Getting Started with Google Earth Engine JavaScript API

To begin working with Earth Engine’s JavaScript API, you’ll need to access the Code Editor at code.earthengine.google.com. The interface includes:

• Code Editor panel for writing scripts
• Console for viewing outputs
• Map display area
• Inspector tool for examining map features
• Tasks panel for managing export operations

Basic JavaScript Concepts for Earth Engine

Variables and Assignment

In Earth Engine, you’ll work with server-side objects that are created and manipulated differently from regular JavaScript variables.

// Creating Earth Engine objects
var image = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20140318');
var geometry = ee.Geometry.Point([-122.082, 37.422]);
var number = ee.Number(42);
    

Object Methods and Chaining

Earth Engine objects have methods that can be chained together for complex operations:

var filteredCollection = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
  .filterBounds(geometry)
  .filterDate('2020-01-01', '2020-12-31')
  .sort('CLOUD_COVER')
  .limit(10);
    

Working with Images

Loading and Displaying Images

// Load a Landsat 8 image
var image = ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044034_20140318');

// Display the image
Map.addLayer(image, {bands: ['SR_B4', 'SR_B3', 'SR_B2'], min: 0, max: 3000}, 'Landsat Image');

// Center the map on the image
Map.centerObject(image, 8);
    

Image Processing Operations

// Calculate NDVI
var nir = image.select('SR_B5');
var red = image.select('SR_B4');
var ndvi = nir.subtract(red).divide(nir.add(red)).rename('NDVI');

// Add NDVI layer to map
Map.addLayer(ndvi, {min: -1, max: 1, palette: ['blue', 'white', 'green']}, 'NDVI');
    

Image Collections

Image collections are groups of images that share common properties:

// Load a Landsat 8 collection
var collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
  .filterDate('2020-06-01', '2020-09-01')
  .filterBounds(Map.getCenter())
  .select(['SR_B2', 'SR_B3', 'SR_B4', 'SR_B5']);

// Get collection information
print('Collection size:', collection.size());
print('First image:', collection.first());
    

Filters and Queries

Earth Engine provides various filtering options for collections:

var filtered = collection
  .filterBounds(geometry)              // Filter by location
  .filterDate('2020-01-01', '2020-12-31') // Filter by date
  .filterMetadata('CLOUD_COVER', 'less_than', 20) // Filter by metadata
  .sort('CLOUD_COVER')                 // Sort by property
  .limit(5);                           // Limit results
    

Geometries and Features

Creating Geometries

// Point geometry
var point = ee.Geometry.Point([-122.082, 37.422]);

// Polygon geometry
var polygon = ee.Geometry.Polygon([
  [[-122.085, 37.425],
   [-122.085, 37.420],
   [-122.075, 37.420],
   [-122.075, 37.425]]
]);

// Display geometries
Map.addLayer(point, {color: 'red'}, 'Point');
Map.addLayer(polygon, {color: 'blue'}, 'Polygon');
    

Reductions and Statistics

Reductions compute statistical summaries of images or collections:

// Calculate image statistics
var stats = ndvi.reduceRegion({
  reducer: ee.Reducer.mean(),
  geometry: polygon,
  scale: 30,
  maxPixels: 1e9
});

print('NDVI mean:', stats.get('NDVI'));
    

Mappings and Iterations

Apply functions to each image in a collection:

// Function to calculate NDVI for each image
var addNDVI = function(image) {
  var ndvi = image.normalizedDifference(['SR_B5', 'SR_B4']).rename('NDVI');
  return image.addBands(ndvi);
};

// Apply the function to each image in the collection
var collectionWithNDVI = collection.map(addNDVI);
    

Visualization and Export

Visualization Parameters

var visParams = {
  bands: ['SR_B4', 'SR_B3', 'SR_B2'],
  min: 0,
  max: 3000,
  gamma: 1.4
};

Map.addLayer(image, visParams, 'Landsat RGB');
    

Exporting Data

// Export image to Google Drive
Export.image.toDrive({
  image: ndvi,
  description: 'NDVI_export',
  folder: 'EarthEngine',
  fileNamePrefix: 'ndvi_map',
  region: polygon,
  scale: 30,
  maxPixels: 1e13
});