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How to reduce image collections in Earth Engine?
Instead of just taking the last pixel in the collection (when you add a collection to the map, Earth Engine implicitly calls mosaic () on it), you can reduce the ImageCollection ( Learn more about reducing image collections ). You were first introduced to reducers for getting statistics in an image region. That was a spatial reduction.
How does Earth Engine pick the most recent pixel?
Merely adding the collection to the map results in selecting the most recent pixel – the one from the latest image in the stack. This behavior may be altered, using Earth Engine reducers. For example, rather than take the most recent pixel from the stack, Earth Engine can be instructed to pick the median value in the stack.
Where does each pixel on a map come from?
Each pixel on the map is derived from a stack of pixels – one from each image in the collection being displayed. Merely adding the collection to the map results in selecting the most recent pixel – the one from the latest image in the stack. This behavior may be altered, using Earth Engine reducers.
How does masking work in Google Earth Engine?
Masking pixels in an image makes those pixels transparent and excludes them from analysis. Each pixel in each band of an image has a mask. Those with a mask value of 0 or below will be transparent. Those with a mask of any value above 0 will be rendered.
How to filter clouds in Google Earth Engine?
Watch out for ROIs that overlap a scene’s footprint, but do not contain any valid pixels. Also watch out for ROIs that are very large or span multiple WRS cells. // SimpleCloudScore, an example of computing a cloud-free composite with L8 // by selecting the least-cloudy pixel from the collection.
What’s the problem with mosaic in Earth Engine?
One of the problems with this composite is that it’s full of clouds. Instead of just taking the last pixel in the collection (when you add a collection to the map, Earth Engine implicitly calls mosaic () on it), you can reduce the ImageCollection ( Learn more about reducing image collections ).