[gdal-dev] MOD021KM subdatasets listing identical bands

[Nikos Alexandris]

* Nikos Alexandris <nik at nikosalexandris.net> [2020-10-02 12:32:31 +0200]:

>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?

I am forwarding NASA's reply on the matter:
"
    Following up to your yesterday's information, we discussed this
    entirely. We do not have access to gdal and would need more effort
    installing and familiarizing with it. Generally, there is only one
    dataset "EV_1KM_Emissive" in MOD021KM/MYD021KM data file, and it resides
    in "MODIS_SWATH_Type_L1B". To our best guess, gdal reads subdataset list
    at swatch layer, grid layer and SDSs. That is why there are duplicated
    subdatasets shown in the list, but they belong to SWATH layer and SDS,
    respectively.

    Regards,
    LAADS User Services


    Ticket Details
    ---------------------------------
    Ticket ID: 108294
    Department: LAADS DAAC
    Type: General
    Status: Waiting for User
    Priority: Low
"

I find it a bit confusing to have duplicate data reported by gdalinfo.
Cheers, Nikos