I am doing some validation of Sentinel-3 OLCI data (A/B). What I’ve noticed is in each Pixel Extraction output (I extract every parameter possible in a SEN3 folder), the headers are [‘ProdID’, ‘CoordID’, ‘Name’, ‘Latitude’, ‘Longitude’, ‘PixelX’, ‘PixelY’, etc.]. Name referring to the name of my input ‘extraction points’, and the respective Latitude and Longitude of those points. The Latitude and Longitude change with every satellite image file, so I should expect that these coordinates reflect actually, the pixel that is closest to the input coordinates. I also cross checked with original input coordinates and they are indeed not exactly the same, but very similar values.
Curiously, however, as SEN3 files also have coordinates in the geo_coordinates.nc file, these are extracted too, under lowercase ‘latitude’ and ‘longitude’. Although very similar, they are not the exact same values as from ‘Latitude’ and ‘Longitude’ (next to the name of the input ‘extraction points’ so to speak).
My question: Is there a source code somewhere I can find about the pixel extraction tool, or some documentation? And if the Latitude and Longitude parameters indeed reflect the pixel coordinates of the pixel closest to the input coordinates, why is it then different from the extracted pixel coordinates of the geo_coordinates.nc file? Should it not be the same? If not, where is the difference coming from and why?