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I tried to export Sentinel 1A to Google Drive on Google Earth Engine. The function has a parameter name "scale" which determines pixel scale of the exported image. 

Export.image.toDrive({
    image:imgtype[type],
    description: id,
    folder: folder,
    fileNamePrefix: id,
    region: region,
    scale: scale,
    maxPixels: maxPixels})
}

From the docs, it is said that Sentinel 1A has three resolution: 10m, 25m and 40m. My questions are:

  1. If I set scale = one of three above scale, is the exported image original image or resampled image. And if it is resampled, then what resampling method is used?
  2. If scale = another number (i.e. 20, 50, ...) then how GEE produce those images to Google Drive?
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  • If you want to know how GEE works in the 'Server side' you better ask in groups.google.com/forum/#!forum/google-earth-engine-developers
    – Rodrigo E. Principe
    Commented Nov 16, 2017 at 14:47
  • Thank you very much. Unfortunately, I am not able to join the group, it is by invitation only. And the code above is from your library :))
    – mdc
    Commented Nov 17, 2017 at 4:08
  • I won't give you an answer because I don't have the knowledge about what happens in the 'Server side', but I believe that: 1) Image are re-sampled but the algorithm is executed in the server side, so I don't know which one it is, and 2) I guess so. Another thing, Export.image.toDrive is not my authority, it's just an EE function I use in my code =) I think some people that give answers in this forum belong to EE staff, like Tyler Erickson and Nicholas Clinton
    – Rodrigo E. Principe
    Commented Nov 17, 2017 at 12:16
  • Rodrigo - Asking questions about the server-side aspects of Earth Engine in GIS.stackexchange is fine.
    – Tyler Erickson
    Commented Nov 17, 2017 at 20:51
  • Hi @TylerErickson, you are right, what I meant was that the core processing of GEE is done in the server side, so the staff of GEE may know better what happens there, but you are right, it was in the documentation! my mistake. Regards
    – Rodrigo E. Principe
    Commented Nov 20, 2017 at 16:28

1 Answer 1

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  1. If you want to export the original image, set the crs, crsTransform and dimensions parameters to match the values of the original image. Setting the scale value may get you similar results, but scale is a less direct specification of the coordinate reference system (CRS).

  2. If a different CRS is specified (using the scale or crs and crsTransform parameters), Earth Engine selects the nearest scaled image from the asset's image pyramid, and resamples (using nearest neighbor by default) as necessary. See the Scale documentation page for more details.

For even more details, see the Projections, Resampling and Reducing Resolution and Exporting Data pages of the Earth Engine documentation.

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