= Heather's stacking adventures =

This wiki describes my adventures while trying to stack things in both skyprobe and in gpc1.

I am trying to process skyprobe images using ppStack. This has not been done before, but I have a wiki to describe some of my steps (see [wiki:IspSasProcessing]).  The stacks look pretty crummy, which led to the following investigations:

 1. why are there big chunks missing
 2. why did it take 10k seconds?
 3. why are the edges nan'd off

These are stacks of roughly 100-200 skyprobe warps (in a special skyprobe tessalation where the pixel size is the size of a skyprobe pixel, and the 'skycell' is the size of a projection cell. The first investigation (why are there big chunks missing) I answered by writing a tool (in ipptrunk/tools/heather/stack_inspector.pl) - give it a stack_id, it will make binned fits of the stack and the input warps. You can easily open up the stack and all the inputs, which I did with skycell 1315 (g band).  What I found out is that everything is covered multiple times. The skycell should be completely filled with pixels.

At this point, I committed a sin: I downloaded IRAF to see if it could stack better. I did the dumbest stack possible (I fed it 200 images and said, go make a stack). IRAF complied and gave me a stack ~ 1 minute later, completely filled, very deep, very nice:

[[Image(stuff.png)]]

Next was to play with gpc1 images with IRAF for SAS. I downloaded a random g band skycell ( skycell.1495.014 ), grabbed the inputs, and stacked.  I discovered 2 things:

 1. Iraf doesn't like compressed files
 2. Iraf doesn't like different bzero and bscale.  

Ken played with IRAF, and got a better IRAF stack:
{{{
Apr  1 12:15: IMCOMBINE
  combine = median, scale = none, zero = none, weight = none
  reject = avsigclip, mclip = yes, nkeep = 1
  lsigma = 3., hsigma = 2.5
  lthreshold = -1000., hthreshold = 1000.
  blank = 0.
                Images 
  /home/heather/sas_v8_stacks/o5745g0409o.356779.wrp.453852.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5745g0421o.356794.wrp.453876.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5745g0432o.356807.wrp.453888.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5745g0442o.356814.wrp.453903.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5746g0418o.357453.wrp.453912.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5746g0428o.357464.wrp.453927.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5746g0441o.357477.wrp.453937.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5746g0450o.357486.wrp.453947.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5748g0357o.358780.wrp.453989.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5748g0368o.358778.wrp.454010.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5748g0379o.358756.wrp.453971.skycell.1495.014.fun.fits
  /home/heather/sas_v8_stacks/o5748g0389o.358765.wrp.453992.skycell.1495.014.fun.fits

  Output image = sastestkenmed2, ncombine = 12
}}}

Here is a comparison of IRAF to IPP for gpc1

[[Image(stuff.png)]]