Function geohash_encode

nodedb-spatial/src/geohash.rs:47–97

Encode a (longitude, latitude) coordinate to a geohash string. - `precision`: number of characters (1–12). Default 6 gives ~1.2 km cells. - Longitude range: [-180, 180] - Latitude range: [-90, 90] Returns an empty string if precision is 0.

(lng: f64, lat: f64, precision: u8)

///
/// Returns an empty string if precision is 0.
pub fn geohash_encode(lng: f64, lat: f64, precision: u8) -> String {
    let precision = precision.min(12) as usize;
    if precision == 0 {
        return String::new();
    }

    let mut min_lng = -180.0_f64;
    let mut max_lng = 180.0_f64;
    let mut min_lat = -90.0_f64;
    let mut max_lat = 90.0_f64;

    let mut result = String::with_capacity(precision);
    let mut bits: u8 = 0;
    let mut bit_count: u8 = 0;
    let mut is_lng = true; // Longitude first (even bits).

    // Each character encodes 5 bits. Total bits = precision * 5.
    let total_bits = precision * 5;

    for _ in 0..total_bits {
        if is_lng {
            let mid = (min_lng + max_lng) / 2.0;
            if lng >= mid {
                bits = (bits << 1) | 1;
                min_lng = mid;
            } else {
                bits <<= 1;
                max_lng = mid;
            }
        } else {
            let mid = (min_lat + max_lat) / 2.0;
            if lat >= mid {
                bits = (bits << 1) | 1;
                min_lat = mid;
            } else {
                bits <<= 1;
                max_lat = mid;
            }
        }
        is_lng = !is_lng;
        bit_count += 1;

        if bit_count == 5 {
            result.push(BASE32[bits as usize] as char);
            bits = 0;
            bit_count = 0;
        }
    }

    result
}

/// Decode a geohash string to its bounding box.
///