Develop an App to Calculate Mean NDVI at Any Point.

The Normalized Difference Vegetation Index (NDVI) is a simple graphical indicator that can be used to analyze remote sensing measurements, typically, but not necessarily, from a space platform, and assess whether the target being observed contains live green vegetation or not.

The NDVI is calculated from these individual measurements as follows:

NDVI= (NIR-Red) \ (NIR+Red)

In this tutorial we will learn to develop a simple app that displays Mean NDVI at any point we click. Learn how to create Earth Engine App, here:

``````// Filter a collection to a time of interest.
var l8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA')
.filterDate('2014-06-01', '2015-06-01');

var ndvi = l8.map(function(image) {
return image.select().addBands(image.normalizedDifference(['B5', 'B4']));
});

// Nice visualization parameters for a vegetation index.
var vis = {min: 0, max: 1, palette: [
'FFFFFF', 'CE7E45', 'FCD163', '66A000', '207401',
'056201', '004C00', '023B01', '012E01', '011301']};
Map.addLayer(ndvi, vis, 'NDVI');
Map.setCenter(20.049, -0.13, 8);

// Create an inspector panel with a horizontal layout.
var inspector = ui.Panel({
layout: ui.Panel.Layout.flow('horizontal')
});

// Add a label to the panel.
inspector.add(ui.Label('Click to get mean NDVI'));

// Add the panel to the default map.
Map.add(inspector);

// Set the default map's cursor to a "crosshair".
Map.style().set('cursor', 'crosshair');

// Register a callback on the map to be invoked when the map is clicked.
Map.onClick(function(coords) {
// Clear the panel and show a loading message.
inspector.clear();
inspector.style().set('shown', true);
inspector.add(ui.Label('Loading...', {color: 'gray'}));

// Compute the mean NDVI; a potentially long-running server operation.
var point = ee.Geometry.Point(coords.lon, coords.lat);
var temporalMean = ndvi.reduce(ee.Reducer.mean());
var sampledPoint = temporalMean.reduceRegion(ee.Reducer.mean(), point, 30);
var computedValue = sampledPoint.get('nd_mean');

// Request the value from the server and use the results in a function.
computedValue.evaluate(function(result) {
inspector.clear();

// Add a label with the results from the server.
inspector.add(ui.Label({
value: 'Mean NDVI: ' + result.toFixed(2),
style: {stretch: 'vertical'}
}));

// Add a button to hide the Panel.
inspector.add(ui.Button({
label: 'Close',
onClick: function() {
inspector.style().set('shown', false);
}
}));
});
});
``````