Pixel extraction from many SENTINEL-3 products in SNAP

[daviguima]

Ok, sorry for flooding the thread but I have just found this answer from you:

Region of interest (ROI)

Hi Carlo, right-click in the view and select “Export Mask Pixels” The mask severs as a ROI. You can create masks by many different ways. You can load a shapefile, draw polygon or use Band Maths. Marco

And it is exactly what I need, now, how do I do it from the command line?