Bits and pieces

[Stupendous Man <richmond@a188-l009.rit.edu>]

  Tom wrote:

> 1) Darks Don't Matter
> 2) Flats Don't Matter
> 3) The Sky Matters

 ...

>  Well, I think there is not so much experience by people 
>  using wide field instruments in lousy locations.

  Actually, there is a good deal of experience with such datasets --
but they come from photographic surveys, not electronic ones.
And therefore the data has rarely been processed to check
for the importance of various effects.  Even when it has, 
the photographic medium has prevented any variations less
than about 0.05 mag from appearing.

  I'm willing to agree to point 1.  I'm going to hold off on
point 2 until I can examine some of the results Tom is about to
send.  I agree wholeheartedly with point 3, given a wide-field
instrument surrounded by porch lights :-/

>   My preference would be for Michael R. to spend what time he 
>   has available studying how well my data matches the standard system.  Also 
>   now that I have a lot of stars measured over 500 days, how stable the 
>   transformations are.  So my largest interest is in what we can say about 
>   the quality of the data.

  That's my primary interest, too!

  In response to my comment

>>        d) the time it takes to reprocess a raw image is in the hours

Arne asked:

> Now, this I don't understand.  Why should it take hours to reprocess
> an image?  Please explain.

  My point was this: we have created tools which are designed to
take a night's worth of images and reduce them as a unit.  It 
currently takes Tom's computers hours to perform this step
for an entire night's images.

  I do NOT know if Tom has any tools which are designed to take
a single raw image and process it.  It would take _me_ some time
to figure out how to arrange the raw data in a way which would
cause the pipeline to do this.  If we don't keep the master
darks and flats created from this night's images, then we would
have to re-create them -- which takes minutes.  If we _do_ keep
the master darks and flats, why not keep the cleaned images, too?

  Arne continued:

> My basic point is that everyone agrees to save some kind of image.
> As long as the processing steps are archived somewhere, it should
> be only a matter of seconds to convert a raw image into a processed
> image, with absolute fidelity and leaving the original data intact.

  This is true only if

       a) we store the master darks and flats used to reduce a night's
               data together with the raw frames 

       b) we have a separate tool to perform basic image reduction
               on a single frame, and then analyze the cleaned frame

  The pipeline I wrote is not designed for step b).  One could
use IRAF or XVista or any commercial package to do this ... but one
would then _not_ get exactly the same results as the pipeline,
because the exact steps and parameters used won't be the same.

  On another note, Tom wrote:

> I just made 2 copies of the files to send to Michael S. (for the data base) 
> and Michael R.  (To look at the data quality).  It is a five disk set so I 
> don't really want to make a lot of copies.

  Chris A. said:

> How big are the files?  After compression.  Tabular
> data should compress well.  Maybe someone who has a
> good internet connection can put them on-line.

  I can put the entire dataset Tom is sending me into a directory
on my HTTP server here at RIT.  It may take bit of time to get it 
all arranged, but I believe I can make the files available by
around June 22 or so.

                                 Michael Richmond