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https://issues.apache.org/jira/browse/LUCENE-6480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14543396#comment-14543396
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Karl Wright commented on LUCENE-6480:
-------------------------------------
Here are (untested) code snippets for converting a single double value to a
long and back, such that locality is preserved etc. In order to use these with
x,y,z you would need to use a modified three-part Morton encoding (similar to
what was done for GeoPointField) to interleave the bits resulting from the
encoding method, and the reverse operation to de-convolve the long into three
sets of bits.
{code}
public static long toGeoBits(double value) {
// Get the bits for the value
long lvalue = Double.doubleToLongBits(value);
// The exponent will range from 0 to -1023. Use it to compute the
// amount to shift the mantissa. But shift left one first, so we
sign-extend properly.
int exponent = (int)((lvalue << 1) >> 53);
// Shift the mantissa to the leftmost position and add the hidden bit
long mantissa = (lvalue & 0x000FFFFFFFFFFFFFL) << 11;
// Special value of zero occurs when exponent == 0 and mantissa == 0. But
a rigorous interpretation
// of this value is 2^(-1023), which is close enough to zero for our work,
so we do nothing special.
long fullMantissa = mantissa | 0x8000000000000000L;
// Now, compute the amount to shift the mantissa. We want the mantissa,
// plus the hidden bit, to wind up in the right place. This will allow
room for the sign bit too
return (mantissa >>> (1024-exponent)) | ((lvalue & 0x8000000000000000L) ^
0x8000000000000000L);
}
protected final static double SHIFT_RIGHT_AMT =
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 *
0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 * 0.5;
public static double fromGeoBits(long bits) {
// To compute the exponent, we need to count the number of "0" bits from
the next-to-highest position down to
// the first "1". This is not trivial to do without a loop, which would
slow us down. So a better
// way to do the job is to just cast from the long to a double, and extract
the exponent from
// the result.
double castedDouble = (double)(bits & 0x7FFFFFFFFFFFFFFFL);
// We need to divide by 2^63 to get the number back in range, and set the
appropriate sign.
castedDouble *= SHIFT_RIGHT_AMT;
if ((bits & 0x8000000000000000L) == 0)
return -castedDouble;
return castedDouble;
}
{code}
> Extend Simple GeoPointField Type to 3d
> ---------------------------------------
>
> Key: LUCENE-6480
> URL: https://issues.apache.org/jira/browse/LUCENE-6480
> Project: Lucene - Core
> Issue Type: New Feature
> Components: core/index
> Reporter: Nicholas Knize
>
> [LUCENE-6450 | https://issues.apache.org/jira/browse/LUCENE-6450] proposes a
> simple GeoPointField type to lucene core. This field uses 64bit encoding of 2
> dimensional points to construct sorted term representations of GeoPoints
> (aka: GeoHashing).
> This feature investigates adding support for encoding 3 dimensional
> GeoPoints, either by extending GeoPointField to a Geo3DPointField or adding
> an additional 3d constructor.
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