[alma-config] Difference images TNG

[Steven]

Hello.

 In response to Bryan and Mark's queries, all the images are treated the
same when CLEANing, i.e. no masks, no boxes, no initial models. By way of an
example, below is an extract of the batch file for CLEANing the KBM51_4-23B7
case. Note however that much of the sensible defaults are embodied in the
nuvco3mm parameter set. The parameters used are hopefully as decided by
consensus.

Now having said that all images are treated the same, there is no problem
with using model-specific parameter sets when CLEANing. In the batch file
extract below you will note that some adverbs are in upper case- these are
read in from an external file of CLEAN parameters, which may be specified on
a per-model basis in the setup file that my scripts use to create the batch
file (the parameters shown are read in by default when the input file is
specified as 'none').  As the external file is read immediately before
running IMAGR any of that task's adverbs may be modified at this point.

So if it is necessary and desirable to redo all the CLEANing using initial
models and CLEAN boxes, fine, although abviously the less the better!
Speaking as a relative novice at this game, if the Mars results are poor
because of lack of short spacings and show no distinction between the K and
C configurations, is that not the bottom line... i.e. worry about Mars at
other resolutions rather than using CLEAN to make a silk purse out of a sows
ear. (I'm sure there is more to it than that, I'm just hoping someone will
tell me!)

Moving along to the metrics as discussed at the last telecon, I have done a
few FFTs (I presume we are interested in power spectra rather than
considering real and imaginary components). Also I have found an excellent
AIPS task (IMEAN) which allows me to export image statistics and indeed
histogram data to a named file, thus allowing max, min, and rms data to be
listed with plots in the future.I have also been looking at calculating
Fidelity images and their histograms as highlighted by Stephane, and also
Leonia's 'fidelity-range' measure, and this all seems fairly
straightforward.
This essentially uses IMSTAT or IMEAN to yield the rms of the difference
image already calculated, IMCLP to apply the 0.7x rms threshold to the
abs(difference image), COMB to calculate the ratio, and IMEAN to reveal the
histogram and new rms etc.

The same principles can be employed to calculate John's metrics of rms
values for a series of (difference image)/(convolved model magic blanked at
a certain level), assuming 'magic blanked' is synonymous with 'brutally
thresholded'!

So I am in the position to
    a) produce FFTs of difference images
    b) generate fidelity images and associated numbers
    c) calculate John's metric
    d) redo CLEANing with new parameters, for some/all images at some/all
resolutions
whilst also thinking about
    e) try some MEM deconvolutions

e) looks in jepoardy just now, but some indication of priority for the
others would be useful along with parameters and/or initial models for d).
In the meantime I will start scripting a) b) and c), and will probably
produce some initial results for your perusal.

Cheers,
       Steven


Extract of batch file for CLEANing
===========================
version 'myaips'
prnumber 0
prtask 'imagr'
go clrmsg
prtask ' '
get nuvco3mm
cellsize 0.02
inname 'KBM51_4-23b7'
inclass 'nuvco'
inseq 0
indisk 0
bchan 0
outname ' '
outseq 0
outdisk 11
in2name ' '
in2class ' '
in2seq 0
in2disk 11
selfreq 345000
NITER 10000
NBOXES 0
CLBOX 0
GAIN 0.1
MINPATCH 256
BMAJ 0.101
BMIN 0.101
BPA 0
PHAT 0
FACTOR 0
CPARM 12,0
go imagr
inclass 'ICLN'
inseq 0
blc 256
trc 768
plev 0
outfile 'myarea:KBM51_4-23b7.ICLN.PS'
go cntr
functype 'NE'
go lwpla
outfile 'myarea:KBM51_4-23b7.ICLN2.PS'
go grey
functype 'NE'
go lwpla
functype 'LN'

Steven Heddle, Newington, Holm Road, Kirkwall, Orkney KW15 1PY
Tel: 01856 877119             Email: steven at heddle97.freeserve.co.uk
Fax: 0870 4039359           URL: http://www.heddle97.freeserve.co.uk