[daip] IMFIT output

[Eric Greisen]

Hans-Rainer Kloeckner wrote:
> Dear Eric,
> 
>     sorry for bothering you and I hope it will not eat up to much time 
> to answer my question.
> 
> Im running into a problem in the RA and DEC output of the task IMFIT
> 
> IMFIT1:   X-position        =   1525.617 +/-   0.0034 pixels
> IMFIT1:   Y-position        =    990.460 +/-   0.0036 pixels
> IMFIT1:                       RA 01 41 36.60758    +/-  0.0001825
> IMFIT1:                       DEC 21 08 53.5011    +/-   0.002681
> 
> Reading the values for the pixel offset of the MF table with 
> ParselTongue gives me
> 
> X = 1525.61657715
> Y = 990.460449219
> 
> and the Header information for RA and DEC of the image is
> 
> decinfo = [21.155416659760721, 1025.0, 0.00020802661310881376, 2048]
> rainfo  = [25.514416666666662, 1024.0, -0.00020802661310881376, 2048]
> 
> and calculating with
> 
> decindeg = decinfo[0] + ( y - decinfo[1] ) * decinfo[2]
> raindeg  = rainfo[0]  + ( x - rainfo[1] ) * rainfo[2]  / 
> cos(decindeg*(2*pi/360.))
> 
> the resulting RA is consistent with the RA output, BUT the Declination 
> is ~130 mas off !!!
> 
> RA    =  1, 41, 36.607591113516094
> DEC = 21, 8, 53.633450376233043)
> 
> Do I miss something here?

Yes - it is not the -GLS geometry but the -SIN geometry.  The 
computational form is different.  See The AIPS Memo Series (oldest one 
available from web) or the A&A paper II on WCS available from my web page
            http://www.aoc.nrao.edu~egreisen/

Eric Greisen