rapidgeo-distance

Geographic and planar distance calculations.

All coordinates use longitude, latitude ordering (lng, lat).

Installation

[dependencies]
rapidgeo-distance = "0.1"

# Or with optional features
rapidgeo-distance = { version = "0.1", features = ["batch", "vincenty"] }

Quick Start

use rapidgeo_distance::{LngLat, geodesic, euclid};

let sf = LngLat::new_deg(-122.4194, 37.7749);   // San Francisco
let nyc = LngLat::new_deg(-74.0060, 40.7128);   // New York City

// Haversine: ±0.5% accuracy for distances <1000km
let distance = geodesic::haversine(sf, nyc);
println!("Distance: {:.1} km", distance / 1000.0);

// Vincenty: Sub-meter accuracy globally (requires "vincenty" feature)
let precise = geodesic::vincenty_distance_m(sf, nyc)?;
println!("Precise: {:.3} km", precise / 1000.0);

// Euclidean: Fast but inaccurate for large distances
let euclidean = euclid::distance_euclid(sf, nyc);
println!("Euclidean: {:.6}°", euclidean);

What This Crate Does

This crate calculates distances between geographic coordinates using three approaches:

1. Geodesic algorithms - Account for Earth's shape (haversine, Vincenty)
2. Euclidean distance - Treats coordinates as flat plane points
3. Batch operations - Process many points efficiently with optional parallelization

All geodesic calculations use the WGS84 ellipsoid.

API Overview

Core Types

// All functions work with LngLat coordinates
let point = LngLat::new_deg(longitude, latitude);
let (lng_rad, lat_rad) = point.to_radians();

Coordinate Format Detection

The crate automatically detects and converts coordinate data from various formats (tuples, flat arrays, GeoJSON) to the internal LngLat representation:

use rapidgeo_distance::formats::{coords_to_lnglat_vec, CoordinateInput};

// Automatically detects lng,lat vs lat,lng ordering
let coords = vec![
    (37.7749, -122.4194),  // Latitude,longitude format (detected)
    (40.7128, -74.0060),   // Automatically corrected to lng,lat
];

let input = CoordinateInput::Tuples(coords);
let lnglat_coords = coords_to_lnglat_vec(&input);

See Coordinate Format Documentation for detailed examples of supported formats.

Geodesic Distances (Earth-Aware)

use rapidgeo_distance::geodesic::{haversine, vincenty_distance_m, VincentyError};

// Haversine: Fast, good accuracy for distances <1000km
let distance_m = haversine(point1, point2);

// Vincenty: Slower, very accurate, may fail for antipodal points
match vincenty_distance_m(point1, point2) {
    Ok(distance) => println!("{:.3} m", distance),
    Err(VincentyError::DidNotConverge) => {
        // Use haversine as fallback
        let fallback = haversine(point1, point2);
    }
    Err(VincentyError::Domain) => {
        // Invalid coordinates (NaN/infinite)
    }
}

Euclidean Distances (Flat Plane)

use rapidgeo_distance::euclid::{distance_euclid, distance_squared, point_to_segment};

// Basic distance in degrees (not meters)
let dist_deg = distance_euclid(point1, point2);

// Squared distance (avoids sqrt for performance)
let dist_sq = distance_squared(point1, point2);

// Point to line segment distance
let segment = (point1, point2);
let distance = point_to_segment(test_point, segment);

Point-to-Segment Distances

use rapidgeo_distance::geodesic::{point_to_segment_enu_m, great_circle_point_to_seg};

let segment = (start_point, end_point);

// ENU projection (good for small areas)
let distance = point_to_segment_enu_m(point, segment);

// Great circle method (accurate but slower)
let distance = great_circle_point_to_seg(point, segment);

Batch Operations

use rapidgeo_distance::batch::{
    pairwise_haversine, path_length_haversine,
    pairwise_haversine_into, distances_to_point_into
};

let path = vec![point1, point2, point3];

// Process consecutive pairs
let distances: Vec<f64> = pairwise_haversine(&path).collect();

// Total path length
let total = path_length_haversine(&path);

// Write to pre-allocated buffer (no allocation)
let mut buffer = vec![0.0; path.len() - 1];
pairwise_haversine_into(&path, &mut buffer);

Parallel Processing (requires "batch" feature)

#[cfg(feature = "batch")]
use rapidgeo_distance::batch::{
    pairwise_haversine_par, path_length_haversine_par,
    distances_to_point_par
};

let large_dataset = load_many_points();

// Parallel processing (beneficial for >1000 points)
let distances = pairwise_haversine_par(&large_dataset);
let total = path_length_haversine_par(&large_dataset);

Algorithm Selection

Accuracy Details

Haversine: Uses spherical approximation with ellipsoidal correction for the WGS84 ellipsoid. Good tradeoff for accuracy vs speed.

Vincenty: Implements Vincenty's inverse formula on WGS84 ellipsoid. May fail to converge for nearly antipodal points.

Euclidean: Simple Pythagorean theorem in degree space. Ignores Earth curvature. Error increases with distance and latitude.

Features

• Default: Haversine and Euclidean functions
• vincenty: Enables high-precision Vincenty calculations
• batch: Enables Rayon-based parallel processing

Performance Notes

Serial vs Parallel: Parallel functions are faster for large datasets (>1000 points) but have overhead. Use serial for small datasets.

Memory Allocation: Functions ending in _into write to pre-allocated buffers, avoiding allocation overhead.

Benchmarks: On Intel i9-10900F:

• Euclidean: ~1ns per calculation
• Haversine: ~46ns per calculation
• Vincenty: ~271ns per calculation
• Pre-allocated buffers: ~60% faster than allocating

Coordinate System

All coordinates use longitude, latitude ordering:

• Longitude: -180.0 to +180.0° (West to East)
• Latitude: -90.0 to +90.0° (South to North)

let coord = LngLat::new_deg(lng, lat);  // Note: lng first

Limitations

• Vincenty may fail for nearly antipodal points
• Euclidean accuracy degrades significantly with distance and latitude
• Parallel functions require the batch feature
• All geodesic calculations assume WGS84 ellipsoid
• Point-to-segment functions assume segments shorter than hemisphere

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT License (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.