class AlgebraView(RasterView):
"""
A view to calculate map algebra on raster layers.
"""
def __init__(self, *args, **kwargs):
super(AlgebraView, self).__init__(*args, **kwargs)
self.parser = RasterAlgebraParser()
def get(self, request, masked=False, *args, **kwargs):
# Get layer ids
ids = request.GET.get('layers').split(',')
# Parse layer ids into dictionary with variable names
ids = {idx.split('=')[0]: idx.split('=')[1] for idx in ids}
# Get raster data as 1D arrays and store in dict that can be used
# for formula evaluation.
data = {}
for name, layerid in ids.items():
tile = self.get_tile(layerid)
if tile:
data[name] = tile
else:
# Create empty image if any layer misses the required tile
img = Image.new("RGBA", (WEB_MERCATOR_TILESIZE, WEB_MERCATOR_TILESIZE), (0, 0, 0, 0))
return self.write_img_to_response(img, {})
# Get formula from request
formula = request.GET.get('formula')
# Evaluate raster algebra expression, return 404 if not successfull
try:
# Evaluate raster algebra expression
result = self.parser.evaluate_raster_algebra(data, formula)
except:
raise Http404('Failed to evaluate raster algebra.')
# Get array from algebra result
result = result.bands[0].data()
# Render tile
colormap = self.get_colormap()
if colormap:
# Render tile using the legend data
img, stats = band_data_to_image(result, colormap)
else:
# Scale to grayscale rgb (can be colorscheme later on)
result = result.astype('float').ravel()
result = 255 * (result - numpy.min(result)) / (numpy.max(result) - numpy.min(result))
# Create rgba matrix from grayscale array
result = numpy.array((result, result, result, numpy.repeat(255, len(result)))).T
rgba = result.reshape(WEB_MERCATOR_TILESIZE, WEB_MERCATOR_TILESIZE, 4).astype('uint8')
# Create image from array
img = Image.fromarray(rgba)
stats = {}
# Return rendered image
return self.write_img_to_response(img, stats)
def __init__(self, *args, **kwargs):
super(AlgebraView, self).__init__(*args, **kwargs)
self.parser = RasterAlgebraParser()
def test_algebra_parser(self):
parser = RasterAlgebraParser()
result = parser.evaluate_raster_algebra(self.data, "x*(x>11) + 2*y + 3*z*(z==30)", check_aligned=True)
self.assertEqual(result.bands[0].data().ravel().tolist(), [92, 2, 14, 15])
