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hillshade.py
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hillshade.py
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import math
from functools import partial
from typing import Optional
import dask.array as da
import numpy as np
import xarray as xr
from numba import cuda
from .gpu_rtx import has_rtx
from .utils import calc_cuda_dims, has_cuda_and_cupy, is_cupy_array, is_cupy_backed
def _run_numpy(data, azimuth=225, angle_altitude=25):
data = data.astype(np.float32)
azimuth = 360.0 - azimuth
x, y = np.gradient(data)
slope = np.pi/2. - np.arctan(np.sqrt(x*x + y*y))
aspect = np.arctan2(-x, y)
azimuthrad = azimuth*np.pi/180.
altituderad = angle_altitude*np.pi/180.
shaded = np.sin(altituderad) * np.sin(slope) + \
np.cos(altituderad) * np.cos(slope) * \
np.cos((azimuthrad - np.pi/2.) - aspect)
result = (shaded + 1) / 2
result[(0, -1), :] = np.nan
result[:, (0, -1)] = np.nan
return result
def _run_dask_numpy(data, azimuth, angle_altitude):
data = data.astype(np.float32)
_func = partial(_run_numpy, azimuth=azimuth, angle_altitude=angle_altitude)
out = data.map_overlap(_func,
depth=(1, 1),
boundary=np.nan,
meta=np.array(()))
return out
@cuda.jit
def _gpu_calc_numba(
data,
output,
sin_altituderad,
cos_altituderad,
azimuthrad
):
i, j = cuda.grid(2)
if i > 0 and i < data.shape[0]-1 and j > 0 and j < data.shape[1] - 1:
x = (data[i+1, j]-data[i-1, j])/2
y = (data[i, j+1]-data[i, j-1])/2
len = math.sqrt(x*x + y*y)
slope = 1.57079632679 - math.atan(len)
aspect = (azimuthrad - 1.57079632679) - math.atan2(-x, y)
sin_slope = math.sin(slope)
sin_part = sin_altituderad * sin_slope
cos_aspect = math.cos(aspect)
cos_slope = math.cos(slope)
cos_part = cos_altituderad * cos_slope * cos_aspect
res = sin_part + cos_part
output[i, j] = (res + 1) * 0.5
def _run_cupy(d_data, azimuth, angle_altitude):
# Precompute constant values shared between all threads
altituderad = angle_altitude * np.pi / 180.
sin_altituderad = np.sin(altituderad)
cos_altituderad = np.cos(altituderad)
azimuthrad = (360.0 - azimuth) * np.pi / 180.
# Allocate output buffer and launch kernel with appropriate dimensions
import cupy
d_data = d_data.astype(cupy.float32)
output = cupy.empty(d_data.shape, np.float32)
griddim, blockdim = calc_cuda_dims(d_data.shape)
_gpu_calc_numba[griddim, blockdim](
d_data, output, sin_altituderad, cos_altituderad, azimuthrad
)
# Fill borders with nans.
output[0, :] = cupy.nan
output[-1, :] = cupy.nan
output[:, 0] = cupy.nan
output[:, -1] = cupy.nan
return output
def hillshade(agg: xr.DataArray,
azimuth: int = 225,
angle_altitude: int = 25,
name: Optional[str] = 'hillshade',
shadows: bool = False) -> xr.DataArray:
"""
Calculates, for all cells in the array, an illumination value of
each cell based on illumination from a specific azimuth and
altitude.
Parameters
----------
agg : xarray.DataArray
2D NumPy, CuPy, NumPy-backed Dask, or Cupy-backed Dask array
of elevation values.
angle_altitude : int, default=25
Altitude angle of the sun specified in degrees.
azimuth : int, default=225
The angle between the north vector and the perpendicular
projection of the light source down onto the horizon
specified in degrees.
name : str, default='hillshade'
Name of output DataArray.
shadows : bool, default=False
Whether to calculate shadows or not. Shadows are available
only for Cupy-backed Dask arrays and only if rtxpy is
installed and appropriate graphics hardware is available.
Returns
-------
hillshade_agg : xarray.DataArray, of same type as `agg`
2D aggregate array of illumination values.
References
----------
- GeoExamples: http://geoexamples.blogspot.com/2014/03/shaded-relief-images-using-gdal-python.html # noqa
Examples
--------
.. sourcecode:: python
>>> import numpy as np
>>> import xarray as xr
>>> from xrspatial import hillshade
>>> data = np.array([
... [0., 0., 0., 0., 0.],
... [0., 1., 0., 2., 0.],
... [0., 0., 3., 0., 0.],
... [0., 0., 0., 0., 0.],
... [0., 0., 0., 0., 0.]])
>>> n, m = data.shape
>>> raster = xr.DataArray(data, dims=['y', 'x'], name='raster')
>>> raster['y'] = np.arange(n)[::-1]
>>> raster['x'] = np.arange(m)
>>> hillshade_agg = hillshade(raster)
>>> print(hillshade_agg)
<xarray.DataArray 'hillshade' (y: 5, x: 5)>
array([[ nan, nan, nan, nan, nan],
[ nan, 0.71130913, 0.44167341, 0.71130913, nan],
[ nan, 0.95550163, 0.71130913, 0.52478473, nan],
[ nan, 0.71130913, 0.88382559, 0.71130913, nan],
[ nan, nan, nan, nan, nan]])
Coordinates:
* y (y) int32 4 3 2 1 0
* x (x) int32 0 1 2 3 4
"""
if shadows and not has_rtx():
raise RuntimeError(
"Can only calculate shadows if cupy and rtxpy are available")
# numpy case
if isinstance(agg.data, np.ndarray):
out = _run_numpy(agg.data, azimuth, angle_altitude)
# cupy/numba case
elif has_cuda_and_cupy() and is_cupy_array(agg.data):
if shadows and has_rtx():
from .gpu_rtx.hillshade import hillshade_rtx
out = hillshade_rtx(agg, azimuth, angle_altitude, shadows=shadows)
else:
out = _run_cupy(agg.data, azimuth, angle_altitude)
# dask + cupy case
elif (has_cuda_and_cupy() and isinstance(agg.data, da.Array) and
is_cupy_backed(agg)):
raise NotImplementedError("Dask/CuPy hillshade not implemented")
# dask + numpy case
elif isinstance(agg.data, da.Array):
out = _run_dask_numpy(agg.data, azimuth, angle_altitude)
else:
raise TypeError('Unsupported Array Type: {}'.format(type(agg.data)))
return xr.DataArray(out,
name=name,
coords=agg.coords,
dims=agg.dims,
attrs=agg.attrs)