Google Earth Engine – Extracting Raster Values for Points Using JavaScript API

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I want Extract pixel values by points from NDVI and convert it to a table in Google Earth Engine, but I don’t know what should I do.


var dataset = ee.ImageCollection('MODIS/061/MOD13Q1')
                  .filter(ee.Filter.date('2021-01-01', '2021-05-01'))
                  .mean();
var ndvi = dataset.select('NDVI');
var ndviVis = {
  min: 0.0,
  max: 8000.0,
  palette: [
    'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901',
    '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01',
    '012E01', '011D01', '011301'
  ],
};

var pts = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point([-118.6010, 37.0777]), {plot_id: 1}),
  ee.Feature(ee.Geometry.Point([-118.5896, 37.0778]), {plot_id: 2}),
  ee.Feature(ee.Geometry.Point([-118.5842, 37.0805]), {plot_id: 3}),
  ee.Feature(ee.Geometry.Point([-118.5994, 37.0936]), {plot_id: 4}),
  ee.Feature(ee.Geometry.Point([-118.5861, 37.0567]), {plot_id: 5})
]);

Map.addLayer(pts);

Map.centerObject(pts);
Map.addLayer(ndvi, ndviVis, 'NDVI');

Best Answer

You can use reduceRegions to apply a reducer over the pixels that intersect with your points. As you are working with a point layer, I suggest using first reducer.

// Applying first reducer
var results = ndvi.reduceRegions({
  collection: pts, 
  reducer: ee.Reducer.first(), 
  scale: 250, // Native resolution
});

// Print in console (the NDVI value will be named “first”).  
print(results);

//Export to Google Drive as csv file
Export.table.toDrive({
  collection: results,
  description:'RasterValues',
  fileFormat: 'csv'
});

Related Solutions

Google Earth Engine – Extracting Pixel Values by Points and Converting to Table

I have no access to your fusion table, so I made up one to make the answer.

First approach: 2D table

var yearly = ee.ImageCollection('JRC/GSW1_0/YearlyHistory');
// function to map over the FeatureCollection
var mapfunc = function(feat) {
  // get feature geometry
  var geom = feat.geometry()
  // function to iterate over the yearly ImageCollection
  // the initial object for the iteration is the feature
  var addProp = function(img, f) {
    // cast Feature
    var newf = ee.Feature(f)
    // get date as string
    var date = img.date().format()
    // extract the value (first) of 'waterClass' in the feature
    var value = img.reduceRegion(ee.Reducer.first(), geom, 30).get('waterClass')
    // if the value is not null, set the values as a property of the feature. The name of the property will be the date
    return ee.Feature(ee.Algorithms.If(value,
                                       newf.set(date, ee.String(value)),
                                       newf.set(date, ee.String('No data'))))
  }
  var newfeat = ee.Feature(yearly.iterate(addProp, feat))
  return newfeat
};

var newft = fg_points.map(mapfunc);

// Export
Export.table.toDrive(newft,
"export_Points",
"export_Points",
"export_Points");

Second approach: 1D table

var yearly = ee.ImageCollection('JRC/GSW1_0/YearlyHistory');
// function to map over the FeatureCollection
var mapfunc = function(feat) {
  // get feature id
  var id = ee.String(feat.id())
  // get feature geometry
  var geom = feat.geometry()
  // make an empty list to store the features
  var newfc = ee.List([])
  // function to iterate over the ImageCollection
  var addProp = function(img, fc) {
    // the initial value is the empty list
    fc = ee.List(fc)
    // get the date as string
    var date = img.date().format()
    // extract the value of 'waterClass'
    var value = img.reduceRegion(ee.Reducer.first(), geom, 30).get('waterClass')
    // If the value is null then store it as 'No data'
    var val = ee.String(ee.Algorithms.If(value, ee.String(value), ee.String('No data')))
    // make the name of the feature (feat_id-date)
    var featname = ee.String("feat_").cat(id).cat(ee.String("-")).cat(date)
    // make the Feature
    var newfeat = ee.Feature(geom, {name:featname,
                                    value:val})
    // add the value to the list
    return fc.add(newfeat)
  }
  var newfeat = ee.FeatureCollection(ee.List(yearly.iterate(addProp, newfc)))
  return newfeat
};

var newft = fg_points.map(mapfunc).flatten();

Export.table.toDrive(newft,
"export_Points",
"export_Points",
"export_Points");

If features in your FeatureCollection have a name property (or something that identifies each feat) you can change in the second approach:

var id = ee.String(feat.id())

for

var id = ee.String(feat.get('name'))

google-earth-engine – Extracting Min and Max Values of All Bands in Google Earth Engine

You can use reduceRegion() method on your image with reducer as ee.Reducer.minMax()

var minMax = dataset.reduceRegion({
    reducer: ee.Reducer.minMax(),
    geometry: roi,
    scale: 30,
    maxPixels: 1e10
})

print('Min & Max all bands: ', minMax)

Best Answer

Related Solutions

Google Earth Engine – Extracting Pixel Values by Points and Converting to Table

google-earth-engine – Extracting Min and Max Values of All Bands in Google Earth Engine

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