flutter_geo_hash 0.0.7

flutter_geo_hash: ^0.0.7 copied to clipboard

example/example.dart

import 'package:flutter_geo_hash/flutter_geo_hash.dart';

void main() {
  final geoHash = GeoHashUtils();

  // 1. Compute the geohash to store alongside each location.
  const places = {
    'Buckingham Palace': GeoHashPoint(51.5014, -0.1419),
    'Windsor Castle': GeoHashPoint(51.4839, -0.6044),
    'Brighton Pier': GeoHashPoint(50.8169, -0.1367),
    'Cambridge': GeoHashPoint(52.2053, 0.1218),
  };
  final geohashes = {
    for (final MapEntry(key: name, value: location) in places.entries)
      name: geoHash.geoHashForLocation(location),
  };
  print('Stored geohashes:');
  geohashes.forEach((name, hash) => print('  $name: $hash'));

  // 2. Compute the geohash ranges covering 50 km around central London.
  const center = GeoHashPoint(51.5074, -0.1278);
  const radiusInM = 50 * 1000.0;
  final bounds = geoHash.geohashQueryBounds(center, radiusInM);
  print('Ranges to query:');
  for (final range in bounds) {
    print('  from ${range[0]} to ${range[1]}');
  }

  // 3. A database query returns every place whose geohash is in a range.
  // Ranges are rectangles, so discard the places outside the circle.
  print('Query results:');
  for (final MapEntry(key: name, value: hash) in geohashes.entries) {
    final matched = bounds.any((range) =>
        hash.compareTo(range[0]) >= 0 && hash.compareTo(range[1]) <= 0);
    if (!matched) {
      continue;
    }
    final location = places[name]!;
    final kilometers = geoHash.distanceBetween(center, location);
    final verdict = geoHash.isWithinRadius(center, location, radiusInM)
        ? 'within 50 km'
        : 'false positive, discarded';
    print('  $name: ${kilometers.toStringAsFixed(1)} km, $verdict');
  }

  // 4. Decode a geohash and list the cells around it.
  final cell = geohashes['Buckingham Palace']!.substring(0, 6);
  print('Cell $cell:');
  print('  bounds: ${geoHash.decodeGeoHashBounds(cell)}');
  print('  center: ${geoHash.decodeGeoHash(cell)}');
  geoHash.geoHashNeighbors(cell).forEach((direction, neighbor) {
    print('  ${direction.name} neighbor: $neighbor');
  });
}