[daip] IMAGR channel binning problem

[Eric Greisen]

Eva Schinnerer wrote:
> Hi Eric,
> 
> Thanks very much for looking into this!
> 
> Here is the IMAGR input as Linda and I used it:
> 
> This is the call I used on the continuum subtracted UV data set to get  
> ngc2805_test.fits:
> 
> default 'imagr';sources 'ngc2805','';calcode '';freqid 1;qual -1
> timerang 0;selband -1;nfield 1;uvwtfn 'un';gain 0.1;bmaj 0
> selfreq -1;subarray 0;docalib -1;gainuse 2;dopol -1;blver -1;
> flagver 1;doband -1;bpver 1;smooth 0;stokes '';bchan 1;echan 0
> channel 0;bif 0;eif 0;outdisk 0;outseq 1;outver 0;in2name ''
> in2class '';in2seq 1;in2disk 0;do3dimag -1;fldsize 0;rashift 0
> decshift 0;uvtaper 0 0;uvrange 0 0;guard 0 0;rotate 0;zerosp 0
> uvsize 0 0;uvbox 0;uvbxfn 1;xtype 5;ytype 5;xparm 0;yparm 0
> bcomp 0;allokay 0;boxfile '';oboxfile '';minpatch 51;overlap 0
> phat 0;factor 0;cmethod '';imagrprm 0;ngauss 0;wgauss 0;fgauss 0
> maxpixel 0;bpa 0;bmin 0
> 
> outname 'ngc2805-test'
> cellsize 4
> imsize 512
> robust 5
> niter 0
> nboxes 1
> clbox 0
> flux 0
> nchav 2
> chinc 2
> dotv -1
> 
> getn 24
> go imagr
> 
> You can find the file that is causing the problems on my ftp-site at:
> 
> ftp.mpia.de/pub/schinner/am942_ngc2805_line_uvlin.fits
> 
> Thanks very much,
>       eva
> 
> 
> On May 23, 2009, at 5:29 PM, Eric Greisen wrote:
> 
>> Eva Schinnerer wrote:
>>> Hi Eric,
>>> Here is the promised email. We used the NCHAV and NINC set to 2 to  
>>> bin the velocity axis to increase the S/N in our HI data cube. The  
>>> original data cube looked fine, whereas the newly binned datacube  
>>> looked a continuum image. The data cube was continuum subtracted  
>>> with UVLIN.
>>> Please let me know if we only experienced this problem and I can  
>>> send you the data that caused this problem.
>>> Thanks very much,
>>>   eva
>> I tried this on my NGC6503 data set.  I ran IMAGR with NCHAV=2;  
>> CHINC=2 with both a gnu-compiler version and the faster Intel- 
>> compiler version which we send with binary installations.  I also  
>> then ran UVCOP with APARM(1) 1; NCHAV=2; CHINC=2 and reran IMAGR  
>> with NCHAV=1; CHINC=1.
>> All three produced nearly identical results, all of which looked fine.
>>
>> I guess I am going to need your data set and your inputs to IMAGR.
>

Okay - I fetched your data and ran IMAGR with NCHAV=1 and with NCHAV=2 
and also a SPLIT with NCHAV=2 followed by an IMAGR with NCHAV=1.

All produce approximately the same results.  You have not correctly 
subtracted the continuum source at the upper left.  It is so far from 
the phase center that a linear baseline fit was inadequate.  Not that 
you can use UVLSQ and try a higher order fit - but if this is the 
dominant source in the field - shifting it to the center would be better.

There is no problem with IMAGR.

Eric Greisen