Next Previous Up Contents
Next: Times
Up: General Functions
Previous: Strings

B.1.15 Tilings

Pixel tiling functions for the celestial sphere.

The k parameter for the HEALPix functions is the HEALPix order, which can be in the range 0<=k<=29. This is the logarithm to base 2 of the HEALPix NSIDE parameter. At order k, there are 12*4^k pixels on the sphere.

htmIndex( level, lon, lat )
Gives the HTM (Hierachical Triangular Mesh) pixel index for a given sky position.

healpixNestIndex( k, lon, lat )
Gives the pixel index for a given sky position in the HEALPix NEST scheme.

healpixRingIndex( k, lon, lat )
Gives the pixel index for a given sky position in the HEALPix RING scheme.

healpixNestLon( k, index )
Returns the longitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.

healpixNestLat( k, index )
Returns the latitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.

healpixRingLon( k, index )
Returns the longitude of the approximate center of the tile with a given index in the HEALPix RING scheme.

healpixRingLat( k, index )
Returns the latitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.

healpixNestToRing( k, nestIndex )
Converts a healpix ring index from the NEST to the RING scheme at a given order.

healpixRingToNest( k, ringIndex )
Converts a healpix ring index from the RING to the NEST scheme at a given order.

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.


Next Previous Up Contents
Next: Times
Up: General Functions
Previous: Strings

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@jiscmail.ac.uk