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### B.1.1 Tilings

Pixel tiling functions for the celestial sphere.

htmIndex( level, ra, dec )
  Gives the HTM (Hierachical Triangular Mesh) pixel index for a given sky position.
healpixNestIndex( k, ra, dec )
  Gives the pixel index for a given sky position in the HEALPix NEST scheme.
healpixRingIndex( k, ra, dec )
  Gives the pixel index for a given sky position in the HEALPix RING scheme.
healpixK( pixelsize )
  Gives the HEALPix resolution parameter suitable for a given pixel size. This `k` value is the logarithm to base 2 of the Nside parameter.
healpixResolution( k )
  Gives the approximate resolution in degrees for a given HEALPix resolution parameter `k` This `k` value is the logarithm to base 2 of the Nside parameter.
healpixSteradians( k )
  Returns the solid angle in steradians of each HEALPix pixel at a given order.
healpixSqdeg( k )
  Returns the solid angle in square degrees of each HEALPix pixel at a given order.
steradiansToSqdeg( sr )
  Converts a solid angle from steradians to square degrees.

  The unit sphere is 4*PI steradians = 360*360/PI square degrees.

sqdegToSteradians( sqdeg )
  Converts a solid angle from square degrees to steradians.

  The unit sphere is 4*PI steradians = 360*360/PI square degrees.

htmLevel( pixelsize )
  Gives the HTM `level` parameter suitable for a given pixel size.
htmResolution( level )
  Gives the approximate resolution in degrees for a given HTM depth level.
SQDEG
  Solid angle in steradians corresponding to 1 square degree.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@bristol.ac.uk