[daip] Re: beam patch

[Crystal Brogan]

On Mon, 1 Nov 2004, Eric Greisen wrote:

> Crystal Brogan writes:
>  >
>  > Hi Eric,
>  >
>  > I hope all is well with you? I wondered if you could explain
>  > a warning message that I see frequently in IMAGR when I'm
>  > doing 3-D cleaning of complex Galactic plane fields.
>  >
>  > IMAGR1: CDECID: CANNOT OBTAIN BEAM PATCH - MAP LIMIT PROPERLY
>  >
>  > After stating this, it seems to go on cleaning more or less normally. It
>  > seems to happen when a "remake images"  command is needed but has not yet
>  > been triggered internally.  i.e. if I give an explicit remake images
>  > command through the TV this warning goes away (for awhile).
>  >
>  > What does it mean? Is it detrimental?
>
> Yes - I am suprised that there are not then messages like loaded too
> many points to the AP memory.  The comment in the code says
>
> C                                       If program gets here there is a
> C                                       serious problem. e.g. residual
> C                                       map has a constant (or nearly)
> C                                       value, set NRESKP.
>       KPAT = MINPCH - 1
> C                                       Use next to highest bin
>       JLEV = NBMHIS - 1
> C                                       Let user know
>       MSGTXT = 'CDECID: CANNOT OBTAIN BEAM PATCH - MAP LIMIT PROPERLY'
>       CALL MSGWRT (8)
>
> It occurs to me that you are perhaps Cleaning large numbers of facets
> over big areas - to what have you set MAXPIXEL?  I suspect that
> something substantially bigger than the default may be appropriate for
> what you are doing - how many pixels are in the Clean boxes?
>

It is certainly a big image. 74 MHz A+B+C+D. There are 79, 512 pixel
facets and 3 resolutions for a total of 237.

I have maxpixel set to 60,000

Actually I think I'm going to have to try something else anyway.  Perhaps
SDI. After numerous trials I cannot get multiscale clean to "do the right
thing" on this 74 MHz image that has both strong emission and absorption.
I keep getting weird "ghost" holes where there isn't any absorption. This
is happening during cleans on the larger resolution images. This happens
no matter how much I try to change the parameters to favor the highest
resolution (increasing imagrprm(11) and fgauss clean cutoff). In
fact it is barely cleaning on large scales at all now but I still
get the artifacts. Any ideas? These are my parameters (I took out
lines that are default to make it shorter):

AIPS 2: CELLSIZE     15          15        (X,Y) size of grid in asec
AIPS 2: IMSIZE      512         512        Minimum image size
AIPS 2: NFIELD       79                    Number of fields (max 4096)
AIPS 2: DO3DIMAG      1                    > 0 => use different tangent
AIPS 2:                                    points for each field
AIPS 2: GAIN          0.1                  Clean loop gain
AIPS 2: FLUX          0                    Minimum Clean component (Jy)
AIPS 2: MINPATCH    121                    Min. BEAM half-width in AP.
AIPS 2: OVERLAP       2                    1 => restore components to
AIPS 2: IMAGRPRM      0           0        Task enrichment parameters
AIPS 2:               0           0        (1) Antenna diameter (m)
AIPS 2:               0           0        (2) Source Spectral index
AIPS 2:               0           0        (3) Frequency scaling factor
AIPS 2:               0           0        (4) > 0 -> SDI Clean factor
AIPS 2:               0.7      1.000E-04   (5) >0 => scale residuals
AIPS 2:              0.05        0.05      (6) Half-width in x of box
AIPS 2:              0.05         0        (7) Half-width in y of box
AIPS 2:               0           0        (8) Filter components whose
AIPS 2:               0           1.1      neighborhood is weaker than
AIPS 2:                                    IMAGRPRM(8) Jy.  0 -> don't
AIPS 2:                                    (9) Radius in pixels for the
AIPS 2:                                    IMAGRPRM(8) test.
AIPS 2:                                    (10) multiplier of image size
AIPS 2:                                    to get beam size: 0 => 2;
AIPS 2:                                    2, 1, 0.5 0.25 supported
AIPS 2:                                    (11-16) Multi-resolution
AIPS 2:                                    added controls
AIPS 2:                                    (19) Dynamic range limit
AIPS 2:                                    (20) Retry factor (see help)
AIPS 2: NGAUSS        3                    Number of resolutions to use
AIPS 2: WGAUSS        0         375        Resolutions in arc sec >= 0
AIPS 2:            1125        *rest 0
AIPS 2: FGAUSS        1          10        Minimum flux for each resol.
AIPS 2:             150        *rest 0
AIPS 2: MAXPIXEL   60000

> PS This was my first day back after a week's trip to ADASS and some
> birding.

I hope it was fun (the birding at least).


-c