Centroid value extraction of Landsat image collection in Google Earth Engine

Question

I have an NDVI collection wich I have created from the combination of different collections Landsat5 and 7.

How can I exctract the NDVI values of the centroids of each pixel, of each image from my collection and store them in a csv file, with their coordinates?

Example code:

var lst5 = ee.ImageCollection('LANDSAT/LT05/C01/T1_SR')
    .filterDate('1984-10-01', '2011-10-01')
    .map(maskL57SR)
var lst7 = ee.ImageCollection('LANDSAT/LE07/C01/T1_SR')
    .filterDate('2011-10-01', '2013-04-07')
    .map(maskL57SR)
var all = ee.ImageCollection(lst5.merge(lst7));

var addNDVI = function(image) {
  var ndvi = image.normalizedDifference(['NIR', 'RED']).rename('NDVI');
  return image.addBands(ndvi);
};


all = all.map(addNDVI)

Answer 1

The main function to do this is ee.Image.reduceRegion.

// Define the point
var coords = [-71, -43]
var p = ee.Geometry.Point(coords);

Map.addLayer(p)

var lst5 = ee.ImageCollection('LANDSAT/LT05/C01/T1_SR')
    .filterDate('1984-10-01', '2011-10-01')
var lst7 = ee.ImageCollection('LANDSAT/LE07/C01/T1_SR')
    .filterDate('2011-10-01', '2013-04-07')
var all = ee.ImageCollection(lst5.merge(lst7));

var addNDVI = function(image) {
  var ndvi = image.normalizedDifference(['B4', 'B3']).rename('NDVI');
  return image.addBands(ndvi);
};

// remove 'limit' to compute the whole collection
all = all.map(addNDVI).filterBounds(p).limit(10)

// convert collection to list
var all_list = all.toList(all.size())

// map over collection
all_list = all_list.map(function(img){
  img = ee.Image(img)
  // get image values for point
  var values = img.reduceRegion({
    reducer: ee.Reducer.first(),
    geometry: p,
    scale: 30
  })
  // return as a Feature with no coordinates and values as properties
  return ee.Feature(null, values.set('img_id', img.id()))
})

// Create a FeatureCollection for exporting
var collection = ee.FeatureCollection(all_list)
print(collection)

// Export
Export.table.toDrive({
  collection: collection,
  folder: 'NAME OF FOLDER', 
  fileNamePrefix: 'NAME OF FILE', 
  fileFormat: 'CSV',
})

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