center_pivot_irrigation_detector.py

import ee 
from ee_plugin import Map 

# Center-pivot Irrigation Detector.
#
# Finds circles that are 500m in radius.
Map.setCenter(-106.06, 37.71, 12)

# A nice NDVI palette.
palette = [
  'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718',
  '74A901', '66A000', '529400', '3E8601', '207401', '056201',
  '004C00', '023B01', '012E01', '011D01', '011301']

# Just display the image with the palette.
image = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_034034_20170608')
ndvi = image.normalizedDifference(['B5','B4'])

Map.addLayer(ndvi, {'min': 0, 'max': 1, 'palette': palette}, 'Landsat NDVI')

# Find the difference between convolution with circles and squares.
# This difference, in theory, will be strongest at the center of
# circles in the image. This region is filled with circular farms
# with radii on the order of 500m.
farmSize = 500  # Radius of a farm, in meters.
circleKernel = ee.Kernel.circle(farmSize, 'meters')
squareKernel = ee.Kernel.square(farmSize, 'meters')
circles = ndvi.convolve(circleKernel)
squares = ndvi.convolve(squareKernel)
diff = circles.subtract(squares)

# Scale by 100 and find the best fitting pixel in each neighborhood.
diff = diff.abs().multiply(100).toByte()
max = diff.focal_max(**{'radius': farmSize * 1.8, 'units': 'meters'})
# If a pixel isn't the local max, set it to 0.
local = diff.where(diff.neq(max), 0)
thresh = local.gt(2)

# Here, we highlight the maximum differences as "Kernel Peaks"
# and draw them in red.
peaks = thresh.focal_max(**{'kernel': circleKernel})
Map.addLayer(peaks.updateMask(peaks), {'palette': 'FF3737'}, 'Kernel Peaks')

# Detect the edges of the features.  Discard the edges with lower intensity.
canny = ee.Algorithms.CannyEdgeDetector(ndvi, 0)
canny = canny.gt(0.3)

# Create a "ring" kernel from two circular kernels.
inner = ee.Kernel.circle(farmSize - 20, 'meters', False, -1)
outer = ee.Kernel.circle(farmSize + 20, 'meters', False, 1)
ring = outer.add(inner, True)

# Highlight the places where the feature edges best match the circle kernel.
centers = canny.convolve(ring).gt(0.5).focal_max({'kernel': circleKernel})
Map.addLayer(centers.updateMask(centers), {'palette': '4285FF'}, 'Ring centers')