Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/sas/6.5.0/doc/backscale/node9.html
Дата изменения: Tue Aug 16 09:21:28 2005
Дата индексирования: Sat Dec 22 10:09:50 2007
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XMM-Newton Science Analysis System


backscale (backscale-1.3.2) [xmmsas_20050815_1803-6.5.0]

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To improve the execution time of the task the source region is divided into a grid which is used to check whether pixels lie on a CCD. The width of each grid element is set to be 10 detector pixels ($\sim0.5$ arcseconds) for small regions (region half-width less than 2 arcminutes) and 20 detector pixels ($\sim1$ arcsecond) for larger regions. It has been chosen like this to give good coverage of CCD gaps where they make a significant contribution to the total area while keeping reasonable execution times for larger areas. This results in an execution time of $\sim$1 minute for a circular source region of 1 arcminute radius and $\sim$5 minutes for a circle of radius 5 arcminutes.