Engineer at Mapbox, creator of Leaflet, algorithms geek, open source enthusiast, musician, father of twin girls, Ukrainian. 🇺🇦
Published
Edited
Jun 18, 2020
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Importers
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coords = { // decode Morton indices into 3D coords
const coords = [];
for (const c of mortonIndices) {
const x = compact1By2(c >> 0);
const y = compact1By2(c >> 1);
const z = compact1By2(c >> 2);
coords.push({x, y, z});
}
return coords;
}
// convert [0, 1, 2, ...] sequence of Hilbert values into Morton indices
mortonIndices = new Uint32Array(side ** 3).map((v, i) => transformCurve(i, order, hilbertToMortonTable))
// convert a Hilbert value into a Morton index using a lookup table
transformCurve = (index, bits, lookupTable) => {
let out = 0;
for (let i = 3 * (bits - 1), transform = 0; i >= 0; i -= 3) {
transform = lookupTable[transform | ((index >> i) & 7)];
out = (out << 3) | (transform & 7);
transform &= ~7;
}
return out;
}
// lookup table for converting a Hilbert value to a Morton index
hilbertToMortonTable = Uint8Array.of(
48, 33, 35, 26, 30, 79, 77, 44,
78, 68, 64, 50, 51, 25, 29, 63,
27, 87, 86, 74, 72, 52, 53, 89,
83, 18, 16, 1, 5, 60, 62, 15,
0, 52, 53, 57, 59, 87, 86, 66,
61, 95, 91, 81, 80, 2, 6, 76,
32, 2, 6, 12, 13, 95, 91, 17,
93, 41, 40, 36, 38, 10, 11, 31,
14, 79, 77, 92, 88, 33, 35, 82,
70, 10, 11, 23, 21, 41, 40, 4,
19, 25, 29, 47, 46, 68, 64, 34,
45, 60, 62, 71, 67, 18, 16, 49
)
// extract every 3rd bit from a number to decode a component of a Morton index
compact1By2 = (x) => { // https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/
x &= 0x09249249;
x = (x ^ (x >> 2)) & 0x030c30c3;
x = (x ^ (x >> 4)) & 0x0300f00f;
x = (x ^ (x >> 8)) & 0xff0000ff;
x = (x ^ (x >> 16)) & 0x000003ff;
return x;
}
Zdog = require('zdog')
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