原文：quality mosaic
实践：
关键函数：greenest = withNDVI.qualityMosaic(‘NDVI’)

import ee
import geemap
geemap.set_proxy(10809)

Map =geemap.Map()
Map

Define a region of interest(ROI)

coun = "D:\learnpy\shp\countries.shp"
countries = geemap.shp_to_ee(coun)
Map.addLayer(countries, {} ,'countries')

roi = countries.filter(ee.Filter.eq('NAME','China'))
Map.addLayer(roi, {}, 'China')

Filter Collection

start_date = '2019-01-01'
end_date = '2019-12-31'l8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA') \.filterBounds(roi) \.filterDate(start_date, end_date)

print(l8.size().getInfo())
# 10374

Create a median compoiste

median = l8.median()visParams = {'bands': ['B4', 'B3', 'B2'],'min': 0,'max': 0.4,
}Map.addLayer(median, visParams, 'Median')

Define functions to add time bands

def addNDVI(image):ndvi = image.normalizedDifference(['B5', 'B4']).rename('NDVI')return image.addBands(ndvi)def addDate(image):img_date = ee.Date(image.date())img_date = ee.Number.parse(img_date.format('YYYYMMdd'))return image.addBands(ee.Image(img_date).rename('date').toInt())def addMonth(image):img_date = ee.Date(image.date())img_mon = ee.Number.parse(img_date.format('M'))return image.addBands(ee.Image(img_mon).rename('month').toInt())def addDOY(image):img_date = ee.Date(image.date())img_doy = ee.Number.parse(img_date.format('D'))return image.addBands(ee.Image(img_doy).rename('doy').toInt())

Map over an ImageCollection

withNDVI = l8.map(addNDVI).map(addDate).map(addMonth).map(addDOY)

Create a quality mosaic

greenest = withNDVI.qualityMosaic('NDVI')
greenest.bandNames().getInfo()
# ['B1',  'B2','B3','B4','B5','B6','B7','B8','B9','B10','B11', 'BQA', 'NDVI', 'date', 'month', 'doy']

Display the max value band

ndvi = greenest.select('NDVI')
palette = ['#d73027', '#f46d43', '#fdae61', '#fee08b', '#d9ef8b', '#a6d96a', '#66bd63', '#1a9850']
Map.addLayer(ndvi, {'palette': palette}, 'NDVI')

一年中最绿的月份

Map.addLayer(greenest.select('month'), {'palette': ['red', 'blue'], 'min': 1, 'max': 12}, 'Greenest month')

一年中最绿的天

Map.addLayer(greenest.select('doy'), {'palette': ['brown', 'green'], 'min': 1, 'max': 365}, 'Greenest doy')