计算山体阴影

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from osgeo import gdal
from numpy import gradient
from numpy import pi
from numpy import arctan
from numpy import arctan2
from numpy import sin
from numpy import cos
from numpy import sqrt
import matplotlib.pyplot as plt
import subprocess

def hillshade(array, azimuth, angle_altitude):
    """
    :param array: input USGS ASCII DEM / CDED .dem
    :param azimuth: sun position
    :param angle_altitude: sun angle
    :return: numpy array
    """
    #计算梯度
     x, y = gradient(array)
    #计算坡度
     slope = pi/2. - arctan(sqrt(x*x + y*y))
    #计算坡向
     aspect = arctan2(-x, y)
    #计算方位角
     azimuthrad = azimuth * pi / 180.
    altituderad = angle_altitude * pi / 180.

    shaded = sin(altituderad) * sin(slope)     + cos(altituderad) * cos(slope)     * cos(azimuthrad - aspect)
    # return 255*(shaded + 1)/2
    return aspect

ds = gdal.Open(‘../geodata/092j02_0200_demw.dem‘)
arr = ds.ReadAsArray()

hs_array = hillshade(arr, 90, 45)
plt.imshow(hs_array,cmap=‘Greys‘)
plt.savefig(‘../geodata/hillshade_whistler.png‘)
plt.show()

# gdal command line tool called gdaldem
# link  http://www.gdal.org/gdaldem.html
# usage:
# gdaldem hillshade input_dem output_hillshade
# [-z ZFactor (default=1)] [-s scale* (default=1)]"
# [-az Azimuth (default=315)] [-alt Altitude (default=45)]
# [-alg ZevenbergenThorne] [-combined]
# [-compute_edges] [-b Band (default=1)] [-of format] [-co "NAME=VALUE"]* [-q]

create_hillshade = ‘‘‘gdaldem hillshade -az 315 -alt 45 ../geodata/092j02_0200_demw.dem ../geodata/hillshade.tif‘‘‘

#通过标准库中的subprocess包来fork一个子进程，并运行一个外部的程序
subprocess.call(create_hillshade)