#! /usr/bin/env python
"""Functions to calculate flow distance from divide."""
import numpy as np
from landlab import FieldError
from landlab import RasterModelGrid
[docs]
def calculate_distance_to_divide(
grid, longest_path=True, add_to_grid=False, clobber=False
):
"""Calculate the along flow distance from drainage divide to point.
This utility calculates the along flow distance based on the results of
running flow accumulation on the grid. It will use the connectivity
used by the FlowAccumulator (e.g. D4, D8, Dinf).
Parameters
----------
grid : ModelGrid
longest_path : bool, optional
Take the longest (or shortest) path to a drainage divide. Default is
true.
add_to_grid : boolean, optional
Flag to indicate if the stream length field should be added to the
grid. Default is False. The field name used is ``distance_to_divide``.
clobber : boolean, optional
Flag to indicate if adding the field to the grid should not clobber an
existing field with the same name. Default is False.
Returns
-------
distance_to_divide : float ndarray
The distance that has to be covered from an imaginary flow, located in
each node of the grid, to reach the watershed's outlet.
Examples
--------
>>> import numpy as np
>>> from landlab import RasterModelGrid
>>> from landlab.components import FlowAccumulator
>>> from landlab.utils.distance_to_divide import calculate_distance_to_divide
>>> mg = RasterModelGrid((5, 4))
>>> mg.at_node["topographic__elevation"] = [
... [0.0, 0.0, 0.0, 0.0],
... [0.0, 10.0, 10.0, 0.0],
... [0.0, 20.0, 20.0, 0.0],
... [0.0, 30.0, 30.0, 0.0],
... [0.0, 0.0, 0.0, 0.0],
... ]
>>> mg.set_closed_boundaries_at_grid_edges(
... bottom_is_closed=False,
... left_is_closed=True,
... right_is_closed=True,
... top_is_closed=True,
... )
>>> fr = FlowAccumulator(mg, flow_director="D8")
>>> fr.run_one_step()
>>> distance_to_divide = calculate_distance_to_divide(
... mg,
... add_to_grid=True,
... clobber=True,
... )
>>> mg.at_node["distance_to_divide"]
array([0., 3., 3., 0.,
0., 2., 2., 0.,
0., 1., 1., 0.,
0., 0., 0., 0.,
0., 0., 0., 0.])
Now, let's change to MFD the flow_director method, which routes flow to
multiple nodes.
>>> from landlab import RasterModelGrid
>>> from landlab.components import FlowAccumulator
>>> from landlab.utils.distance_to_divide import calculate_distance_to_divide
>>> mg = RasterModelGrid((5, 4), xy_spacing=(1, 1))
>>> mg.at_node["topographic__elevation"] = [
... [0.0, 0.0, 0.0, 0.0],
... [0.0, 10.0, 10.0, 0.0],
... [0.0, 20.0, 20.0, 0.0],
... [0.0, 30.0, 30.0, 0.0],
... [0.0, 0.0, 0.0, 0.0],
... ]
>>> mg.set_closed_boundaries_at_grid_edges(
... bottom_is_closed=False,
... left_is_closed=True,
... right_is_closed=True,
... top_is_closed=True,
... )
>>> fr = FlowAccumulator(mg, flow_director="MFD")
>>> fr.run_one_step()
>>> distance_to_divide = calculate_distance_to_divide(
... mg,
... add_to_grid=True,
... clobber=True,
... )
>>> mg.at_node["distance_to_divide"]
array([0., 3., 3., 0.,
0., 2., 2., 0.,
0., 1., 1., 0.,
0., 0., 0., 0.,
0., 0., 0., 0.])
The distance_to_divide utility can also work on irregular grids. For the
example we will use a Hexagonal Model Grid, a special type of Voroni Grid
that has regularly spaced hexagonal cells.
>>> from landlab import HexModelGrid
>>> from landlab.components import FlowAccumulator
>>> from landlab.utils.distance_to_divide import calculate_distance_to_divide
>>> dx = 1
>>> hmg = HexModelGrid((5, 3), dx)
>>> _ = hmg.add_field(
... "topographic__elevation",
... hmg.node_x + np.round(hmg.node_y),
... at="node",
... )
>>> hmg.status_at_node[hmg.boundary_nodes] = hmg.BC_NODE_IS_CLOSED
>>> hmg.status_at_node[0] = hmg.BC_NODE_IS_FIXED_VALUE
>>> fr = FlowAccumulator(hmg, flow_director="D4")
>>> fr.run_one_step()
>>> distance_to_divide = calculate_distance_to_divide(
... hmg,
... add_to_grid=True,
... clobber=True,
... )
>>> hmg.at_node["distance_to_divide"]
array([3., 0., 0.,
0., 2., 1., 0.,
0., 1., 1., 0., 0.,
0., 0., 0., 0.,
0., 0., 0.])
"""
# check that flow__receiver nodes exists
if "flow__receiver_node" not in grid.at_node:
raise FieldError(
"A 'flow__receiver_node' field is required at the "
"nodes of the input grid."
)
if "flow__upstream_node_order" not in grid.at_node:
raise FieldError(
"A 'flow__upstream_node_order' field is required at the "
"nodes of the input grid."
)
if "drainage_area" not in grid.at_node:
raise FieldError(
"A 'flow__upstream_node_order' field is required at the "
"nodes of the input grid."
)
# get the reciever nodes, depending on if this is to-one, or to-multiple,
# we'll need to get a different at-node field.
if grid.at_node["flow__receiver_node"].size != grid.size("node"):
to_one = False
else:
to_one = True
flow__receiver_node = grid.at_node["flow__receiver_node"]
drainage_area = grid.at_node["drainage_area"]
# get the upstream node order
flow__upstream_node_order = grid.at_node["flow__upstream_node_order"]
# get downstream flow link lengths, result depends on type of grid.
if isinstance(grid, RasterModelGrid):
flow_link_lengths = grid.length_of_d8[
grid.at_node["flow__link_to_receiver_node"]
]
else:
flow_link_lengths = grid.length_of_link[
grid.at_node["flow__link_to_receiver_node"]
]
# create an array that representes the distance to the divide.
distance_to_divide = np.zeros(grid.nodes.size)
if not longest_path:
distance_to_divide[:] = 2 * grid.size("node") * np.max(flow_link_lengths)
# iterate through the flow__upstream_node_order backwards.
for node in reversed(flow__upstream_node_order):
# if drainage are is equal to node cell area, set distance to zeros
# this should handle the drainage divide cells as boundary cells have
# their area set to zero.
if drainage_area[node] == grid.cell_area_at_node[node]:
distance_to_divide[node] = 0
# get flow recievers
reciever = flow__receiver_node[node]
if to_one:
# if not processing an outlet node.
if reciever != node:
if longest_path:
cond = (
distance_to_divide[reciever]
< distance_to_divide[node] + flow_link_lengths[node]
)
else:
cond = (
distance_to_divide[reciever]
> distance_to_divide[node] + flow_link_lengths[node]
)
if cond:
distance_to_divide[reciever] = (
distance_to_divide[node] + flow_link_lengths[node]
)
else:
# non-existant links are coded with -1
useable_receivers = np.where(reciever != grid.BAD_INDEX)[0]
for idx in range(len(useable_receivers)):
r = reciever[useable_receivers][idx]
fll = flow_link_lengths[node][useable_receivers][idx]
# if not processing an outlet node.
if r != node:
if longest_path:
cond = distance_to_divide[r] < distance_to_divide[node] + fll
else:
cond = distance_to_divide[r] > distance_to_divide[node] + fll
if cond:
distance_to_divide[r] = distance_to_divide[node] + fll
# store on the grid
if add_to_grid:
grid.add_field(
"distance_to_divide", distance_to_divide, at="node", clobber=clobber
)
return distance_to_divide