错误：
Error generating chart: The image collection is empty.
No features contain non-null values of "system:time_start".
The image collection is empty.
原始代码：
var geometry = /* color: #d63000 */ee.Geometry.Polygon( [[[-81.14573791618602, 25.335453210591712], [-80.90953186149852, 25.32924702619973], [-81.03312805290477, 25.5190118912932], [-81.1992962657954, 25.50537864099872]]]), Mang = ee.FeatureCollection("users/selenachav5/mangrove_vector"); var WSC1050 = /* color: #98ff00 */ee.Geometry.Point([-81.11963534, 25.42344856]); var mask = Mang var mangroveImg = ee.Image(0).paint(mask, 1); Map.addLayer(mangroveImg, {min:0, max:1}, 'mangroveImg') function maskNonMangrove(i){ return i.updateMask(mangroveImg).copyProperties(i); } var col = ee.ImageCollection('MODIS/061/MOD13Q1') .map(function(im) {return im.select(['NDVI']).multiply(0.0001)}) .filter(ee.Filter.date('2013-01-01', '2023-05-01')) .map(maskNonMangrove) ; var ndvi = col.select('NDVI'); var ndviVis = { min: 0.0, max: 8000.0, palette: [ 'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901', '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01', '012E01', '011D01', '011301' ], }; Map.setCenter(6.746, 46.529, 2); Map.addLayer(ndvi, ndviVis, 'NDVI'); var ndviChart = ui.Chart.image.series(ndvi, WSC1050, ee.Reducer.mean(), 250); ndviChart.setOptions({ title: 'MODIS NDVI', vAxis: {title: 'NDVI', maxValue: 9000}, hAxis: {title: 'date', format: 'MM-yy', gridlines: {count: 7}}, }); print(ndviChart)
解析：
出现这个的主要原因是，我们在对影像集合进行映射计算的出现了掩盖掉时间属性的东西，所以我们需要在进行映射函数之后要进行属性的追加，也就是及逆行属性的copy，从而保留这个时间属性，因为在默认状态下chart中是需要进行时间属性的来作为横轴进行加载的，所以这里我们必须要保留原有的影像时间信息。
关键代码：
.copyProperties(i,['system:time_start'])
图表函数：
ui.Chart.image.series(imageCollection, region, reducer, scale, xProperty)
Generates a Chart from an ImageCollection. Plots derived values of each band in a region across images. Usually a time series.
- X-axis: Image, labeled by xProperty value.
- Y-axis: Band value.
- Series: Band names.
Returns a chart.
Arguments:
imageCollection (ImageCollection):
An ImageCollection with data to be included in the chart.
region (Feature|FeatureCollection|Geometry):
The region to reduce.
reducer (Reducer, optional):
Reducer that generates the values for the y-axis. Must return a single value. Defaults to ee.Reducer.mean().
scale (Number, optional):
Scale to use with the reducer in meters.
xProperty (String, optional):
Property to be used as the label for each image on the x-axis. Defaults to 'system:time_start'.
Returns: ui.Chart
修改后的代码：
var WSC1050 = /* color: #98ff00 */ee.Geometry.Point([-81.11963534, 25.42344856]); var mask = Mang var mangroveImg = ee.Image(0).paint(mask, 1); Map.addLayer(mangroveImg, {min:0, max:1}, 'mangroveImg') function maskNonMangrove(i){ return i.updateMask(mangroveImg).copyProperties(i,['system:time_start']); } var col = ee.ImageCollection('MODIS/061/MOD13Q1') .map(function(i) {return i.select(['NDVI']).multiply(0.0001).copyProperties(i,['system:time_start'])}) .filter(ee.Filter.date('2013-01-01', '2023-05-01')) .map(maskNonMangrove) ; var ndvi = col.select('NDVI'); var ndviVis = { min: 0.0, max: 8000.0, palette: [ 'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901', '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01', '012E01', '011D01', '011301' ], }; Map.setCenter(6.746, 46.529, 2); Map.addLayer(ndvi, ndviVis, 'NDVI'); var ndviChart = ui.Chart.image.series(ndvi, WSC1050, ee.Reducer.mean(), 250); ndviChart.setOptions({ title: 'MODIS NDVI', vAxis: {title: 'NDVI', maxValue: 1}, hAxis: {title: 'date', format: 'MM-yy', gridlines: {count: 7}}, }); print(ndviChart)
