[daip] fshift

[Eric Greisen]

Katherine Blundell wrote:
>
>> tget gethead
>> keyword 'xshift'
>> inp
> AIPS 1: GETHEAD:  Verb to read image header parameters into adverbs.
> AIPS 1: Adverbs     Values                 Comments
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: INNAME     'SS433_C0'              Image name(name).
> AIPS 1: INCLASS    'ICL001'                Image name(class).
> AIPS 1: INSEQ        20                    Image name(seq. #). 0=>high
> AIPS 1: INDISK        1                    Disk drive #. 0=>any
> AIPS 1: KEYWORD    'XSHIFT'                Name of header parameter.
> AIPS 1:                                    See EXPLAIN GETHEAD for list.
>> go gethead
>> print keyvalue
> AIPS 1: (  1)  5.89250249E-09     0
>> keyword 'yshift'
>> go gethead
>> print keyvalue
> AIPS 1: (  1)     0.000000064     0
> 
> Sorry to be making heavy weather of this, but this is really puzzling me.

These are in degrees so = 21 and 230 micro arc sec and the XShift has a 
/ cos(dec) in it so the 21 is multiplied by cos(dec) before being added 
to the shift found in the JMFIT.  The FSHIFT that is returned is the net 
shift to use next time = previous shift + fit value.

Eric