cp in [('top', order[0, :]),
('bottom', order[-1, :]),
('left', order[:, 0]),
('right', order[:, -1])]:
new_vals = strip_cp.get().copy()
new_vals = np.where(np.isnan(new_vals), 0.0, new_vals)
old = boundaries.get(side, iy, ix).copy()
with np.errstate(invalid='ignore'):
diff = np.abs(new_vals - old)
diff = np.where(np.isnan(diff), 0.0, diff)
m = float(np.max(diff))
if m > change:
change = m
boundaries.set(side, iy, ix, new_vals)
return change
def _stream_order_dask_cupy(flow_dir_da, accum_da, threshold, method):
"""Dask+CuPy: native GPU processing per tile."""
import cupy as cp
chunks_y = flow_dir_da.chunks[0]
chunks_x = flow_dir_da.chunks[1]
n_tile_y = len(chunks_y)
n_tile_x = len(chunks_x)
flow_bdry, mask_bdry = _preprocess_stream_tiles(
flow_dir_da, accum_da, threshold, chunks_y, chunks_x)
flow_bdry = flow_bdry.snapshot()
mask_bdry = mask_bdry.snapshot()
max_iterations = max(n_tile_y, n_tile_x) + 10
if method == 'strahler':
bdry_max = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
bdry_cnt = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
for _ in range(max_iterations):
max_change = 0.0
for iy in range(n_tile_y):
for ix in range(n_tile_x):
c = _process_strahler_tile_cupy(
iy, ix, flow_dir_da, accum_da, threshold,
bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
for iy in reversed(range(n_tile_y)):
for ix in reversed(range(n_tile_x)):
c = _process_strahler_tile_cupy(
iy, ix, flow_dir_da, accum_da, threshold,
bdry_max, bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
if max_change == 0.0:
break
_bdry_max = bdry_max.snapshot()
_bdry_cnt = bdry_cnt.snapshot()
def _tile_fn(block, accum_block, block_info=None):
if block_info is None or 0 not in block_info:
return cp.full(block.shape, cp.nan, dtype=cp.float64)
iy, ix = block_info[0]['chunk-location']
fd = cp.asarray(block, dtype=cp.float64)
ac_np = _to_numpy_f64(accum_block)
fd_np = fd.get()
sm = cp.asarray(_make_stream_mask_np(ac_np, fd_np, threshold))
seeds = _compute_strahler_seeds(
iy, ix, _bdry_max, _bdry_cnt, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
return _stream_order_tile_cupy(fd, sm, 'strahler', seeds)
else: # shreve
boundaries = BoundaryStore(chunks_y, chunks_x, fill_value=0.0)
for _ in range(max_iterations):
max_change = 0.0
for iy in range(n_tile_y):
for ix in range(n_tile_x):
c = _process_shreve_tile_cupy(
iy, ix, flow_dir_da, accum_da, threshold,
boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
for iy in reversed(range(n_tile_y)):
for ix in reversed(range(n_tile_x)):
c = _process_shreve_tile_cupy(
iy, ix, flow_dir_da, accum_da, threshold,
boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
if c > max_change:
max_change = c
if max_change == 0.0:
break
_boundaries = boundaries.snapshot()
def _tile_fn(block, accum_block, block_info=None):
if block_info is None or 0 not in block_info:
return cp.full(block.shape, cp.nan, dtype=cp.float64)
iy, ix = block_info[0]['chunk-location']
fd = cp.asarray(block, dtype=cp.float64)
ac_np = _to_numpy_f64(accum_block)
fd_np = fd.get()
sm = cp.asarray(_make_stream_mask_np(ac_np, fd_np, threshold))
seeds = _compute_shreve_seeds(
iy, ix, _boundaries, flow_bdry, mask_bdry,
chunks_y, chunks_x, n_tile_y, n_tile_x)
return _stream_order_tile_cupy(fd, sm, 'shreve', seeds)
return da.map_blocks(
_tile_fn, flow_dir_da, accum_da,
dtype=np.float64, meta=cp.array((), dtype=cp.float64))
# =====================================================================
# Public API
# =====================================================================
[docs]
@supports_dataset
def stream_order_d8(flow_dir: xr.DataArray,
flow_accum: xr.DataArray,
threshold: float = 100,
ordering: str = 'strahler',
name: str = 'stream_order',
method: str | None = None) -> xr.DataArray:
"""Compute stream order from D8 flow direction and accumulation grids.
Parameters
----------
flow_dir : xarray.DataArray or xr.Dataset
2D D8 flow direction grid (codes 0/1/2/4/8/16/32/64/128;
NaN for nodata).
flow_accum : xarray.DataArray
2D flow accumulation grid. Cells with
``flow_accum >= threshold`` are considered stream cells.
threshold : float, default 100
Minimum accumulation to classify a cell as part of the
stream network.
ordering : str, default 'strahler'
``'strahler'`` for Strahler branching hierarchy or
``'shreve'`` for Shreve cumulative magnitude.
name : str, default 'stream_order'
Name of output DataArray.
method : str, optional
Alias for ``ordering``, accepted for consistency with
``stream_order_dinf`` and ``stream_order_mfd``, which name this
parameter ``method``. If given, it takes precedence over
``ordering``. Passing both with conflicting values raises
``ValueError``.
Returns
-------
xarray.DataArray or xr.Dataset
2D float64 array of stream order values. Non-stream cells
(accumulation below threshold) are NaN.
References
----------
Strahler, A.N. (1957). Quantitative analysis of watershed
geomorphology. Transactions of the American Geophysical Union,
38(6), 913-920.
Shreve, R.L. (1966). Statistical law of stream numbers. Journal
of Geology, 74(1), 17-37.
"""
_validate_raster(flow_dir, func_name='stream_order', name='flow_dir')
_validate_raster(flow_accum, func_name='stream_order', name='flow_accum')
# `method` is an alias for `ordering` (parity with the dinf/mfd
# variants). Compare case-insensitively, and only treat them as
# conflicting when the caller set `ordering` to a non-default value
# that differs from `method`.
if (method is not None
and ordering.lower() != 'strahler'
and method.lower() != ordering.lower()):
raise ValueError(
f"Pass either 'ordering' or 'method', not both with different "
f"values (got ordering={ordering!r}, method={method!r})")
selected = method if method is not None else ordering
method = selected.lower()
if method not in ('strahler', 'shreve'):
raise ValueError(
f"ordering must be 'strahler' or 'shreve', got {selected!r}")
fd_data = flow_dir.data
fa_data = flow_accum.data
if isinstance(fd_data, np.ndarray):
_check_memory(*fd_data.shape)
fd = fd_data.astype(np.float64)
fa = np.asarray(fa_data, dtype=np.float64)
stream_mask = np.where(fa >= threshold, 1, 0).astype(np.int8)
stream_mask = np.where(np.isnan(fa), 0, stream_mask).astype(np.int8)
# NaN flow_dir → not stream
stream_mask = np.where(np.isnan(fd), 0, stream_mask).astype(np.int8)
h, w = fd.shape
if method == 'strahler':
out = _strahler_cpu(fd, stream_mask, h, w)
else:
out = _shreve_cpu(fd, stream_mask, h, w)
elif has_cuda_and_cupy() and is_cupy_array(fd_data):
_check_gpu_memory(*fd_data.shape)
import cupy as cp
fa_cp = cp.asarray(fa_data, dtype=cp.float64)
fd_cp = fd_data.astype(cp.float64)
stream_mask = cp.where(fa_cp >= threshold, 1, 0).astype(cp.int8)
stream_mask = cp.where(cp.isnan(fa_cp), 0, stream_mask).astype(cp.int8)
stream_mask = cp.where(cp.isnan(fd_cp), 0, stream_mask).astype(cp.int8)
out = _stream_order_cupy(fd_cp, stream_mask, method)
elif has_cuda_and_cupy() and is_dask_cupy(flow_dir):
out = _stream_order_dask_cupy(fd_data, fa_data, threshold, method)
elif da is not None and isinstance(fd_data, da.Array):
if method == 'strahler':
out = _stream_order_dask_strahler(fd_data, fa_data, threshold)
else:
out = _stream_order_dask_shreve(fd_data, fa_data, threshold)
else:
raise TypeError(f"Unsupported array type: {type(fd_data)}")
return xr.DataArray(out,
name=name,
coords=flow_dir.coords,
dims=flow_dir.dims,
attrs=flow_dir.attrs)
