Package cds.healpix
Interface AuxiliaryAxis
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public interface AuxiliaryAxis
Define an auxiliary axis, i.e. a 3rd dimension to be taken into account when computing an HEALPix index.
To compute a hash using the auxiliary axis, the values must be projected along the z-axis ranging from 0 (inclusive) to 1 (exclusive).
The maximum depth when using an auxiliary axis is 19 (4 + 19 * 3 = 61 bits). So the maximum number of intervals is 2^19 = 524288.
At a givendepth
, the [0.0, 1.0[ interval is divided intoNSIDE
(=2^depth) segments.
The resolution at a givendepth
is thus abs(unproject(1) - unproject(0)) /NSIDE
.
If we want to represent temporal data, we can represent:- about 1 years with intervals being time ranges of 1 min;
- 60.68 years with intervals being time ranges of 1 hour.
Example: depth 12 => NSIDE = 4096 => angular resolution = 51.5 arcsec => 4096 / 365 = 11.222 years with a resolution = 1 day- Author:
- F.-X. Pineau
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description java.lang.String
name()
Returns the name of the auxiliary axis.double
project(double x)
Project (or normalize) the given auxiliary axis value into the [0.0, 1.0[ range.double
unproject(double y)
Unproject (denormalize) the value from the [0.0, 1.0[ range.
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Method Detail
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name
java.lang.String name()
Returns the name of the auxiliary axis.- Returns:
- the name of the auxiliary axis.
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project
double project(double x)
Project (or normalize) the given auxiliary axis value into the [0.0, 1.0[ range.- Parameters:
x
- the auxiliary axis value to be projected (normalized).- Returns:
- the projected (normalized) value on the auxiliary axis, in [0.0, 1.0[.
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unproject
double unproject(double y)
Unproject (denormalize) the value from the [0.0, 1.0[ range.- Parameters:
y
- the projected (normalized) value on the auxiliary axis, in [0.0, 1.0[- Returns:
- the unprojected (denormalize) value on the auxiliary axis.
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