Google Maps Utils for Dart/Flutter

A faithful Dart port of the core geometry classes from Google's android-maps-utils library.

✨ Features

All calculations use the same spherical algorithms as the original Android Java/Kotlin library — results are identical.

🚀 Getting Started

Installation

Add to your pubspec.yaml:

dependencies:
  google_maps_utils: ^5.0.0

Then run:

dart pub get

Import

import 'package:google_maps_utils/google_maps_utils.dart';

Quick Start

Use the GoogleMapsUtils class as the unified namespace for all operations:

// Spherical geometry
final distance = GoogleMapsUtils.spherical.computeDistanceBetween(from, to);
final heading = GoogleMapsUtils.spherical.computeHeading(from, to);

// Polyline utilities
final path = GoogleMapsUtils.poly.decode(encodedString);
final simplified = GoogleMapsUtils.poly.simplify(path, 5000.0);

// Math helpers
final wrapped = GoogleMapsUtils.math.wrap(190.0, -180.0, 180.0); // -170.0

// Bounding boxes return a lightweight record: (ne: Point, sw: Point)
final bounds = GoogleMapsUtils.spherical.toBounds(-23.55, -46.63, 1000.0);
print(bounds.ne); // north-east corner
print(bounds.sw); // south-west corner

📖 Usage

Distance Between Two Points

final from = Point<double>(0.0, 0.0);
final to = Point<double>(10.0, 5.0);

final distance = GoogleMapsUtils.spherical.computeDistanceBetween(from, to);
// 1241932.5985192063 meters

Heading (Bearing)

final heading = GoogleMapsUtils.spherical.computeHeading(from, to);
// 26.302486345342523 degrees (clockwise from North)

Angle Between Points

final angle = GoogleMapsUtils.spherical.computeAngleBetween(from, to);
// 0.19493500057547358 radians (unit-sphere arc distance)

Compute Offset (Move a Point)

// Move 1000 meters east (heading 90°) from the origin
final origin = Point<double>(0.0, 0.0);
final destination = GoogleMapsUtils.spherical.computeOffset(origin, 1000.0, 90.0);
// Returns the Point at the new location

Compute Offset Origin (Reverse Lookup)

// Given a destination, distance, and heading — find where you started
final origin = GoogleMapsUtils.spherical.computeOffsetOrigin(destination, 1000.0, 90.0);
// Returns Point? (null if no solution exists)

Interpolation (SLERP)

// Find the point 25% of the way between two locations
final quarter = GoogleMapsUtils.spherical.interpolate(from, to, 0.25);

Path Length

final path = <Point<double>>[
  Point(0.0, 0.0),
  Point(1.0, 1.0),
  Point(2.0, 0.0),
];

final length = GoogleMapsUtils.spherical.computeLength(path);
// Total distance in meters along the path

Compass Cardinal Direction

final cardinal = GoogleMapsUtils.spherical.getCardinal(45.0);
// 'NE'

final cardinal2 = GoogleMapsUtils.spherical.getCardinal(200.0);
// 'SSW'

Polyline Decoding

// Decode a Google Encoded Polyline string into coordinates
final path = GoogleMapsUtils.poly.decode(
    'wjiaFz`hgQs}GmmBok@}vX|cOzKvvT`uNutJz|UgqAglAjr@ijBz]opA');
// Returns List<Point<double>> with 17 points

Polyline Encoding

// Encode coordinates back to a compact string
final encoded = GoogleMapsUtils.poly.encode(path);

Douglas-Peucker Simplification

// Reduce points while preserving shape (tolerance in meters)
final simplified = GoogleMapsUtils.poly.simplify(path, 5000.0);
// 17 points → 6 points

Point-in-Polygon

final point = Point<double>(-31.623060, -60.686690);

final polygon = <Point<double>>[
  Point(-31.624115, -60.688734),
  Point(-31.624115, -60.684657),
  Point(-31.621594, -60.686717),
  Point(-31.624115, -60.688734),
];

final isInside = GoogleMapsUtils.poly.containsLocationPoly(point, polygon);
// true

// Also supports geodesic (great-circle) edges:
final isInsideGeodesic = GoogleMapsUtils.poly.containsLocationPoly(
  point, polygon, geodesic: true,
);

Point-on-Path Detection

final route = <Point<double>>[
  Point(0.0, 0.0),
  Point(0.0, 10.0),
];

// Is the point on or near the polyline? (default tolerance: 0.1m)
final isOnPath = GoogleMapsUtils.poly.isLocationOnPath(
  Point(0.0, 5.0), route, true, // geodesic
);
// true

// Get which segment the point falls on
final segmentIndex = GoogleMapsUtils.poly.locationIndexOnPath(
  Point(0.0, 5.0), route, true,
);
// 0 (between route[0] and route[1])

Point-on-Edge (Polygon Boundary)

final square = <Point<double>>[
  Point(0.0, 0.0),
  Point(0.0, 10.0),
  Point(10.0, 10.0),
  Point(10.0, 0.0),
];

// Includes the closing segment (last→first)
final isOnEdge = GoogleMapsUtils.poly.isLocationOnEdge(
  Point(5.0, 0.0), square, true,
);
// true

Distance to a Line Segment

final p = Point<double>(-23.54545, -23.898098);
final start = Point<double>(0.0, 0.0);
final end = Point<double>(10.0, 5.0);

final dist = GoogleMapsUtils.poly.distanceToLine(p, start, end);
// 3675538.019968191 meters

Compute Area

final area = GoogleMapsUtils.spherical.computeArea(polygon);
// Area in square meters

final signedArea = GoogleMapsUtils.spherical.computeSignedArea(polygon);
// Positive = counter-clockwise, negative = clockwise

Bounding Boxes

// Create bounds from a center point + radius
// Returns a LatLngBounds record: (ne: Point<double>, sw: Point<double>)
final bounds = GoogleMapsUtils.spherical.toBounds(-23.55, -46.63, 1000.0);
print(bounds.ne); // north-east corner
print(bounds.sw); // south-west corner

// Create bounds from a list of points
final bounds = GoogleMapsUtils.spherical.toBoundsFromPoints(path);

// Get the center of a bounds
final center = GoogleMapsUtils.spherical.centerFromLatLngBounds(bounds);

// Split bounds into a grid (division² sub-bounds)
final tiles = GoogleMapsUtils.spherical.toSubBounds(bounds, division: 3);
// Returns 9 sub-bounds

Closed Polygon Check

GoogleMapsUtils.poly.isClosedPolygon(polygon); // true if first == last point

Custom Tolerance (On-Path / On-Edge)

// Default tolerance is 0.1 meters. Use custom tolerance for proximity:
final isNear = GoogleMapsUtils.poly.isLocationOnPathTolerance(
  point, polyline, true, 50.0, // 50 meters tolerance
);

// Same for edges:
final isNearEdge = GoogleMapsUtils.poly.isLocationOnEdgeTolerance(
  point, polygon, true, 50.0,
);

// With index:
final idx = GoogleMapsUtils.poly.locationIndexOnPathTolerance(
  point, polyline, true, 50.0,
);

Math Helpers (Low-Level)

// Clamp a value to a range
GoogleMapsUtils.math.clamp(15.0, 0.0, 10.0); // 10.0

// Wrap a value into [min, max) — useful for longitude
GoogleMapsUtils.math.wrap(190.0, -180.0, 180.0); // -170.0

// Non-negative modulo
GoogleMapsUtils.math.mod(-1.0, 360.0); // 359.0

// Mercator projection (radians)
final y = GoogleMapsUtils.math.mercator(latInRadians);
final lat = GoogleMapsUtils.math.inverseMercator(y);

// Haversine / inverse haversine
final h = GoogleMapsUtils.math.hav(angleInRadians);
final angle = GoogleMapsUtils.math.arcHav(h);

// Haversine distance on unit sphere
final havDist = GoogleMapsUtils.math.havDistance(lat1, lat2, dLng);

Degree / Radian Conversions

GoogleMapsUtils.spherical.toRadians(90.0);  // 1.5707963... (π/2)
GoogleMapsUtils.spherical.toDegrees(pi);    // 180.0

📋 Full Example

See example/example.dart for a complete runnable demo covering all features.

Heading: 26.302486345342523 degrees
Angle: 0.19493500057547358 radians
Distance to Line: 3675538.019968191 meters
path size length: 17
simplified path: wjiaFz`hgQcjIke\t{d@|aOutJz|UokC}xWomJdjM
path size simplified length: 6
Distance: 1241932.5985192063 meters
Distance: 1066.7243813716539 meters of polygon
point is inside polygon?: true

📐 API Reference

GoogleMapsUtils.spherical

GoogleMapsUtils.poly

GoogleMapsUtils.math

📊 Status

3 of 78 classes from android-maps-utils have been converted — these are the most widely used. Need another class? Open an issue and I'll prioritize it.

💚 Sponsor

This package is proudly sponsored by bus2.me.

If this package saves you time, consider supporting its development.

🔗 Links

• 📦 pub.dev package
• 📖 API documentation
• 🐛 Issue tracker
• 🤖 android-maps-utils (upstream)
• 💬 Stack Overflow
• 🦋 Flutter community request

🤝 Contributing

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Make your changes with tests
4. Ensure dart analyze --fatal-infos and dart test pass
5. Open a Pull Request

📄 License

This project is licensed under the Apache License 2.0 — see the LICENSE file for details.

Original Java source: Copyright 2008, 2013 Google Inc.