geonumber/lib/index.js

Library for encoding geographic coordinates as single number with any number of bits

export function encodeNumber(value, bits) {
    const cleanBits = BigInt(bits);
    const max = Number(1n << cleanBits);
    return BigInt(Math.round(value * max));
}
export function decodeNumber(encoded, bits) {
    const cleanBits = BigInt(bits);
    const max = Number(1n << cleanBits);
    return Number(encoded) / max;
}
export function merge(a, b, bits) {
    const cleanBits = BigInt(bits);
    let result = 0n;
    const oddBits = cleanBits & 1n;
    for (let dstBit = 0n; dstBit < cleanBits; dstBit++) {
        const srcBit = dstBit >> 1n;
        result |= (((((dstBit & 1n) != oddBits) ? a : b) >> srcBit) & 1n) << dstBit;
    }
    return result;
}
export function split(encoded, bits) {
    const cleanBits = BigInt(bits);
    let a = 0n;
    let b = 0n;
    const oddBits = cleanBits & 1n;
    for (let srcBit = 0n; srcBit < cleanBits; srcBit++) {
        const dstBit = srcBit >> 1n;
        if ((srcBit & 1n) == oddBits) {
            b |= ((encoded >> srcBit) & 1n) << dstBit;
        }
        else {
            a |= ((encoded >> srcBit) & 1n) << dstBit;
        }
    }
    return [a, b];
}
export function encodeLocation({ lat, lon }, bits) {
    const cleanBits = BigInt(bits);
    const latBits = cleanBits >> 1n;
    const lonBits = cleanBits - latBits;
    const normalizedLat = (lat + 90) / 180;
    const normalizedLon = (lon + 180) / 360;
    const clearedLat = normalizedLat - Math.floor(normalizedLat);
    const clearedLon = normalizedLon - Math.floor(normalizedLon);
    const encodedLat = encodeNumber(clearedLat, latBits);
    const encodedLon = encodeNumber(clearedLon, lonBits);
    const merged = merge(encodedLon, encodedLat, cleanBits);
    return merged;
}
export function decodeLocation(number, bits) {
    const cleanNumber = BigInt(number);
    const cleanBits = BigInt(bits);
    const latBits = cleanBits >> 1n;
    const lonBits = cleanBits - latBits;
    const [encodedLon, encodedLat] = split(cleanNumber, cleanBits);
    const normalizedLat = decodeNumber(encodedLat, latBits);
    const normalizedLon = decodeNumber(encodedLon, lonBits);
    const lat = normalizedLat * 180 - 90;
    const lon = normalizedLon * 360 - 180;
    return { lat, lon };
}
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