Class Tilings
- java.lang.Object
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- uk.ac.starlink.ttools.func.Tilings
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public class Tilings extends java.lang.Object
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 orderk
, there are 12*4^k pixels on the sphere.- Since:
- 6 Dec 2007
- Author:
- Mark Taylor
- See Also:
- HTM web site, HEALPix web site
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Field Summary
Fields Modifier and Type Field Description static double
SQDEG
Solid angle in steradians corresponding to 1 square degree.
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Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description static int
healpixK(double pixelsize)
Gives the HEALPix resolution parameter suitable for a given pixel size.static long
healpixNestIndex(int k, double lon, double lat)
Gives the pixel index for a given sky position in the HEALPix NEST scheme.static double
healpixNestLat(int k, long index)
Returns the latitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.static double
healpixNestLon(int k, long index)
Returns the longitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.static long
healpixNestToRing(int k, long nestIndex)
Converts a healpix ring index from the NEST to the RING scheme at a given order.static double
healpixResolution(int k)
Gives the approximate resolution in degrees for a given HEALPix resolution parameterk
Thisk
value is the logarithm to base 2 of the Nside parameter.static long
healpixRingIndex(int k, double lon, double lat)
Gives the pixel index for a given sky position in the HEALPix RING scheme.static double
healpixRingLat(int k, long index)
Returns the latitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.static double
healpixRingLon(int k, long index)
Returns the longitude of the approximate center of the tile with a given index in the HEALPix RING scheme.static long
healpixRingToNest(int k, long ringIndex)
Converts a healpix ring index from the RING to the NEST scheme at a given order.static double
healpixSqdeg(int k)
Returns the solid angle in square degrees of each HEALPix pixel at a given order.static double
healpixSteradians(int k)
Returns the solid angle in steradians of each HEALPix pixel at a given order.static int
htmLevel(double pixelsize)
Gives the HTMlevel
parameter suitable for a given pixel size.static double
htmResolution(int level)
Gives the approximate resolution in degrees for a given HTM depth level.static double
sqdegToSteradians(double sqdeg)
Converts a solid angle from square degrees to steradians.static double
steradiansToSqdeg(double sr)
Converts a solid angle from steradians to square degrees.
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Field Detail
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SQDEG
public static final double SQDEG
Solid angle in steradians corresponding to 1 square degree.- See Also:
- Constant Field Values
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Method Detail
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healpixNestIndex
public static long healpixNestIndex(int k, double lon, double lat)
Gives the pixel index for a given sky position in the HEALPix NEST scheme.- Parameters:
k
- HEALPix order (0..29)lon
- longitude in degreeslat
- latitude in degrees- Returns:
- pixel index
- See Also:
- HEALPix web site
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healpixRingIndex
public static long healpixRingIndex(int k, double lon, double lat)
Gives the pixel index for a given sky position in the HEALPix RING scheme.- Parameters:
k
- HEALPix order (0..29)lon
- longitude in degreeslat
- latitude in degrees- Returns:
- pixel index
- See Also:
- HEALPix web site
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healpixNestLon
public static double healpixNestLon(int k, long index)
Returns the longitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.Note: the
index
parameter is 0-based, unlike the table row index special token$index
(a.k.a.$0
), which is 1-based. So if the HEALpix index is implicitly determined by the table row, the value$index-1
should be used.- Parameters:
k
- HEALPix order (0..29)index
- healpix index- Returns:
- longitude in degrees
- See Also:
- HEALPix web site
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healpixNestLat
public static double healpixNestLat(int k, long index)
Returns the latitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.Note: the
index
parameter is 0-based, unlike the table row index special token$index
(a.k.a.$0
), which is 1-based. So if the HEALpix index is implicitly determined by the table row, the value$index-1
should be used.- Parameters:
k
- HEALPix order (0..29)index
- healpix index- Returns:
- latitude in degrees
- See Also:
- HEALPix web site
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healpixRingLon
public static double healpixRingLon(int k, long index)
Returns the longitude of the approximate center of the tile with a given index in the HEALPix RING scheme.Note: the
index
parameter is 0-based, unlike the table row index special token$index
(a.k.a.$0
), which is 1-based. So if the HEALpix index is implicitly determined by the table row, the value$index-1
should be used.- Parameters:
k
- HEALPix order (0..29)index
- healpix index- Returns:
- longitude in degrees
- See Also:
- HEALPix web site
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healpixRingLat
public static double healpixRingLat(int k, long index)
Returns the latitude of the approximate center of the tile with a given index in the HEALPix NEST scheme.Note: the
index
parameter is 0-based, unlike the table row index special token$index
(a.k.a.$0
), which is 1-based. So if the HEALpix index is implicitly determined by the table row, the value$index-1
should be used.- Parameters:
k
- HEALPix order (0..29)index
- healpix index- Returns:
- latitude in degrees
- See Also:
- HEALPix web site
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healpixNestToRing
public static long healpixNestToRing(int k, long nestIndex)
Converts a healpix ring index from the NEST to the RING scheme at a given order.Note: the
nestIndex
parameter is 0-based, unlike the table row index special token$index
(a.k.a.$0
), which is 1-based. So if the HEALpix index is implicitly determined by the table row, the value$index-1
should be used.- Parameters:
k
- HEALPix order (0..29)nestIndex
- pixel index in NEST scheme- Returns:
- pixel index in RING scheme
- See Also:
- HEALPix web site
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healpixRingToNest
public static long healpixRingToNest(int k, long ringIndex)
Converts a healpix ring index from the RING to the NEST scheme at a given order.Note: the
ringIndex
parameter is 0-based, unlike the table row index special token$index
(a.k.a.$0
), which is 1-based. So if the HEALpix index is implicitly determined by the table row, the value$index-1
should be used.- Parameters:
k
- HEALPix order (0..29)ringIndex
- pixel index in RING scheme- Returns:
- pixel index in NEST scheme
- See Also:
- HEALPix web site
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healpixK
public static int healpixK(double pixelsize)
Gives the HEALPix resolution parameter suitable for a given pixel size. Thisk
value is the logarithm to base 2 of the Nside parameter.- Parameters:
pixelsize
- pixel size in degrees- Returns:
- HEALPix order
k
- See Also:
- HEALPix web site
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healpixResolution
public static double healpixResolution(int k)
Gives the approximate resolution in degrees for a given HEALPix resolution parameterk
Thisk
value is the logarithm to base 2 of the Nside parameter.- Parameters:
k
- HEALPix order (0..29)- Returns:
- approximate angular resolution in degrees
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healpixSteradians
public static double healpixSteradians(int k)
Returns the solid angle in steradians of each HEALPix pixel at a given order.- Parameters:
k
- HEALPix order (0..29)- Returns:
- pixel size in steradians
- Examples:
healpixSteradians(5) = 0.0010226538585904274
,4*PI/healpixSteradians(0) = 12.0
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healpixSqdeg
public static double healpixSqdeg(int k)
Returns the solid angle in square degrees of each HEALPix pixel at a given order.- Parameters:
k
- HEALPix order (0..29)- Returns:
- pixel size in steradians
- Examples:
healpixSqdeg(5) = 3.357174580844667
,round(12 * healpixSqdeg(0)) = 41253
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steradiansToSqdeg
public static double steradiansToSqdeg(double sr)
Converts a solid angle from steradians to square degrees.The unit sphere is 4*PI steradians = 360*360/PI square degrees.
- Parameters:
sr
- quantity in steradians- Returns:
- quantity in sqare degrees
- Examples:
round(steradiansToSqdeg(4*PI)) = 41253
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sqdegToSteradians
public static double sqdegToSteradians(double sqdeg)
Converts a solid angle from square degrees to steradians.The unit sphere is 4*PI steradians = 360*360/PI square degrees.
- Parameters:
sqdeg
- quantity in square degrees- Returns:
- quantity in steradians
- Examples:
round(sqdegToSteradians(41253)/PI) = 4
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htmLevel
public static int htmLevel(double pixelsize)
Gives the HTMlevel
parameter suitable for a given pixel size.- Parameters:
pixelsize
- required resolution in degrees- Returns:
- HTM level parameter
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htmResolution
public static double htmResolution(int level)
Gives the approximate resolution in degrees for a given HTM depth level.- Parameters:
level
- HTM depth- Returns:
- approximate angular resolution in degrees
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