Image manipulation

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How do I get actual NDVI values?

If you want to get float values out of the service, you will have to use 32-bit float image type (as basic 8 and 16bit tiff files only support integeres).

You can define a Custom script along the following lines:

var ndvi = (B08-B04)/(B08+B04); 
  return [ndvi]; 

You can either save this in Configuration utility or you can pass it as EVALSCRIPT parameter. For the latter the example of the call is:

Are EO products being changed through time or is visualization fixed?

When user selects "EO Product template", she can see the Custom script behind each visualization/processing to make it as transparent as possible on what is happening with the data. We are changing these configurations through time, adding new ones and improving existing ones. For those, who want to ensure that processing of their layers is not changed any more, they can simply edit the original Custom script and gain full control over it.

What is the difference between “Atmospheric correction filter” and “L2A data source”

We have developed, only for Sentinel-2 data, run-time optimised statistical version of atmospheric correction. It is based on Sen2Cor technology, but uses anchor tiles and is not as accurate as the official Sen2Cor run on individual tiles.
With ESA starting to distribute L2A data form end of March 2017, you now have three options:

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