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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.
healpixNestIndex( k, lon, lat )
- Gives the pixel index for a given sky position in the HEALPix
NEST scheme.
- Parameters:
k
(integer): HEALPix order (0..29)
lon
(floating point): longitude in degrees
lat
(floating point): latitude in degrees
- Return value
- (long integer): pixel index
healpixRingIndex( k, lon, lat )
- Gives the pixel index for a given sky position in the HEALPix
RING scheme.
- Parameters:
k
(integer): HEALPix order (0..29)
lon
(floating point): longitude in degrees
lat
(floating point): latitude in degrees
- Return value
- (long integer): pixel index
healpixNestLon( k, index )
- Returns the longitude of the approximate center of the tile
with a given index in the HEALPix NEST scheme.
- Parameters:
k
(integer): HEALPix order (0..29)
index
(long integer): healpix index
- Return value
- (floating point): longitude in degrees
healpixNestLat( k, index )
- Returns the latitude of the approximate center of the tile
with a given index in the HEALPix NEST scheme.
- Parameters:
k
(integer): HEALPix order (0..29)
index
(long integer): healpix index
- Return value
- (floating point): latitude in degrees
healpixRingLon( k, index )
- Returns the longitude of the approximate center of the tile
with a given index in the HEALPix RING scheme.
- Parameters:
k
(integer): HEALPix order (0..29)
index
(long integer): healpix index
- Return value
- (floating point): longitude in degrees
healpixRingLat( k, index )
- Returns the latitude of the approximate center of the tile
with a given index in the HEALPix NEST scheme.
- Parameters:
k
(integer): HEALPix order (0..29)
index
(long integer): healpix index
- Return value
- (floating point): latitude in degrees
healpixNestToRing( k, nestIndex )
- Converts a healpix ring index from the NEST to the RING scheme
at a given order.
- Parameters:
k
(integer): HEALPix order (0..29)
nestIndex
(long integer): pixel index in NEST scheme
- Return value
- (long integer): pixel index in RING scheme
healpixRingToNest( k, ringIndex )
- Converts a healpix ring index from the RING to the NEST scheme
at a given order.
- Parameters:
k
(integer): HEALPix order (0..29)
ringIndex
(long integer): pixel index in RING scheme
- Return value
- (long integer): pixel index in NEST 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.
- Parameters:
pixelsize
(floating point): pixel size in degrees
- Return value
- (integer): HEALPix order
k
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.
- Parameters:
k
(integer): HEALPix order (0..29)
- Return value
- (floating point): approximate angular resolution in degrees
healpixSteradians( k )
- Returns the solid angle in steradians of each HEALPix pixel
at a given order.
- Parameters:
k
(integer): HEALPix order (0..29)
- Return value
- (floating point): pixel size in steradians
- Examples:
healpixSteradians(5) = 0.0010226538585904274
4*PI/healpixSteradians(0) = 12.0
healpixSqdeg( k )
- Returns the solid angle in square degrees of each HEALPix pixel
at a given order.
- Parameters:
k
(integer): HEALPix order (0..29)
- Return value
- (floating point): pixel size in steradians
- Examples:
healpixSqdeg(5) = 3.357174580844667
round(12 * healpixSqdeg(0)) = 41253
steradiansToSqdeg( sr )
- Converts a solid angle from steradians to square degrees.
The unit sphere is 4*PI steradians = 360*360/PI square degrees.
- Parameters:
sr
(floating point): quantity in steradians
- Return value
- (floating point): quantity in sqare degrees
- Example:
round(steradiansToSqdeg(4*PI)) = 41253
sqdegToSteradians( sqdeg )
- Converts a solid angle from square degrees to steradians.
The unit sphere is 4*PI steradians = 360*360/PI square degrees.
- Parameters:
sqdeg
(floating point): quantity in square degrees
- Return value
- (floating point): quantity in steradians
- Example:
round(sqdegToSteradians(41253)/PI) = 4
htmLevel( pixelsize )
- Gives the HTM
level
parameter suitable for a given
pixel size.
- Parameters:
pixelsize
(floating point): required resolution in degrees
- Return value
- (integer): HTM level parameter
htmResolution( level )
- Gives the approximate resolution in degrees for a given HTM depth level.
- Parameters:
level
(integer): HTM depth
- Return value
- (floating point): approximate angular resolution in degrees
SQDEG
- Solid angle in steradians corresponding to 1 square degree.
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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page:
http://www.starlink.ac.uk/stilts/
Author email:
m.b.taylor@bristol.ac.uk
Mailing list:
topcat-user@jiscmail.ac.uk