[[PageOutline]]

= Outline =

This page outlines an investigation into the cross-matching used by the Durham group to generate the 'true positives' and 'false positives' data subsets. Durham used TOPCAT to perform the cross-match, and presented the results as FITS files. Our aim is to reproduce the same results as Durham then experiment with different cross-matching parameters. 

= Durham-supplied data =

Durham supplied the following files (FITS binary table format) for analysis.

|| '''File''' || '''Rows''' || '''Comments''' ||
|| footprint-stripe82.fits|| 449,254 || Sloan Stripe 82 master file||
|| footprint-g-all-psphot.fits.bz2 || 282,604|| all IPP g filter||
|| footprint-r-all-psphot.fits.bz2|| 278,280 || all IPP r filter||
|| footprint-i-all-psphot.fits.bz2|| 320,655 || all IPP i filter||
|| footprint-z-all-psphot.fits.bz2|| 258,130|| all IPP z filter||
|| footprint-y-all-psphot.fits.bz2|| 175,578 || all IPP y filter||
|| footprint-g-not-matched-psphot.fits.bz2 || 171,973 || all IPP false detections in g ||
|| footprint-r-not-matched-psphot.fits.bz2|| 67,455 || all IPP false detections in r ||
|| footprint-i-not-matched-psphot.fits.bz2|| 59,973 || all IPP false detections in i ||
|| footprint-y-not-matched-psphot.fits.bz2|| 46,729 || all IPP false detections in z ||
|| footprint-z-not-matched-psphot.fits.bz2|| 51,391|| all IPP false detections in y ||


= Durham method =

Durham used TOPCAT to perform the cross-matching. They used the following settings:

 * 'Algorithm' : Sky
 * 'Max Error' : 1.0 arcsec
 * 'Match Selection' : Best Match Only

It is thought (by Nigel Metcalfe) that Peter Draper cut the Sloan data on BINNED1=true. I applied this cut, and it only removed 428 sourced out of a total of 449,254.

The results of the Durham crossmatching are as follows:

|| Total IPP detections || 1,315,247 || 
|| True positives || 917,726 ||
|| False positives || 397,521 ||
 
== Attempts to replicate the Durham method ==

Using TOPCAT with the same data and same settings as Durham, we get the following:


|| Total IPP detections || 1,315,247 || 
|| True positives || 268,044 ||
|| False positives || 1,047,203 ||