// บทเรียน Landsat data hand on 
// Code provided by Dr.Sitthisak Moukomla 

var Thailand = ee.FeatureCollection('USDOS/LSIB_SIMPLE/2017').filter(ee.Filter.eq('country_na', 'Thailand'));
             // Map.addLayer(Thailand);
var collection = ee.ImageCollection('LANDSAT/LC09/C02/T1_L2')
  .filterDate('2023-12-01','2024-02-15')
  .filterBounds(Thailand)
  .sort('CLOUD_COVER')
var c = collection.median();

// Applies scaling factors.
function applyScaleFactors(image) {
  var opticalBands = image.select('SR_B.').multiply(0.0000275).add(-0.2);
  var thermalBands = image.select('ST_*.*').multiply(0.00341802).add(149.0);
  return image.addBands(opticalBands, null, true)
              .addBands(thermalBands, null, true);
}

var dataset = applyScaleFactors(c);
var visualization = {
  bands: ['SR_B4', 'SR_B3', 'SR_B2'],
  min: 0.0,
  max: 0.25,
};
var image = dataset.select(['SR_B2', 'SR_B3', 'SR_B4', 'SR_B5'], ['blue', 'green', 'red', 'nir']);
// Extract VI band
var NDVI = image.normalizedDifference(['nir', 'red']);
var EVI = image.expression(
      "2.5 * ((nir - red) / (nir + 6 * red - 7.5 * blue + 1))", 
      {
      'nir' : image.select('nir'),
      'red' : image.select('red'),
      'blue': image.select('blue'),
      });

// Create palettes for display 
var pal = [
    '040274', '040281', '0502a3', '0502b8', '0502ce', '0502e6',
    '0602ff', '235cb1', '307ef3', '269db1', '30c8e2', '32d3ef',
    '3be285', '3ff38f', '86e26f', '3ae237', 'b5e22e', 'd6e21f',
    'fff705', 'ffd611', 'ffb613', 'ff8b13', 'ff6e08', 'ff500d',
    'ff0000', 'de0101', 'c21301', 'a71001', '911003'];
    
Map.addLayer(dataset.clip(Thailand), visualization, 'True Color (432)');
Map.addLayer(EVI.clip(Thailand), {min:0, max:1, palette: pal}, 'EVI');
Map.addLayer(NDVI.clip(Thailand), {min:0, max:1, palette: pal}, 'NDVI');
Map.centerObject(Thailand, 6);