Package cds.healpix
Interface AuxiliaryAxis
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 given
The resolution at a given
If we want to represent temporal data, we can represent:
Example: depth 12 => NSIDE = 4096 => angular resolution = 51.5 arcsec => 4096 / 365 = 11.222 years with a resolution = 1 day
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 given
depth
, the [0.0, 1.0[ interval is divided into NSIDE
(=2^depth) segments.The resolution at a given
depth
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
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Method Details
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name
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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