有没有办法确保您在 Google 地球引擎的帮助下创建的马赛克是完整的？

Question

如标题中所述 - 我们正在尝试将马赛克中的数据用于项目，但数据只有在马赛克实际完成时才有意义。因此，如果我们选择的区域太大，卫星可能无法在一天的时间内飞越该地点，从而导致结果不完整。那么有没有办法只得到100%完整马赛克的结果呢？

这是我们使用的代码：

// Difference in days between start and finish
var diff = finish.difference(start, 'day');

// Make a list of all dates
var range = ee.List.sequence(0, diff.subtract(1)).map(function(day){return start.advance(day,'day')});

// Funtion for iteraton over the range of dates
var day_mosaics = function(date, newlist) {
  // Cast
  date = ee.Date(date);
  newlist = ee.List(newlist);

  // Filter collection between date and the next day
  var filtered = collection.filterDate(date, date.advance(1,'day'));

  // Make the mosaic and clip to aoi
  var clipped = ee.Image(filtered.mosaic().clip(aoi)).setMulti({'system:time_start': date});

  var footprint = ee.Feature(clipped.get('system:footprint'));

  // Add the mosaic to a list only if the collection has images
  return ee.List(ee.Algorithms.If(footprint.area().eq(aoi.area()), newlist.add(clipped), newlist));
};

// Iterate over the range to make a new list, and then cast the list to an imagecollection
var mosaic = ee.ImageCollection(ee.List(range.iterate(day_mosaics, ee.List([]))));
print(mosaic);

Answer 1

你已经有了查看足迹的想法，但它会更准确

使用 mask 像素而不是足迹几何图形，以防图像中有任何孔洞，并且
不是计算有效区域，而是找出是否有任何个无效区域。

var missingPixels = image
  .mask()  // Get the mask data as an image
  .reduce(ee.Reducer.min()) // Take the least coverage across all bands
  .expression('1 - b(0)')  // Invert the value
  .rename(['missing_pixels']);  // Give the result a better name

// Sum up missing pixel indications; if nonzero, some are missing. Pick a scale that is good enough for your purposes.
var noMissingPixels = missingPixels.reduceRegion({
  geometry: aoi,
  reducer: ee.Reducer.sum(),
  scale: 100
}).getNumber('missing_pixels').eq(0);
print(noMissingPixels);

https://code.earthengine.google.com/2dff320b7ab68e27e3acbd96efa23e4b

其他建议：iterate() 收集列表结果效率低下，应尽可能避免。当你想处理一个集合并丢弃一些元素时，你可以使用 map() 并将 dropNulls 参数设置为 true，并且 return null 用于任何元素你不想保留：

var day_mosaics = function(date) {
  ... regular code goes here, but no 'newlist' ...

  return ee.Algorithms.If(noMissingPixels, clipped, null);
};

var mosaic = ee.ImageCollection(range.map(day_mosaics, true));

这适用于非常大的集合，而构建列表可能运行内存不足。

有没有办法确保您在 Google 地球引擎的帮助下创建的马赛克是完整的？

Is there a way to be sure that the mosiaic you're creating with help of Googles Earth Engine is complete?

javascript

google-earth-engine