want image center in WCS units

Blaise Canzian wrote on Aug 21, 2004

I have an image with a correct WCS in the header.  I would like to know 
if there is an IRAF application or series of applications that will 
provide a centroid of an image and return the answer to me in the WCS 
frame (RA and Dec), not pixels.  Or if, having computed the cetroid in 
pixel units, I can feed that coordinate to an application that returns 
(RA,Dec) based on the image WCS.  Thanks.

-- Blaise Canzian
    blaise@nofs.navy.mil

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Francisco Valdes wrote on Aug 23, 2004

Blaise Canzian wrote:
> I have an image with a correct WCS in the header.  I would like to know 
> if there is an IRAF application or series of applications that will 
> provide a centroid of an image and return the answer to me in the WCS 
> frame (RA and Dec), not pixels.  Or if, having computed the cetroid in 
> pixel units, I can feed that coordinate to an application that returns 
> (RA,Dec) based on the image WCS.  Thanks.
> 
> -- Blaise Canzian
>    blaise@nofs.navy.mil
> 


Hello Blaise,

Whether tasks report coordinates in world units rather than pixels 
depends on the application.  However, a very useful task, which answers 
one of you questions is WCSCTRAN.  This converts between "world" (which 
is whatever is in the header such as RA/DEC) and "logical" (which means 
pixels).  So if you collect a series of pixel coordinates in a text file 
you can easily convert them to RA/DEC as defined in the image header 
with this task.

Yours,
Frank Valdes
IRAF Group

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Howard Bushouse wrote on Aug 24, 2004

> Blaise Canzian wrote:
> > I have an image with a correct WCS in the header.  I would like to know
> > if there is an IRAF application or series of applications that will
> > provide a centroid of an image and return the answer to me in the WCS
> > frame (RA and Dec), not pixels.  Or if, having computed the cetroid in
> > pixel units, I can feed that coordinate to an application that returns
> > (RA,Dec) based on the image WCS.  Thanks.
> >
> > -- Blaise Canzian
> >    blaise@nofs.navy.mil
> >
>
>
> Hello Blaise,
>
> Whether tasks report coordinates in world units rather than pixels
> depends on the application.  However, a very useful task, which answers
> one of you questions is WCSCTRAN.  This converts between "world" (which
> is whatever is in the header such as RA/DEC) and "logical" (which means
> pixels).  So if you collect a series of pixel coordinates in a text file
> you can easily convert them to RA/DEC as defined in the image header
> with this task.
>
> Yours,
> Frank Valdes
> IRAF Group
>
>

There're also the tasks "rd2xy" and "xy2rd" somewhere in STSDAS that
do conversions to/from RA-Dec and x/y pixel coords, based on header
WCS info.

-Howard Bushouse
  STScI STSDAS Group

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Last post on Aug 24, 2004