函数：

size()

Returns the number of elements in the collection.

返回集合中元素的数量。

Arguments:

this:collection (FeatureCollection):

The collection to count.

Returns: Integer

融合影像可以一个接一个进行融合

merge(collection2)

Merges two image collections into one. The result has all the images that were in either collection.将两个图片集合并为一个。其结果是所有的图像都在任何一个集合中。

Arguments:

this:collection1 (ImageCollection):

The first collection to merge.

collection2 (ImageCollection):

The second collection to merge.

Returns: ImageCollection