GEE学习part5—图表函数与图表数据下载

代码：

//方法三：GEE将计算公式封装为一个方法可以直接调用
function NDVI_V3(img) {
 var ndvi = img.normalizedDifference(["B8","B4"]);
 return ndvi;
}


//sentinel2 and roi
var s2_col = ee.ImageCollection("COPERNICUS/S2");
var roi = ee.Geometry.Point([117.0703125,38.09133660751176]);
var img = ee.Image(s2_col.filterBounds(roi)
                       .filterDate("2018-05-01", "2018-09-24")
                       .first());
// var ndvi1 = NDVI_V1(img);
// var ndvi2 = NDVI_V2(img);
var ndvi3 = NDVI_V3(img);
var visParam = {
 min: -0.2,
 max: 0.8,
 palette: 'FFFFFF, CE7E45, DF923D, F1B555, FCD163, 99B718, 74A901, 66A000, 529400,' +
   '3E8601, 207401, 056201, 004C00, 023B01, 012E01, 011D01, 011301'
};
Map.addLayer(img, {bands:["B8", "B4", "B3"], max:3048}, "raw_img");
// Map.addLayer(ndvi1, visParam, "ndvi_1");
// Map.addLayer(ndvi2, visParam, "ndvi_2");
Map.addLayer(ndvi3, visParam, "ndvi_3");
Map.centerObject(roi, 9);

//show charts
var ndvi_list = s2_col.filterDate("2018-05-01", "2018-09-24")
   .map(function(image) {
   var ndvi = image.normalizedDifference(['B8', 'B4']).rename('NDVI');
   return image.addBands(ndvi);
});

//展示每一张影像NDVI值 
var chart1 = ui.Chart.image.series({
 //影像集合
 imageCollection: ndvi_list.select('NDVI'),
 //关心区域
 region: roi,
 //关心区域计算方式，这里采用的是均值。也就是比如roi是一个矩形，
 //那么在图表中这个点的值就是矩形内所有像素值求平均。
 reducer: ee.Reducer.mean(),
 //分辨率
 scale: 30
}).setOptions({title: 'NDVI IMAGE SERIES'});
print(chart1);

//展示每一天所关心区域的NDVI值
var chart2 = ui.Chart.image.doySeries({
 imageCollection: ndvi_list.select('NDVI'),
 region:roi,
 regionReducer: ee.Reducer.mean(),
 scale:30
}).setOptions({title: "ROI NDVI EACH DAY SERIES"})
print(chart2)