// CALCULO DE INDICES DE VEGETACION EN EARTH ENGINE
// http://www.gisandbeers.com/script-indices-de-vegetacion-google-earth-engine/


// Coleccion Sentinel 2 nivel 2
var ColeccionSentinel = ee.ImageCollection("COPERNICUS/S2_SR")
  .filterDate ('2020-04-01' ,'2020-05-30')
  //.filterBounds (geometry)
  .filterMetadata ('CLOUDY_PIXEL_PERCENTAGE', 'Less_Than', 20);
var Vegetacion = ee.Image(ColeccionSentinel.mean());

    
// NDVI (Normalized Difference Vegetation Index)
var NDVI = Vegetacion.expression ('float ((NIR - RED) / (NIR + RED))',{
    'NIR': Vegetacion.select ('B8'),  
    'RED': Vegetacion.select ('B4')});

// EVI (Enhanced Vegetation Index)
var EVI = Vegetacion.expression ('float (2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1)))', {
    'NIR': Vegetacion.select ('B8'),  
    'RED': Vegetacion.select ('B4'),
    'BLUE': Vegetacion.select ('B2')});

// GLI (Green Leaf Index)
var GLI = Vegetacion.expression ('float (((GREEN - RED) + (GREEN - BLUE)) / ((2 * GREEN) + RED + BLUE))', {
    'GREEN': Vegetacion.select ('B3'),  
    'RED': Vegetacion.select ('B4'),
    'BLUE': Vegetacion.select ('B2')});

// SAVI (Soil Adjusted Vegetation Index)
var SAVI = Vegetacion.expression ('float (((NIR - RED) / (NIR + RED + L))* (1+L))',{
    'L': 0.5, // Cobertura vegetacion 0-1
    'NIR': Vegetacion.select ('B8'),
    'RED': Vegetacion.select ('B4')});

// GCI (Green Chlorophyll Index)
var GCI = Vegetacion.expression ('float (((NIR) / (GREEN)) - 1)', {
    'NIR': Vegetacion.select ('B8'),  
    'GREEN': Vegetacion.select ('B3')});

// RGR (Red Green Ratio)
var RGR = Vegetacion.expression ('float ((RED) / (GREEN))', {
    'RED': Vegetacion.select ('B4'),  
    'GREEN': Vegetacion.select ('B3')});

// SIPI (Structure Insensitive Pigment Index)
var SIPI = Vegetacion.expression ('float ((NIR - BLUE) / (NIR - RED))',{
    'NIR': Vegetacion.select ('B8'),
    'BLUE': Vegetacion.select ('B2'), 
    'RED': Vegetacion.select ('B4')});

// ARVI (Atmospherically Resistant Vegetation Index)
var ARVI = Vegetacion.expression ('float ((NIR - (2 * RED) + BLUE) / (NIR + (2 * RED) + BLUE))',{
    'NIR': Vegetacion.select ('B8'),
    'BLUE': Vegetacion.select ('B2'), 
    'RED': Vegetacion.select ('B4')});

// NBRI (Normalized Burned Ratio Index)
var NBRI = Vegetacion.expression ('float (NIR - SWIR) / float (NIR + SWIR)', {
    'NIR': Vegetacion.select ('B8'),  
    'SWIR': Vegetacion.select ('B12')});

// Simbologia comun para los indices
var Simbologia = {max: 1, min: 0, // IMPORTANTE variar rangos en funcion del indice
    palette: ['#0000ff', 'DF923D', 'F1B555',
    'FCD163', '99B718', '74A901', '66A000', '529400', '3E8601', '207401',
    '056201', '004C00', '023B01', '012E01', '011D01', '011301']};
    
// Representacion de indices de vegetacion
Map.addLayer (NBRI, Simbologia, 'NBRI',0);
Map.addLayer (GCI, Simbologia, 'GCI',1);
Map.addLayer (RGR, Simbologia, 'RGR',0);
Map.addLayer (GLI, Simbologia, 'GLI',0);
Map.addLayer (SAVI, Simbologia, 'SAVI',0);
Map.addLayer (SIPI, Simbologia, 'SIPI',0);
Map.addLayer (EVI, Simbologia, 'EVI',0);
Map.addLayer (ARVI, Simbologia, 'ARVI',0);
Map.addLayer (NDVI, Simbologia, 'NDVI',0);
Map.addLayer (Vegetacion, {max: 4000.0, min: 0.0, gamma: 1.0, bands: ['B4','B3','B2']}, 'RGB color natural',0);

Map.setCenter (12.1, 45, 12);