Using Overloaded Operators to Compute the EVI (Sentinel-2)

Tutorial created by **David Montero Loaiza**: GitHub | Twitter

GitHub Repo: https://github.com/davemlz/eemont
PyPI link: https://pypi.org/project/eemont/
Conda-forge: https://anaconda.org/conda-forge/eemont
Documentation: https://eemont.readthedocs.io/
More tutorials: https://github.com/davemlz/eemont/tree/master/docs/tutorials

Let’s start!

If required, please uncomment:

[1]:

#!pip install eemont
#!pip install geemap

Import the required packages.

[2]:

import ee, eemont, datetime, geemap

Authenticate and Initialize Earth Engine and geemap.

[3]:

Map = geemap.Map()

Point of interest.

[4]:

point = ee.Geometry.Point([-76.0269,2.92846])

Get, filter, mask clouds and scale the image collection.

[5]:

S2 = (ee.ImageCollection('COPERNICUS/S2_SR')
      .filterBounds(point)
      .sort('CLOUDY_PIXEL_PERCENTAGE')
      .first()
      .maskClouds()
      .scaleAndOffset()
      .spectralIndices('EVI')) # Let's compute the EVI using the index() method for comparison

Let’s select the required bands for EVI:

[6]:

N = S2.select('B8')
R = S2.select('B4')
B = S2.select('B2')

Overloaded Operators

eemont has overloaded the binary operators, rich comparisons and unary operators in the following list for the ee.Image class:

(+, -, *, /, //, %, **, <<, >>, &, |, <, <=, ==, !=, >, >=, -, ~)

Therefore, you can now use them for image operations!

[7]:

EVI = 2.5 * (N - R) / (N + 6.0 * R - 7.5 * B + 1.0)

Visualization

Let’s define the EVI visualization parameters:

[8]:

visEVI = {
    'min':0,
    'max':1,
    'palette':[
        'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901', '66A000',
        '529400', '3E8601', '207401', '056201', '004C00', '023B01', '012E01', '011D01', '011301'
    ]
}

And also the RGB visualization parameters:

[9]:

visRGB = {
    'min':0,
    'max':0.3,
    'bands':['B4', 'B3', 'B2']
}

Use geemap to display results:

[10]:

Map.addLayer(S2,visRGB,'RGB')
Map.addLayer(EVI,visEVI,'EVI With Overloaded Operators')
Map.addLayer(S2.select('EVI'),visEVI,'EVI With index() Method')
Map.add_colorbar(visEVI['palette'], caption = 'EVI')
Map.centerObject(point,9)
Map

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