ECHFIND-Locate spectra in echelle data

Description:

Find orders within an echelle image and optionally write a mask image that can be used for quick-look extraction of orders from a raw echelle image.

Parameters:

IMAGE

Name of echelle image in which to search.

PERISCOPE

Is the periscope fitted?

YSTART

Y value to start search for orders.

YEND

Y value to stop search for orders.

MSTART

Number of the first order in range.

MDELTA

Order number increment (-1 or +1).

SDIST

Write output file SDIST.DAT in SDIST format?

OUTFILE

Name of output report file.

THRESH

Threshold above which orders are deemed to exist.

MINHW

Minimum half-width of orders.

DOMASK

Create an output mask image?

OUTPUT

Name of mask image showing order positions.

Source comments:

 E C H F I N D

 Program name:
    ECHFIND

 Function:
    Find orders within an echelle image and optionally write a mask
    image that can be used for quick-look extraction of orders from a
    raw echelle image.

 Description:
    Note: This program is believed to work, but it has not been as
    extensively used and tested as has the ICUR/SDIST method.
    ICUR/SDIST is believed to be a superior if slightly less
    convenient way of locating and tracking orders. Having said this,
    you are welcome to try this program!

    The program can be run in several different ways. The SDIST
    keyword controls whether an SDIST.DAT file (which can later be
    used by CDIST) is created and the DOMASK keyword controls whether
    a mask image (that can later be applied by MASKEXT) is created.

    The program locates the orders by taking a vertical cut (i.e. in the
    cross-dispersion direction) through the data (averaging 7 columns)
    and then searches for peaks occurring above a user-specified
    threshhold.  Unfortunately this threshhold has to be a constant
    and this, plus knowing a sensible value to give for it, is one of
    the major limitations of the program.

    Having located the orders, they are tracked using a method that is
    a combination of edge detection and centroiding. Little of the
    feedback and control that is available with SDIST is available and
    this is another major problem.

    Having tracked the orders, the SDIST.DAT file is written if
    requested.  If an SDIST.DAT file is not required, a more
    user-readable listing file is written. Finally, the mask image is
    written if requested.  The values in the mask are set to be zero
    if that pixel in the mask does not lie in an order and to a number
    derived from the order number otherwise (see below). It is
    guaranteed that every order is extracted using the same number of
    rows, but of course the position of these rows may vary along an
    order so one can expect visible jumps in the extracted data,
    especially if too fews rows are extracted to take all the data
    from the object.

    The PERISCOPE keyword (see below) determines whether each order
    has two separate parts (corresponding to object and sky and due to
    the special periscope that samples object and sky at a wide
    spacing and brings them together on the slit) or one part
    (corresponding simply to the slit).  The data values in the mask
    are 10 * (true order number) + (sub-order number) where the
    sub-order number is 0 if there is no periscope fitted, 1 if this
    is the first part of an order and 2 if this is the second part of
    the order. The "first" and "second" parts of an order are defined
    so that the actual data values in the mask are monotonic along a
    vertical slice through it, i.e. they might go 412, 411, 402, 401 if
    the periscope is fitted and they might go 410, 400 if it is not
    fitted.

    If PERISCOPE is NO, then unlike in ECHMASK, the user has no
    option of splitting the data in an order into object and sky.
    There is room for enhancement here.

 Parameters:

    (>) IMAGE         (File) The name of the raw echelle image.
    (>) YSTART        (Integer) The starting and ending Y positions to
    (>) YEND          (Integer) search for orders. Default entire image.
    (>) PERISCOPE     (Keyword) Whether or not the periscope is fitted.
                      Default YES.
    (>) MSTART        (Integer) The order number of the first
                      "spectrum" in the coefficient file. Default 1.
    (>) MDELTA        (Integer) +1 if order numbers increase as
                      "spectrum number" increased, -1 otherwise.
                      Default -1.
    (>) SDIST         (Keyword) Whether to write an SDIST.DAT file.
                      Default NO.
    (>) OUTFILE       (Character) If SDIST is NO, the name of the
                      listing file.
    (>) THRESH        (Real) The threshhold above which peaks in the
                      profile across the orders must lie in order to
                      be considered as order peaks. Default 1000.
    (>) MINHW         (Integer) The half width that is used for the
                      median filter that is passed through the
                      profiles to remove rogue data before looking for
                      orders. Default 5.
    (>) DOMASK        (Keyword) Whether to write a mask image. Default
                      NO.
    (<) OUTPUT        (File) If DOMASK is YES, the name of the mask
                      image. Default MASK.

 Language:
    FORTRAN

 External variables used:

    None

 Prior requirements:
    None

Authors:

William Lupton, AAO