Creating the hillshade

We can run this data through the same hillshade algorithm used in the Creating a shaded relief section, in Chapter 7, Python and Elevation Data:

# Hillshade the elevation image
log.info("Hillshading elevation data")
im = Image.open(elv_img + ".jpg").convert("L")
dem = np.asarray(im)

# Set up structure for a 3x3 window to
# process the slope throughout the grid
window = []
# x, y resolutions
xres = (maxx-minx)/w
yres = (maxy-miny)/h

# Create the windows
for row in range(3):
    for col in range(3):
        window.append(dem[row:(row + dem.shape[0]-2),
                      col:(col + dem.shape[1]-2)])

# Process each cell
x = ((z * window[0] + z * window[3] + z * window[3] + z * window[6]) -
     (z * window[2] + z * window[5] + z * window[5] + z * window[8])) \
     / (8.0 * xres * scale)

y = ((z * window[6] + z * window[7] + z * window[7] + z * window[8]) -
     (z * window[0] + z * window[1] + z * window[1] + z * window[2])) \
  ...