Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/sas/5.4.1/doc/region/node8.html
Дата изменения: Fri Jan 10 22:46:38 2003
Дата индексирования: Sat Dec 22 07:48:16 2007
Кодировка:
Поисковые слова: cassini spacecraft

XMM-Newton Science Analysis System


region (region-6.2.2) [xmmsas_20030110_1802-5.4.1]

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Algorithm

   module region_mod

     subroutine region

        get parameters;

        open source list;

        foreach source
          transform celestial coordinates to sky location;
          calculate initial estimated extraction radius;
          calculate distance to nearest neighbour;
        loop

        sort sources in ascending order of nearest neighbour separation;
        initialise array of flags;

        ; First pass considering just nearest-neighbour pairs
        foreach source in sorted list
          if(region overlaps with nearest neighbour)
            if(neighbour has been reduced)
              newradius = half distance to neighbour;
            else
              newradius = distance to neighbour - neighbour radius;
            endif
          endif
          set altered flag;
        loop

        ; Second pass considering all pairs
        foreach source
          foreach other source
            calculate separation of pair of sources;
            if(separation < sum of extraction radii)
              size of larger region = separation - size of smaller region;
            endif
          loop
        loop

        foreach source
          clip source extraction regions to the field-of-view by
                reducing size of extraction region;

          if(newradius < minimum radius)
            issue warning;
            reset to minimum radius;
          endif
        loop

        ; Background region
        calculate inner and out radii of background annulus;
        determine overlap of background with nearby source regions;
        exclude overlapping source extraction regions from background region;
        clip background extraction regions to the field-of-view;

        transform sky location to event coordinates ("sky pixels");

        write source region to source region file;
        write background region to background region file;

     end subroutine region

   end module region_mod