[gdal-dev] MOD021KM subdatasets listing identical bands

[Nikos Alexandris]

According to `gdalinfo`, MOD021KM (and MYD021KM for the matter), list
identical bands under two different subdatasets (SDSes).

For example, SDS 3 (see `gdalinfo`'s report on it
https://gitlab.com/thermopolis/public/code/-/snippets/2021406)
and SDS 24 (see `gdalinfo`'s report on it
https://gitlab.com/thermopolis/public/code/-/snippets/2021407),
both contain essentially the same data/bands.

The obvious differences between the two SDSes are the descriptive name
(SDS 3 contains the characteristic, for this product, word 'SWATH') and
the set of ground control points (GCP) (SDS 24 does not list any GCPs
along).

I've search in every related official document I can find on-line about
MOD021KM products. I can't trace anything related to my question so far

(see for example:

- https://ladsweb.modaps.eosdis.nasa.gov/filespec/MODIS/61/MOD021KM
- https://mcst.gsfc.nasa.gov/sites/default/files/file_attachments/M1054E_PUG_2017_0901_V6.2.2_Terra_V6.2.1_Aqua.pdf
- https://mcst.gsfc.nasa.gov/sites/default/files/file_attachments/MODIS_L1B_ATBD_ver8_finalupload.pdf
  (although not the document that would expectedly contain details about
  the subdatasets in MOD02 products)
).

Panoply (https://www.giss.nasa.gov/tools/panoply/), however, contains
only once the set of Emissive bands at 1KM, and the same for the rest of
data (see https://i.imgur.com/llGYVfo.png).

What is the difference between the two SDSes?

Kind regards, Nikos