[daip] Problems with COWINDOW

[Eric Greisen]

Roland Karlsson wrote:
> Dear Dr Greisen,
> 
> I have problems to shift the center coordinate of an image. I want to 
> shift the center coordinates to the Galactic Center by changing the 
> coordinates (COORDINATE) in the COWINDOW program. However, the 
> imagecenter becomes shifted to another position, than the input in 
> COWINDOW. It also seems that the amount of shift varies when IMSIZE is 
> changed. We use the AIPS 31DEC08, and inputs and IMH are as below. The 
> data were concatenated from two VLA data sets. I could not find any help 
> in the Cookbook or on the blog, and I am currently the only AIPS user 
> here. What is wrong?
> 
> Thanks,
> Roland Karlsson
> Stockholm University
> 
> coordina 17 42 29.3, -28 59 18.6
>  >inp cowin
> 
> COWINDOW:  Verb to set window centered on a coordinate
> AIPS 1: Adverbs     Values                 Comments
> AIPS 1: ----------------------------------------------------------------
> AIPS 1:           Input adverbs
> AIPS 1: USERID     1071                    User ID. 0=>current user
> AIPS 1:                                      32000=>all users
> AIPS 1: INNAME     '67+65CONT'             Image name(name).
> AIPS 1: INCLASS    'ICL001'                Image name(class).
> AIPS 1: INSEQ         1                    Image name(seq. #). 0=>high
> AIPS 1: INDISK        1                    Disk drive #. 0=>any
> AIPS 1: COORDINA     17          42        Coordinate in image
> AIPS 1:              29.3       -28          59          18.6
> AIPS 1: IMSIZE        0           0        X,Y size to include
> AIPS 1:                                      0=>entire centered image
>  >
> go cowin
>  >
>                                  
>  >imcen
> AIPS 1: Map pixel position:   710.63  364.13
> AIPS 1: Skypos: RA 17 42 29.809  DEC -28 58 53.79
> AIPS 1: Skypos: IPOL  1666.097 MHZ
>  >
> 
> Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
> AIPS 1: RA---SIN  1024    17 42 57.057     512.00         -1.800    0.00
> AIPS 1: DEC--SIN  1024   -28 54 26.000     513.00          1.800    0.00
> AIPS 1: FREQ         1   1.6660968E+09       1.00  4.8828125E+04    0.00
> AIPS 1: STOKES       1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Coordinate equinox 1950.00
> AIPS 1: Map type=NORMAL              Number of iterations=    3339
> AIPS 1: Conv size=   6.52 X   5.00   Position angle=  28.34
> AIPS 1: Observed RA   17 42 30.000    DEC -28 59 30.00
> AIPS 1: Phase shifted in X    405.858  in Y    304.000
> AIPS 1: Rest freq   1667.359         Vel type: OPTICAL wrt YOU
> AIPS 1: Alt ref. value -3.80000E+04  wrt pixel   32.00
> 
> 

What do you think COWINDOW is supposed to do?  It is a verb (a piece of 
a subroutine inside AIPS.EXE itself) that looks at an image header and a 
stated coordinate and sets the adverbs BLC and TRC which are in pixels 
accoridingly.  That is all - set 2 adve3rbs - not change your image.

The best way to change coordinates is to use UVFIX ahead of the imaging.
See its help file for a suggestion of running it twice for the most 
accurate results.

OHGEO may be used to regrid your image on another projection including a 
-SIN projection with a new reference pixel value.

Eric Greisen