Michael Wood-Vasey and Joel Welling have been working on sampl;e subtraction of CFHT Megacam MOPS images to shake down subtractions, detection of transient events. Eventually we'll look at stacking. We're doing this in a database-free mode since there's an MWV-countable number of images.

Here's the basic process to start with a set of MEF files with a chip in each image in a directory 'proc/'.

First we make a set of tessellations.

skycells 8 -scale 0.2 -D CATDIR skycells

Extract an empty image with the WCS for the tesselation we want (skycell.0198755). I don't know how to figure out what this is for an arbitrary position on the sky. I'm sure there's an easy way; please add here.

dvoImageExtract skycell.0198755 -D CATDIR skycells -D CAMERA megacam -o skycell_0198755_warptemplate.fits mkdir skycell.0198755

Run a sample MEF file through (proc/906622.ch.fits)

pswarp -file proc/906622.ch.fits -mask proc/906622.ch.mk.fits -weight proc/906622.ch.wt.fits \

skycell.0198755/906622 skycell_0198755_warptemplate.fits -astrom proc/906622.cmf

And then run the last command for each of the .ch.fits files in proc/.

foreach base ( ls proc/*.ch.fits | sed -e 's/\..*//g' | sed -e 's/proc\///' ) foreach? pswarp -file proc/$base.ch.fits -weight proc/$base.ch.wt.fits -mask proc/$base.ch.mk.fits \

-astrom proc/$base.cmf skycell.0198755.new/$base skycell_0198755_warptemplate.fits -psf >& $base.log

foreach? end

This should generate a skycell.0918755 directory with images warped to the chosen tessellation.