Export the values in featurecollection using Google Earth Engine

Question

I want to export the values of NDVI and NDBI for the feature collection.

var data= L8TOA1.filterDate('2019-02-01', '2019-03-28') 
              .filter(ee.Filter.equals('WRS_PATH', 146))
              .filter(ee.Filter.eq('WRS_ROW', 40))
              .sort('CLOUD_COVER').first();
print(data);
//Get cloud cover information
var cloud= data.get('CLOUD_COVER');
print('cloud_cover is',cloud);
//Cip with boundary
var Study_region = data.clipToCollection(aoi);
// Define the visualization parameters.
var colour = {bands: ['B5', 'B4', 'B3'],min: 0,max: 0.5,gamma: 1.4,}
// Add layer to the map
Map.addLayer(Study_region,colour,'FCC');
Map.centerObject(aoi, 9);

//Indice
var NDBI = ee.Image (Study_region.normalizedDifference(['B6', 'B5']).rename('NDBI'));
var NDVI = ee.Image (Study_region.normalizedDifference(['B5', 'B4']).rename('NDVI'));
var SI= NDBI.addBands(NDVI)
print("Stacked_Image",SI);
var viz = [
'#FFFFFF','#808080','#000000','#FF0000', '#800000', '#FFFF00', '#008000', '#00FFFF', '#0000FF', '#FF00FF', '#800080'];
Map.addLayer(NDBI, {min: -1, max: 1, palette: viz},'NDBI');
// Get the Indices values to the point
var VTP = ee.FeatureCollection(SI.select(['NDBI','NDVI'])
  .reduceRegion({
  reducer: ee.Reducer.mean(),
  geometry: Urban.geometry(),
  scale: 30
}));
var Urban = Urban.set(VTP) ;
print('a',Urban);
print("Indices values to the point",VTP);
Export.table.toDrive({
collection: Urban,
description :"Indcies",
folder:"GEE",
fileNamePrefix: "Indcies",
fileFormat:"CSV",
selectors:['NDBI','NDVI']
});

When I exported the data, the value of NDBI and NDVI are not exported. Only the names were there exported. 

Answer 1

You're requesting export of a table. and columns like a database or spreadsheet. In Earth Engine, the “rows” of a table are features, and the “columns” are property names. Each cell contains the value of a property of the row feature.

You computed one value (using reduceRegion) and then put those results as properties of the feature collection, not any of its features using

var Urban = Urban.set(VTP) ;

The properties of the collection are not used in CSV export.

What to do instead depends on what you want.

• If you want to export just the two values, then you need to create a single feature for them, and put it into a collection, just so you have enough structure for the export to work:

  Export.table.toDrive({
      collection: ee.FeatureCollection([ee.Feature(null, VTP)]),
      ...
  });
  

• If you want to get the normalized difference values separately for each feature in Urban, then you should use reduceRegions({collection: Urban, ...}) instead of reduceRegion({geometry: Urban.geometry(), ...}). That will return a FeatureCollection with properties added to each feature, which you can then export.