DEFINE HEADER

        [SIC\]DEFINE HEADER Var1 File1 Key1 [Var2 File2 Key2 [...]]
                    [/GLOBAL] [/TRIM [Rank]] [/LIKE OtherVar]

    Define  variables  associated to the HEADER of the GILDAS images located
    in the files specified by File1, File2, etc...  The keywords Key1, Key2,
    etc... must be either READ or WRITE.

    FileJ  can  be  * to define a virtual header. In this case, KeyJ must be
    IMAGE or UVDATA. VarJ must include the dimensions, or the  /LIKE  option
    should be present to derive them from an existing image.

    The following variables are defined:

       ! General section
       VAR%GENE       Integer        Length of section
       VAR%NDIM       Integer        Number of dimensions (ReadOnly)
       VAR%DIM        Integer[7]     Dimensions           (ReadOnly)
       VAR%CONVERT    Double[3,7]    Conversion formulae for the 7 axes:
                                     Reference pixel,
                                     Value at reference pixel,
                                     Increment

       ! Blanking section
       VAR%BLAN       Integer        Length of section
       VAR%BLANK      Real[2]        Blanking and tolerance

       ! Extrema section
       VAR%EXTREMA    Integer        Length of section
       VAR%MAX        Real           Maximum of data
       VAR%MIN        Real           Minimum of data
       VAR%MINLOC     Integer[7]     Position of min
       VAR%MAXLOC     Integer[7]     Position of max

       ! Units and coordinates system section
       VAR%DESC       Integer        Length of section
       VAR%UNIT       Char*12        Image unit
       VAR%UNIT1      Char*12        First axis type
       VAR%UNIT2      Char*12        Second axis type
       VAR%UNIT3      Char*12        Third axis type
       VAR%UNIT4      Char*12        Fourth axis type
       VAR%SYSTEM     Char*12        Coordinate system

       ! Position section
       VAR%POSI       Integer        Length of section
       VAR%SOURCE     Char*12        Source name
       VAR%RA         Double         Right Ascension
       VAR%DEC        Double         Declination
       VAR%LII        Double         Galactic longitude
       VAR%BII        Double         Galactic latitude
       VAR%EQUINOX    Real           Equinox of coordinates

       ! Projection section
       VAR%PROJ       Integer        Length of section
       VAR%PTYPE      Integer        Projection type (code)
       VAR%A0         Double         First coordinate of projection center
       VAR%D0         Double         Second coordinate of projection center
       VAR%ANGLE      Double         Position angle of projection
       VAR%X_AXIS     Integer        First projected axis
       VAR%Y_AXIS     Integer        Second projected axis

       ! Spectroscopy section
       VAR%SPEC       Integer        Length of section
       VAR%LINE       Char*12        Line name
       VAR%FREQRES    Double         Frequency resolution
       VAR%IMAGFRE    Double         Image Frequency
       VAR%RESTFRE    Double         Rest Frequency
       VAR%VELRES     Real           Velocity resolution
       VAR%VELOFF     Real           Velocity offset
       VAR%F_AXIS     Integer        Frequency/Velocity axis
       VAR%DOPPLER    Real           Doppler factor
       VAR%VTYPE      Integer        Velocity type (code)

       ! Beam section
       VAR%BEAM       Integer        Length of section
       VAR%MAJOR      Real           Major axis of beam
       VAR%MINOR      Real           Minor axis of beam
       VAR%PA         Real           Position angle of beam

       ! Noise section
       VAR%SIGMA      Integer        Length of section
       VAR%NOISE      Real           Theoretical noise
       VAR%RMS        Real           Actual noise

       ! Proper motion section
       VAR%PROPER     Integer        Length of section
       VAR%MU         Real[2]        Along RA,DEC in mas/year
       VAR%PARALLAX   Real           Parallax in mas

       ! Telescope section
       VAR%TELE_SEC   Integer        Length of section
       VAR%NTEL       Integer        Number of telescopes
       ! For each telescope i=1 to NTEL:
       VAR%TELi%LON   Double         Telescope longitude
       VAR%TELi%LAT   Double         Telescope latitude
       VAR%TELi%ALT   Real           Telescope altitude [m]
       VAR%TELi%DIAM  Real           Telescope diameter [m]
       VAR%TELi%NAME  Char*12        Telescope name

    where  VAR  is the specified variable name for the header. VAR becomes a
    dummy variable of type header, which can only be referenced in a further
    DELETE /VARIABLE  command, in structure assignments through command LET,
    or in the HEADER command. The VAR%item variables  are  ReadOnly  if  the
    keyword  Key  is  READ, ReadWrite otherwise (including of course virtual
    headers), except for the dimension variables which cannot be modified.