Vegetation analysis.js

// OBJECTIVE: Calculate variation of NDVI on a specific period

///////////////// CODE FOR CALCULATING NDVI ///////////////////////
var drawingTools = Map.drawingTools();
drawingTools.setShown(false);
Map.setCenter(13.58, 20.31, 3);


// Setup a while loop to clear all existing geometries that have been added as imports from drawing tools (from previously running the script). The design of the app is to handle charting a time series for a single geometry, so remove any that exist.
while (drawingTools.layers().length() > 0) {
  var layer = drawingTools.layers().get(0);
  drawingTools.layers().remove(layer);
}

var dummyGeometry =
    ui.Map.GeometryLayer({geometries: null, name: 'geometry', color: '23cba7'});

drawingTools.layers().add(dummyGeometry);

function clearGeometry() {
  var layers = drawingTools.layers();
  layers.get(0).geometries().remove(layers.get(0).geometries().get(0));
}

function drawRectangle() {
  clearGeometry();
  drawingTools.setShape('rectangle');
  drawingTools.draw();
}

function drawPolygon() {
  clearGeometry();
  drawingTools.setShape('polygon');
  drawingTools.draw();
}

var chartPanel = ui.Panel({
  style:
      {height: '235px', width: '600px', position: 'bottom-right', shown: false}
});

Map.add(chartPanel);

function chartNdviTimeSeries() {
  // Make the chart panel visible the first time a geometry is drawn.
  if (!chartPanel.style().get('shown')) {
    chartPanel.style().set('shown', true);
  }

  // Get the drawn geometry; it will define the reduction region.
  var aoi = drawingTools.layers().get(0).getEeObject();

  // Set the drawing mode back to null; turns drawing off.
  drawingTools.setShape(null);

  // Reduction scale is based on map scale to avoid memory/timeout errors.
  var mapScale = Map.getScale();
  var scale = mapScale > 5000 ? mapScale * 2 : 5000;

  // Chart NDVI time series for the selected area of interest.
  var chart = ui.Chart.image
                  .seriesByRegion({
                    imageCollection: ee.ImageCollection('MODIS/006/MOD13A2'),
                    regions: aoi,
                    reducer: ee.Reducer.mean(),
                    band: 'NDVI',
                    scale: scale,
                    xProperty: 'system:time_start'
                  })
                  .setOptions({
                    titlePostion: 'none',
                    legend: {position: 'none'},
                    hAxis: {title: 'Date'},
                    vAxis: {title: 'NDVI (x1e4)'},
                    series: {0: {color: '23cba7'}}
                  });

  // Replace the existing chart in the chart panel with the new chart.
  chartPanel.widgets().reset([chart]);
}

drawingTools.onDraw(ui.util.debounce(chartNdviTimeSeries, 500));
drawingTools.onEdit(ui.util.debounce(chartNdviTimeSeries, 500));

var symbol = {
  rectangle: '⬛',
  polygon: '🔺',
};

var controlPanel = ui.Panel({
  widgets: [
    ui.Label('1. Select a drawing mode.'),
    ui.Button({
      label: symbol.rectangle + ' Rectangle',
      onClick: drawRectangle,
      style: {stretch: 'horizontal'}
    }),
    ui.Button({
      label: symbol.polygon + ' Polygon',
      onClick: drawPolygon,
      style: {stretch: 'horizontal'}
    }),
    ui.Label('2. Draw a geometry.'),
    ui.Label('3. Wait for chart to render.'),
    ui.Label(
        '4. Repeat 1-3 or edit/move\ngeometry for a new chart.',
        {whiteSpace: 'pre'})
  ],
  style: {position: 'bottom-left'},
  layout: null,
});

Map.add(controlPanel);
Map.add(ui.Label('Automated vegetation estimations (NDVI)', {fontWeight: 'bold', fontSize: '24px'}))

var img2020 = ee.ImageCollection('MODIS/006/MOD13A2').filterDate('2021-01-01', '2021-02-01').select('NDVI');
var NDVIVis = {
    min: 0.0,
    max: 6000.0,
    opacity: 0.4,
    palette: ['24126c', 'd4ff50', '1fff4f'],
    };

Map.addLayer(img2020, NDVIVis, 'NDVI')


///////////////////////////////////////////////////////////////////