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The Qbox is a method for splitting the sky into a hierarchical
environment CDS , Simbad, VizieR
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The dichotomic procedure uses the projections (X,Y) of the directions on the 6 faces of a cube numbered 1 (z=1), 2 (y=1), 3 (x=1), 4 (x=-1), 5 (y=-1) and 6 (z=-1).
Each cube face is then divided into 4 areas; each area is further divided into four pieces, etc. The number of valid qboxes is
Level Lower # qboxes qbox_size
0 9 6 83°
1 36 24 41°
2 144 96 20°
3 576 384 10°
4 2304 1536 5°
5 9216 6144 2°30'
6 36864 24576 1°15'
7 147456 98304 40'
8 589824 393216 20'
9 2359296 1572864 10'
10 9437184 6291456 5'
11 37748736 25165824 2'30"
12 150994944 100663296 1'15"
where level is a number which can be changed at any time using
setLevel(level) method.
The present implementation assumes that level<=12, corresponding to a maximum of 28 bits in the qbox number.
For a level 6, the qbox number is a short integer with bits (from left to right) 1ppp xyxy xyxy xyxy. The leftmost `1' bit allows the recognition of the level; bits p represent the face number (1 to 6), x and y the position, expressed with level bits, along the axises defined above for the face; going one level down in the hierarchy is therefore just a shift of 2 bits and updating the 2 rightmost bits.
The selection of valid qboxes makes usage of an Enumeration which returns the valid qboxes via its nextElement method.
| Field Summary | |
static boolean |
DEBUG
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static int |
QBOX_ANY
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static int |
QBOX_NONE
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static int |
QBOX_SOME
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| Method Summary | |
int |
checkTarget(int qbox)
Checking the condition -- returns QBOX_NONE QBOX_ANY QBOX_SOME |
| Field Detail |
public static final int QBOX_NONE
public static final int QBOX_ANY
public static final int QBOX_SOME
public static final boolean DEBUG
| Method Detail |
public int checkTarget(int qbox)
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