Healpix for Science Tools

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Healpix for Science Tools

• Toby Burnett, Bruce Lesnick
• University of Washington

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The Healpix class an STL containers of Pixels

• Constructor set up nside (number of
  pixels)mode (nested or ring) and coord system
• begin() and end() methods return iterator that
  evaluate to pixels.
• Following code uses STL methods to create an image

MapParameters par(argc, argv)// defines image
parameters SkyImage piximage(par) // manage a
FITS image Healpix hpix(8) // create a Healpix
object, nside8 stdfor_each( h.begin(),
h.end(), DrawPixel(hix,piximage))
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HTM pixel directions
Level3512 pixels
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HEALPix pixel directions
nside8, 778 pixels
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The Pixel class nested in Healpix

• The constructor HealpixPixel(const
  astroSkyDir dir, const Healpix hp)creates a
  pixel containing the SkyDir direction dir, for
  the Healpix object hp.
• The methodHealpixPixeloperator astroSkyDir
  ()constreturns the pixel central direction as a
  SkyDir a Pixel behaves like a SkyDir.
• A pixel knows its
• direction
• Area (solid angle)
• Neighboring pixels (7 or 8)

Behave like
construct
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Image based on Healpix class HealpixData

• Simple wrapper of an array of pixel values and a
  Healpix object.
• Inherit from SkyImage, and that is it!

Display data from WMAP
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Status

• HTM and Healpix created to do integrals over the
  sphere.
• Also a good way to pixelate exposure functions,
  and bin the data for sky survey
• Class Healpix
• Using C code from WMAP
• Code to obtain neighbors converted from Fortran.
• Class HealpixData