Check on `pix_all` value to know if pixels are assigned to any of the sub-domains.

!#################################################################

!

! CSO Tutorial for observation operator code.

! Application on S5p data.

!

! CHANGES

!

!   2023-08, Arjo Segers

!     Check on `pix_all` value to know if pixels are assigned 

!     to any of the sub-domains.

!

!### macro's #####################################################

!

#define TRACEBACK write (logfu,'("in ",a," (",a,", line",i5,")")') rname, __FILE__, __LINE__

  character(len=64), allocatable    ::  uvarunits(:)  ! (nuvar)

  ! pixel counter and index:

  integer                           ::  npix

  integer                           ::  npix, npix_all

  integer                           ::  ipix 

  ! pixel footprints:

  real, pointer                     ::  lons(:), lats(:)         ! (npix)

      ! obtain info on track:

      !  - number of local pixels

      call sdata%Get( status, npix=npix )

      !  - total number of local pixels over all sub-domains

      call sdata%Get( status, npix=npix, npix_all=npix_all )

      IF_NOT_OK_RETURN(status=1)

      ! any pixels at all?

      if ( npix_all > 0 ) then

        ! initialize simulation state;

        ! optional arguments:

        !   description='long name'    : used for output attributes

        call sstate%EndDef( status )

        IF_NOT_OK_RETURN(status=1)

      ! any pixels?

        ! any local pixels?

        if ( npix > 0 ) then

          ! pointers to (*,pixel) arrays:

        call sstate%Done( sdata, status )

        IF_NOT_OK_RETURN(status=1)

      end if ! npix_all > 0

      ! done with data:

      call sdata%Done( status )

      IF_NOT_OK_RETURN(status=1)