Regarding the issue of data projection coordinate system and spatial resolution in Google Earth Engine #1969

AomineKai · 2024-04-15T10:44:26Z

AomineKai
Apr 15, 2024

Dear Professor Wu, hello!

"Here is a piece of code I wrote for extracting the annual maximum NDVI value, and I'd like to ask you a few questions. For example, when using the .updateMask() function, if the spatial resolution of other bands in Landsat is inconsistent, not all are 30 meters, and differs from the 30-meter spatial resolution of the 'NDVI' band, will GEE automatically adjust the spatial resolution of other Landsat bands to match the spatial resolution of the 'NDVI' band?

When performing some data processing, if the spatial resolutions of different bands in an image are inconsistent, will GEE handle it automatically? If it does, will GEE match high spatial resolution to low spatial resolution, or vice versa? Does it use nearest-neighbor interpolation? Do we need to consider the issue of projection coordinate system? If the spatial resolutions of different bands in an image are inconsistent, do we need to resample the data to the same resolution before processing it?"

// 导入矢量边界和样本点位
var region = boundary;
var samplePoints = samplePoints;

// 定义时间范围
var startDate = '2013-01-01';
var endDate = '2013-12-31';

// 加载并计算 Landsat 8 SR 影像中值数据
var landsat = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
.filterBounds(region)
.filterDate(startDate, endDate)
.median();

// 获取 Landsat 8 SR 影像数据集
var landsat8 = ee.ImageCollection('LANDSAT/LC08/C02/T1_L2')
.filterBounds(region)
.filterDate(startDate, endDate);

// 定义一个函数计算 NDVI
function addNDVI(image) {
var ndvi = image.normalizedDifference(['SR_B5', 'SR_B4']).rename('NDVI');
return image.addBands(ndvi);
}

// 对影像集中的每个影像应用 NDVI 函数
var landsat8WithNDVI = landsat8.map(addNDVI);

// 获取研究范围内所有 Landsat 8 影像对应像元的年度最大 NDVI 值
var maxNDVI = landsat8WithNDVI
.map(function(image) {
return image.updateMask(image.select('NDVI').gt(0)); // 过滤掉无效值
})
.reduce(ee.Reducer.max())
.clip(region);