def test_scalar_arg():
grad = rfuncs.calculate_steepest_descent_across_cell_faces(
_GRID, _VALUES_AT_NODES, 0)
assert_equal(grad, -5.)
grad = _GRID.calculate_steepest_descent_across_cell_faces(_VALUES_AT_NODES, 0)
assert_equal(grad, -5.)
def test_scalar_arg():
grad = rfuncs.calculate_steepest_descent_across_cell_faces(
_GRID, _VALUES_AT_NODES, 0)
assert_equal(grad, -5.)
grad = _GRID.calculate_steepest_descent_across_cell_faces(_VALUES_AT_NODES, 0)
assert_equal(grad, -5.)
def test_iterable():
grad = rfuncs.calculate_steepest_descent_across_cell_faces(
_GRID, _VALUES_AT_NODES, [0, 4])
assert_array_equal(grad, [-5., -5.])
grad = _GRID.calculate_steepest_descent_across_cell_faces(
_VALUES_AT_NODES, [0, 4])
assert_array_equal(grad, [-5., -5.])
def test_iterable():
grad = rfuncs.calculate_steepest_descent_across_cell_faces(
_GRID, _VALUES_AT_NODES, [0, 4])
assert_array_equal(grad, [-5., -5.])
grad = _GRID.calculate_steepest_descent_across_cell_faces(
_VALUES_AT_NODES, [0, 4])
assert_array_equal(grad, [-5., -5.])
def grid_flow_directions(grid, elevations):
"""Flow directions on raster grid.
Calculate flow directions for node elevations on a raster grid.
Each node is assigned a single direction, toward one of its neighboring
nodes (or itself, if none of its neighbors are lower). There is only
flow from one node to another if there is a negative gradient. If a
node's steepest gradient is >= 0., then its slope is set to zero and
its receiver node is listed as itself.
Parameters
----------
grid : RasterModelGrid
a raster grid.
elevations: ndarray
Node elevations.
Returns
-------
receiver : (ncells, ) ndarray
For each cell, the node in the direction of steepest descent, or
itself if no downstream nodes.
steepest_slope : (ncells, ) ndarray
The slope value in the steepest direction of flow.
Notes
-----
This function considers only nodes that have four neighbors. Thus, only
calculate flow directions and slopes for nodes that have associated
cells.
Examples
--------
This example calculates flow routing on a (4,5) raster grid with the
following node elevations::
5 - 5 - 5 - 5 - 5
| | | | |
5 - 3 - 4 - 3 - 5
| | | | |
5 - 1 - 2 - 2 - 5
| | | | |
5 - 0 - 5 - 5 - 5
>>> import numpy as np
>>> from landlab import RasterModelGrid
>>> from landlab.components.flow_routing.flow_direction_DN import grid_flow_directions
>>> mg = RasterModelGrid(4,5)
>>> z = np.array([5., 0., 5., 5., 5.,
... 5., 1., 2., 2., 5.,
... 5., 3., 4., 3., 5.,
... 5., 5., 5., 5., 5.])
>>> recv_nodes, slope = grid_flow_directions(mg, z)
Each node with a cell has a receiving node (although that node may be
itself).
>>> recv_nodes
array([1, 6, 8, 6, 7, 8])
All positive gradients are clipped to zero.
>>> slope
array([-1., -1., 0., -2., -2., -1.])
If a cell has no surrounding neighbors lower than itself, it is a sink.
Use :attr:`~landlab.grid.base.ModelGrid.node_index_at_cells` to get the
nodes associated with the cells.
>>> sink_cells = np.where(slope >= 0)[0]
>>> sink_cells
array([2])
>>> mg.node_index_at_cells[sink_cells] # Sink nodes
array([8])
The source/destination node pairs for the flow.
>>> zip(mg.node_index_at_cells, recv_nodes)
[(6, 1), (7, 6), (8, 8), (11, 6), (12, 7), (13, 8)]
"""
slope, receiver = calculate_steepest_descent_across_cell_faces(
grid, elevations, return_node=True)
(sink_cell, ) = numpy.where(slope >= 0.)
receiver[sink_cell] = grid.node_index_at_cells[sink_cell]
slope[sink_cell] = 0.
return receiver, slope
