Places

use geo.qweruse distance_km, bounding_box from geo      // Quillo 0.6: only these

geohash = "0.13"

// Shops near a visitor, nearest first.////   quillo run geo.qwe      then open http://localhost:8080/near?lat=52.37&lon=4.89use "geo.qwer"let shops = [    { name: "Centraal", lat: 52.3791, lon: 4.9003 },    { name: "Zuid", lat: 52.3389, lon: 4.8723 },    { name: "Utrecht", lat: 52.0907, lon: 5.1214 },]route GET /near ? { lat: float, lon: float } {    let box = bounding_box(lat, lon, 10.0)    shops        | filter((s) => s.lat >= box.min_lat && s.lat <= box.max_lat && s.lon >= box.min_lon && s.lon <= box.max_lon)        | map((s) => { name: s.name, km: round(distance_km(lat, lon, s.lat, s.lon), 2), cell: geohash_encode(s.lat, s.lon, 6)? })        | sort_by((s) => s.km)}

//! Places: distances on the globe, bounding boxes for "near me" queries in SQL, and geohashes for grouping points.//! version: 1.0.0//!//! [dependencies]//! geohash = "0.13"use serde_json::{json, Value};const EARTH_KM: f64 = 6371.0088;/// How far apart two points are, in kilometres, along the globe (haversine).pub fn distance_km(lat1: f64, lon1: f64, lat2: f64, lon2: f64) -> f64 {    let (p1, p2) = (lat1.to_radians(), lat2.to_radians());    let (dp, dl) = ((lat2 - lat1).to_radians(), (lon2 - lon1).to_radians());    let a = (dp / 2.0).sin().powi(2) + p1.cos() * p2.cos() * (dl / 2.0).sin().powi(2);    2.0 * EARTH_KM * a.sqrt().asin()}/// `{ min_lat, max_lat, min_lon, max_lon }` around a point: `where lat between ? and ? and lon between ? and ?` finds the candidates, `distance_km` the exact ones.pub fn bounding_box(lat: f64, lon: f64, radius_km: f64) -> Value {    let dlat = (radius_km / EARTH_KM).to_degrees();    let dlon = (radius_km / (EARTH_KM * lat.to_radians().cos().abs().max(1e-6))).to_degrees();    json!({ "min_lat": (lat - dlat).max(-90.0), "max_lat": (lat + dlat).min(90.0), "min_lon": (lon - dlon).max(-180.0), "max_lon": (lon + dlon).min(180.0) })}/// The geohash of a point, `precision` characters long (5 is about 5 km, 7 about 150 m).pub fn geohash_encode(lat: f64, lon: f64, precision: i64) -> Result<String, String> {    geohash::encode(geohash::Coord { x: lon, y: lat }, precision.clamp(1, 12) as usize).map_err(|e| e.to_string())}/// The centre of a geohash's cell: `{ lat, lon }`.pub fn geohash_decode(hash: &str) -> Result<Value, String> {    let (c, _, _) = geohash::decode(hash).map_err(|e| e.to_string())?;    Ok(json!({ "lat": c.y, "lon": c.x }))}/// The eight cells around a geohash's, to search a cell and its neighbours.pub fn geohash_neighbors(hash: &str) -> Result<Vec<String>, String> {    let n = geohash::neighbors(hash).map_err(|e| e.to_string())?;    Ok(vec![n.n, n.ne, n.e, n.se, n.s, n.sw, n.w, n.nw])}