Geobee

A standalone PHP library for calculating the great-circle distance between geographical coordinates using a spherical Earth model.

Installation

This library requires no dependencies.

To install it:

• Clone this repository.
• Or use composer: composer require frostybee/geobee

Units of Lengths

The following are the supported units of lengths along with their respective conversion factors:

• m - Meters (default, base unit)
• km - Kilometers (1km = 1000 meters)
• mi - Miles (1mi = 1609.344 meters)
• nm - Nautical miles (1nm = 1852 meters)
• yd - Yards (1yd = 0.9144 meters)
• ft - Feet (1ft = 0.3048 meters)

Note: Unit symbols are case-insensitive (e.g., 'km', 'KM', 'Km' all work).

Usage

Using this library is simple and straightforward. Just instantiate the Calculator class and supply two pairs of latitude/longitude to the calculate() method as shown below.

<?php

use Frostybee\Geobee\Calculator;

/*
 * Calculate the distance from downtown Montreal to Laval.
 * From: Ville-Marie
 *       postal code area: H3A
 *       Latitude/Longitude: 45.4987, -73.5703
 * To: Laval
 *     postal code area: H7T
 *     Latitude/Longitude: 45.5569, -73.7480
 */
$calculator = new Calculator();
$distance = $calculator->calculate(
    45.4987,   // From latitude
    -73.5703,  // From longitude
    45.5569,   // To latitude
    -73.7480   // To longitude
)->getDistance(); // Returns distance in meters (e.g., 15297.83)

Converting the Distance from Meters to other Units

Single Conversion

Use the to() method as show below. However, you must call the calculate() method once before doing any conversions.

use Frostybee\Geobee\Calculator;

$calculator = new Calculator();
$distance = $calculator->calculate(
    45.4987,
    -73.5703,
    45.5569,
    -73.7480
)->to('km'); // Returns distance in kilometers (e.g., 15.298)

You can also specify precision and rounding behavior:

use Frostybee\Geobee\Calculator;

$calculator = new Calculator();
// Syntax: to(unit, decimals, round)
$distance = $calculator->to('mi', 3, false);  // 3 decimals, use floor rounding
$distance = $calculator->to('km', 2);         // 2 decimals, default round (true)

Parameters for to() method:

• $unit (string, required): Unit symbol for conversion
• $decimals (int|null, optional): Number of decimal places (1-9), null for no rounding
• $round (bool, optional, default=true): true = standard rounding, false = floor rounding

Batch Conversions

Convert the distance to multiple units efficiently:

use Frostybee\Geobee\Calculator;

$calculator = new Calculator();
$distance = $calculator->calculate(45.4987, -73.5703, 45.5569, -73.7480);

// Convert to specific units using toMany()
$results = $calculator->toMany(['km', 'mi'], 3, true);
/*
Returns:
array(2) {
  ["km"] => float(15.298)
  ["mi"] => float(9.506)
}
*/

// Convert to all supported units using toAll()
$distance_in_all_units = $calculator->toAll(2, true);
/*
Returns:
array(6) {
  ["m"]  => float(15297.83)
  ["km"] => float(15.30)
  ["ft"] => float(50189.72)
  ["yd"] => float(16729.91)
  ["mi"] => float(9.51)
  ["nm"] => float(8.26)
}
*/

Coordinate Validation

The library provides a public method to validate latitude/longitude coordinates before performing calculations.

Using isCoordinate() Method

use Frostybee\Geobee\Calculator;

$calculator = new Calculator();

// Validate coordinates before calculation
if ($calculator->isCoordinate(45.4987, -73.5703)) {
    $distance = $calculator->calculate(45.4987, -73.5703, 45.5569, -73.7480)
                          ->to('km');
    echo "Distance: $distance km";
} else {
    echo "Invalid coordinates provided.";
}

Coordinate Requirements

• Latitude: Must be between -90 and +90 (decimal degrees)
• Longitude: Must be between -180 and +180 (decimal degrees)
• Both values can have up to 6 decimal places
• Optional +/- sign is allowed
• Arrays are not accepted as coordinate values

Validation Examples

$calculator->isCoordinate(45.4987, -73.5703);   // Valid: true
$calculator->isCoordinate(91, 50);              // Invalid: latitude > 90
$calculator->isCoordinate(45, 181);             // Invalid: longitude > 180
$calculator->isCoordinate("45.5", "-73.7");     // Valid: strings are accepted
$calculator->isCoordinate([45], [73]);          // Invalid: arrays not allowed

Error Handling

The library throws exceptions for invalid input:

• InvalidCoordinateFormatException: When coordinates fail validation
• InvalidUnitException: When an invalid or unsupported unit is specified

use Frostybee\Geobee\Calculator;
use Frostybee\Geobee\InvalidCoordinateFormatException;
use Frostybee\Geobee\InvalidUnitException;

try {
    $calculator = new Calculator();
    $distance = $calculator->calculate(45.4987, -73.5703, 45.5569, -73.7480)
                          ->to('km', 2);
    echo "Distance: $distance km";
} catch (InvalidCoordinateFormatException $e) {
    echo "Invalid coordinates: " . $e->getMessage();
} catch (InvalidUnitException $e) {
    echo "Invalid unit: " . $e->getMessage();
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

Advanced Usage

Method Chaining

The calculate() method returns the Calculator instance, enabling fluent method chaining:

use Frostybee\Geobee\Calculator;


$calculator = new Calculator();
// Chain multiple operations
$km = $calculator->calculate(45.4987, -73.5703, 45.5569, -73.7480)->to('km', 2);
$mi = $calculator->to('mi', 2);  // Reuse the same calculation
$nm = $calculator->to('nm', 2);

Edge Cases

Zero Distance (Same Coordinates)

When calculating distance from a point to itself:

use Frostybee\Geobee\Calculator;

$calculator = new Calculator();
$distance = $calculator->calculate(45.5, -73.7, 45.5, -73.7)->getDistance();
// Returns: 0

$km = $calculator->to('km');
// Returns: 0

$all = $calculator->toAll();
// Returns: [] (empty array)

Note: toAll() returns an empty array when distance is zero, while to() returns 0.

Precision Control

Control the precision of converted distances:

use Frostybee\Geobee\Calculator;

$calculator = new Calculator();
$calculator->calculate(45.4987, -73.5703, 45.5569, -73.7480);

// No rounding (returns full precision)
$distance = $calculator->to('km');  // e.g., 15.29783...

// With decimals (1-9 allowed)
$distance = $calculator->to('km', 2);      // e.g., 15.30
$distance = $calculator->to('km', 5);      // e.g., 15.29783

// Rounding behavior
$distance = $calculator->to('km', 2, true);   // Standard rounding (PHP_ROUND_HALF_UP)
$distance = $calculator->to('km', 2, false);  // Floor rounding (PHP_ROUND_HALF_DOWN)

API Reference

Calculator Class Methods

Method	Parameters	Return Type	Description
calculate()	float $from_lat, float $from_lon, float $to_lat, float $to_lon	self	Calculates distance between two coordinates. Returns $this for chaining.
getDistance()	None	float	Returns the calculated distance in meters.
to()	string $unit, ?int $decimals = null, bool $round = true	float|int	Converts distance to specified unit.
toMany()	array $units = [], ?int $decimals = null, bool $round = true	array	Converts distance to multiple units. Returns associative array.
toAll()	?int $decimals = null, bool $round = true	array	Converts distance to all supported units. Returns associative array.
isCoordinate()	mixed $latitude, mixed $longitude	bool	Validates a coordinate pair. Returns true if valid.

Implementation Details

• Algorithm: Great-circle distance using spherical Earth model (numerically stable implementation with atan2())
• Earth Radius: 6,378,137 meters (WGS84 semi-major axis)
• Coordinate Format: Decimal degrees with up to 6 decimal places
• Precision: Suitable for most geographic distance calculations; for higher precision on an ellipsoidal model, consider using a full geodesic library

License

Geobee is an open-source library licensed under the MIT LICENSE.