Repository: jftuga/geodist
Branch: main
Commit: 3d2621e37888
Files: 10
Total size: 12.3 KB

Directory structure:
gitextract_1ubr643k/

├── .gitignore
├── LICENSE
├── README.md
├── example/
│   └── example.go
├── go.mod
├── haversine.go
├── haversine_test.go
├── shared.go
├── vincenty.go
└── vincenty_test.go

================================================
FILE CONTENTS
================================================

================================================
FILE: .gitignore
================================================
# Binaries for programs and plugins
*.exe
*.exe~
*.dll
*.so
*.dylib

# Test binary, built with `go test -c`
*.test

# Output of the go coverage tool, specifically when used with LiteIDE
*.out

# Dependency directories (remove the comment below to include it)
# vendor/
.idea/


================================================
FILE: LICENSE
================================================
MIT License

Copyright (c) 2021 John Taylor

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


================================================
FILE: README.md
================================================
# geodist
GoLang package to compute the distance between two geographic latitude, longitude coordinates

## Algorithm Comparison
* `Vincenty` is more accurate than `Haversine` because is considers the Earth's [ellipticity](https://www.dictionary.com/browse/ellipticity) when performing the calculation, but takes a longer time to compute.
* [Wikipedia: Haversine](https://en.wikipedia.org/wiki/Haversine_formula)
* [Wikipedia: Vincenty](https://en.wikipedia.org/wiki/Vincenty%27s_formulae)
* [Is the Haversine Formula or the Vincenty's Formula better for calculating distance?](https://stackoverflow.com/q/38248046/452281)

## Example
* [example.go](example/example.go)

```go
	var newYork = geodist.Coord{Lat: 40.7128, Lon: 74.0060}
	var sanDiego = geodist.Coord{Lat: 32.7157, Lon: 117.1611}
	miles, km, ok := geodist.VincentyDistance(newYork, sanDiego)
	if !ok {
		fmt.Println("Unable to compute Vincenty Distance.")
		return
	}
	fmt.Printf(" [Vincenty] New York to San Diego: %.3f m, %.3f km\n", miles, km)

	var elPaso = geodist.Coord{Lat: 31.7619, Lon: 106.4850}
	var stLouis = geodist.Coord{Lat: 38.6270, Lon: 90.1994}
	miles, km = geodist.HaversineDistance(elPaso, stLouis)
	fmt.Printf("[Haversine] El Paso to St. Louis:  %.3f m, %.3f km\n", miles, km)
```

## Online Calculators
* **Great Circle**: [NOAA: Latitude/Longitude Distance Calculator](https://www.nhc.noaa.gov/gccalc.shtml)
* **Haversine**: [Moveable Type: Calculate distance, bearing and more between Latitude/Longitude points](https://www.movable-type.co.uk/scripts/latlong.html)
* **Vincenty**: [CQSRG: WGS-84 World Geodetic System Distance Calculator](https://www.cqsrg.org/tools/GCDistance/)

## Acknowledgements
* [Haversine Algorithm](https://gist.github.com/cdipaolo/d3f8db3848278b49db68) in `GoLang`
* [Vincenty Algorithm](https://web.archive.org/web/20181109001358/http://www.5thandpenn.com/GeoMaps/GMapsExamples/distanceComplete2.html) in `JavaScript`


================================================
FILE: example/example.go
================================================
package main

import (
	"fmt"
	"github.com/jftuga/geodist"
)

func main() {
	var newYork = geodist.Coord{Lat: 40.7128, Lon: 74.0060}
	var sanDiego = geodist.Coord{Lat: 32.7157, Lon: 117.1611}
	miles, km, err := geodist.VincentyDistance(newYork, sanDiego)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Printf(" [Vincenty] New York to San Diego: %.3f m, %.3f km\n", miles, km)
	miles, km = geodist.HaversineDistance(newYork, sanDiego)
	fmt.Printf("[Haversine] New York to San Diego: %.3f m, %.3f km\n", miles, km)

	fmt.Println()

	var elPaso = geodist.Coord{Lat: 31.7619, Lon: 106.4850}
	var stLouis = geodist.Coord{Lat: 38.6270, Lon: 90.1994}
	miles, km, err = geodist.VincentyDistance(elPaso, stLouis)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Printf(" [Vincenty] El Paso to St. Louis: %.3f m, %.3f km\n", miles, km)
	miles, km = geodist.HaversineDistance(elPaso, stLouis)
	fmt.Printf("[Haversine] El Paso to St. Louis: %.3f m, %.3f km\n", miles, km)
}


================================================
FILE: go.mod
================================================
module github.com/jftuga/geodist

go 1.17


================================================
FILE: haversine.go
================================================
/*

haversine.go
-John Taylor

Compute the distance between two geographic points when given a pair of latitude-longitude coordinates

Haversine formula:
https://en.wikipedia.org/wiki/Haversine_formula

The code below was adapted from Conner DiPaolo:
https://gist.github.com/cdipaolo/d3f8db3848278b49db68

*/

package geodist

import (
	"math"
)

// adapted from: https://gist.github.com/cdipaolo/d3f8db3848278b49db68
// haversin(θ) function
func hsin(theta float64) float64 {
	return math.Pow(math.Sin(theta/2), 2)
}

// HaversineDistance returns the distance (in miles) between two points of
//	 a given longitude and latitude relatively accurately (using a spherical
//	 approximation of the Earth) through the Haversin Distance Formula for
//	 great arc distance on a sphere with accuracy for small distances
//
// point coordinates are supplied in degrees and converted into rad. in the func
//
// http://en.wikipedia.org/wiki/Haversine_formula
func HaversineDistance(p1, p2 Coord) (float64, float64) {
	// convert to radians
	// must cast radius as float to multiply later
	var la1, lo1, la2, lo2, r float64

	piRad := math.Pi / 180
	la1 = p1.Lat * piRad
	lo1 = p1.Lon * piRad
	la2 = p2.Lat * piRad
	lo2 = p2.Lon * piRad

	r = 6378100 // Earth radius in METERS

	// calculate
	h := hsin(la2-la1) + math.Cos(la1)*math.Cos(la2)*hsin(lo2-lo1)

	meters := 2 * r * math.Asin(math.Sqrt(h))
	kilometers := meters / 1000
	miles := kilometers * 0.621371
	return miles, kilometers
}


================================================
FILE: haversine_test.go
================================================
package geodist

import (
	"testing"
)

func TestHaversineDistance(t *testing.T) {
	// distance NY-SD: 3915340.577 m
	// distance SD-EP: 1011300.217 m
	// distance EP-SL: 1663833.491 m
	// distance SL-NY: 1406519.972 m
	var newYork = Coord{40.7128, 74.0060}
	var sanDiego = Coord{32.7157, 117.1611}
	var elPaso = Coord{31.7619, 106.4850}
	var stLouis = Coord{38.6270, 90.1994}

	var miles, km float64

	miles, km = HaversineDistance(newYork, sanDiego)
	if int(miles) != 2430 || int64(km) != 3911 {
		t.Errorf("Computed values: %v %10f\n", miles, km)
		t.Errorf("Incorrect computation between New York and San Diego: %v %v\n", int(miles), int64(km))
	}

	miles, km = HaversineDistance(sanDiego, elPaso)
	if int(miles) != 627 || int64(km) != 1010 {
		t.Errorf("Computed values: %v %10f\n", miles, km)
		t.Errorf("Incorrect computation between San Diego and El Paso: %v %v\n", int(miles), int64(km))
	}

	miles, km = HaversineDistance(elPaso, stLouis)
	if int(miles) != 1033 || int(km) != 1663 {
		t.Errorf("Computed values: %v %10f\n", miles, km)
		t.Errorf("Incorrect computation between El Paso and St. Louis: %v %v\n", int(miles), int64(km))
	}

	miles, km = HaversineDistance(stLouis, newYork)
	if int(miles) != 872 || int(km) != 1404 {
		t.Errorf("Computed values: %v %10f\n", miles, km)
		t.Errorf("Incorrect computation between St. Louis and New York: %v %v\n", int(miles), int64(km))
	}

	miles, km = HaversineDistance(newYork, newYork)
	if int(miles) != 0 || int(km) != 0 {
		t.Errorf("Computed values: %v %10f\n", miles, km)
		t.Errorf("Incorrect computation between New York and New York: %v %v\n", int(miles), int64(km))
	}
}


================================================
FILE: shared.go
================================================
/*
shared.go
-John Taylor

shared components between the distance algorithms

*/

package geodist

const version string = "1.0.0"

// Coord represents a geographic coordinate
type Coord struct {
	Lat float64
	Lon float64
}


================================================
FILE: vincenty.go
================================================
/*

vincenty.go
-John Taylor

Compute the distance between two geographic points when given a pair of latitude-longitude coordinates

Vincenty formula:
https://en.wikipedia.org/wiki/Vincenty%27s_formulae

The code below was ported from Chris Veness's JavaScript version:
https://web.archive.org/web/20181109001358/http://www.5thandpenn.com/GeoMaps/GMapsExamples/distanceComplete2.html

*/

package geodist

import (
	"errors"
	"math"
)

// these constants are used for vincentyDistance()
// reference: https://en.wikipedia.org/wiki/World_Geodetic_System#1984_version
const a = 6378137
const b = 6356752.3142
const f = 1 / 298.257223563 // WGS-84 ellipsiod

/*
VincentyDistance computes the distances between two georgaphic coordinates

Args:
	p1: the 'starting' point, given in latitude, longitude as a Coord struct

	p2: the 'ending' point

Returns:
	A 3 element tuple: distance between the 2 points given in (1) miles and (2) kilometers
	The 3rd element will return true upon a successful computation or
	false if the algorithm fails to converge. -1, -1, false is returned upon failure
*/
func VincentyDistance(p1, p2 Coord) (float64, float64, error) {
	// convert from degrees to radians
	piRad := math.Pi / 180
	p1.Lat = p1.Lat * piRad
	p1.Lon = p1.Lon * piRad
	p2.Lat = p2.Lat * piRad
	p2.Lon = p2.Lon * piRad

	L := p2.Lon - p1.Lon

	U1 := math.Atan((1 - f) * math.Tan(p1.Lat))
	U2 := math.Atan((1 - f) * math.Tan(p2.Lat))

	sinU1 := math.Sin(U1)
	cosU1 := math.Cos(U1)
	sinU2 := math.Sin(U2)
	cosU2 := math.Cos(U2)

	lambda := L
	lambdaP := 2 * math.Pi
	iterLimit := 20

	var sinLambda, cosLambda, sinSigma float64
	var cosSigma, sigma, sinAlpha, cosSqAlpha, cos2SigmaM, C float64

	for {
		if math.Abs(lambda-lambdaP) > 1e-12 && (iterLimit > 0) {
			iterLimit -= 1
		} else {
			break
		}
		sinLambda = math.Sin(lambda)
		cosLambda = math.Cos(lambda)

		sinSigma = math.Sqrt((cosU2*sinLambda)*(cosU2*sinLambda) + (cosU1*sinU2-sinU1*cosU2*cosLambda)*(cosU1*sinU2-sinU1*cosU2*cosLambda))
		if sinSigma == 0 {
			return 0, 0, nil // co-incident points
		}

		cosSigma = sinU1*sinU2 + cosU1*cosU2*cosLambda
		sigma = math.Atan2(sinSigma, cosSigma)
		sinAlpha = cosU1 * cosU2 * sinLambda / sinSigma
		cosSqAlpha = 1 - sinAlpha*sinAlpha
		cos2SigmaM = cosSigma - 2*sinU1*sinU2/cosSqAlpha
		if math.IsNaN(cos2SigmaM) {
			cos2SigmaM = 0 // equatorial line: cosSqAlpha=0
		}

		C = f / 16 * cosSqAlpha * (4 + f*(4-3*cosSqAlpha))
		lambdaP = lambda
		lambda = L + (1-C)*f*sinAlpha*(sigma+C*sinSigma*(cos2SigmaM+C*cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)))
	}
	if iterLimit == 0 {
		return -1, -1, errors.New("vincenty algorithm failed to converge") // formula failed to converge
	}

	uSq := cosSqAlpha * (a*a - b*b) / (b * b)
	A := 1 + uSq/16384*(4096+uSq*(-768+uSq*(320-175*uSq)))
	B := uSq / 1024 * (256 + uSq*(-128+uSq*(74-47*uSq)))
	deltaSigma := B * sinSigma * (cos2SigmaM + B/4*(cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)-B/6*cos2SigmaM*(-3+4*sinSigma*sinSigma)*(-3+4*cos2SigmaM*cos2SigmaM)))
	meters := b * A * (sigma - deltaSigma)
	kilometers := meters / 1000
	miles := kilometers * 0.621371
	return miles, kilometers, nil
}


================================================
FILE: vincenty_test.go
================================================
package geodist

import (
	"testing"
)

func TestVincentyDistance(t *testing.T) {
	// distance NY-SD: 3915340.577 m
	// distance SD-EP: 1011300.217 m
	// distance EP-SL: 1663833.491 m
	// distance SL-NY: 1406519.972 m
	var newYork = Coord{40.7128, 74.0060}
	var sanDiego = Coord{32.7157, 117.1611}
	var elPaso = Coord{31.7619, 106.4850}
	var stLouis = Coord{38.6270, 90.1994}

	var miles, km float64
	var err error

	miles, km, err = VincentyDistance(newYork, sanDiego)
	if int(miles) != 2432 || int64(km) != 3915 || err != nil {
		t.Errorf("Computed values: %v %10f %v\n", miles, km, err)
		t.Errorf("Incorrect computation between New York and San Diego: %v %v %v\n", int(miles), int64(km), err)
	}

	miles, km, err = VincentyDistance(sanDiego, elPaso)
	if int(miles) != 628 || int64(km) != 1011 || err != nil {
		t.Errorf("Computed values: %v %10f %v\n", miles, km, err)
		t.Errorf("Incorrect computation between San Diego and El Paso: %v %v %v\n", int(miles), int64(km), err)
	}

	miles, km, err = VincentyDistance(elPaso, stLouis)
	if int(miles) != 1033 || int(km) != 1663 || err != nil {
		t.Errorf("Computed values: %v %10f %v\n", miles, km, err)
		t.Errorf("Incorrect computation between El Paso and St. Louis: %v %v %v\n", int(miles), int64(km), err)
	}

	miles, km, err = VincentyDistance(stLouis, newYork)
	if int(miles) != 873 || int(km) != 1406 || err != nil {
		t.Errorf("Computed values: %v %10f %v\n", miles, km, err)
		t.Errorf("Incorrect computation between St. Louis and New York: %v %v %v\n", int(miles), int64(km), err)
	}

	miles, km, err = VincentyDistance(newYork, newYork)
	if int(miles) != 0 || int(km) != 0 || err != nil {
		t.Errorf("Computed values: %v %10f %v\n", miles, km, err)
		t.Errorf("Incorrect computation between New York and New York: %v %v %v\n", int(miles), int64(km), err)
	}
}