Go implementation of the geodesic routines from GeographicLib

Josh Baker

Last update: Dec 23, 2022

Comments: 2

geodesic

This package is a Go implementation of the geodesic routines from GeographicLib.

Features

Pure Go implementation
Distance calculations with nanometer precision
Calculate the area and perimeter of a polygon
Get the length of a polyline
Direct and inverse solutions

Installing

To start using geodesic, install Go and run go get:

$ go get -u github.com/tidwall/geodesic

This will retrieve the library.

Using

All operations are performed on an Ellipsoid object.

To create a custom ellipsoid by calling geodesic.NewEllipsoid

// The first argument is the radius and the second is the flattening.
myEllipsoid := geodesic.NewEllipsoid(6378137.0, 1.0/298.257223563)

Or, you can simply use the built-in geodesic.WGS84 ellipsoid, which conforms to the WGS84 standard.

Examples

Calculate distance between two points.

var dist float64
geodesic.WGS84.Inverse(33.4911, -112.4223, 32.1189, -113.1123, &dist, nil, nil)
fmt.Printf("%f meters\n", dist)
// output: 
// 165330.214571 meters

Calculate initial azimuth from point A to point B.

var azi float64
geodesic.WGS84.Inverse(33.4911, -112.4223, 32.1189, -113.1123, nil, &azi, nil)
fmt.Printf("%f degrees\n", azi)
// output:
// -156.803310 degrees

Calculate final azimuth from point A to point B.

var azi float64
geodesic.WGS84.Inverse(33.4911, -112.4223, 32.1189, -113.1123, nil, nil, &azi)
fmt.Printf("%f degrees\n", azi)
// output:
// -157.177169 degrees

Calculate distance and azimuths at the same time.

var dist, azi1, azi2 float64
geodesic.WGS84.Inverse(33.4911, -112.4223, 32.1189, -113.1123, &dist, &azi1, &azi2)
fmt.Printf("%f meters, %f degrees, %f degrees\n", dist,azi1,azi2)
// output:
// 165330.214571 meters, -156.803310 degrees, -157.177169 degrees

Calculate destination using an initial point, azimuth, and distance.

var lat, lon float64
geodesic.WGS84.Direct(33.4911, -112.4223, -156.803310, 165330.214571, &lat, &lon, nil)
fmt.Printf("%f, %f\n", lat, lon)
// output: 
// 32.118900, -113.112300

Calculate the area and perimeter of a polygon.

// Arizona
poly := WGS84.PolygonInit(false)
poly.AddPoint(36.99377, -109.050292)
poly.AddPoint(36.96744, -114.049072)
poly.AddPoint(36.26199, -114.016113)
poly.AddPoint(36.08462, -114.279785)
poly.AddPoint(36.11125, -114.730224)
poly.AddPoint(34.86790, -114.631347)
poly.AddPoint(34.47939, -114.367675)
poly.AddPoint(34.29806, -114.104003)
poly.AddPoint(33.89777, -114.532470)
poly.AddPoint(33.58716, -114.543457)
poly.AddPoint(33.35806, -114.708251)
poly.AddPoint(33.09154, -114.708251)
poly.AddPoint(32.87036, -114.444580)
poly.AddPoint(32.74108, -114.719238)
poly.AddPoint(32.50049, -114.818115)
poly.AddPoint(31.33487, -111.093749)
poly.AddPoint(31.35363, -109.050292)
poly.AddPoint(36.99377, -109.050292)
var area, perimeter float64
poly.Compute(false, false, &area, &perimeter)
fmt.Printf("%f area (km²), %f perimeter (meters)\n", area/1000000, perimeter)
// output:
// 294838.722804 area (km²), 2254910.021767 perimeter (meters)

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Comments

Different order of adding points leads to wrong area calculation

In the sample code below, the area calculated for the second case seems to be wrong.

func TestArea2(t *testing.T) {
	var area, perimeter float64

	poly := geodesic.WGS84.PolygonInit(false)
	poly.AddPoint(10, 10)
	poly.AddPoint(10, 20)
	poly.AddPoint(20, 20)
	poly.AddPoint(20, 10)

	poly.Compute(false, false, &area, &perimeter)

	fmt.Printf("%f, %f\n", area, perimeter)

	poly = geodesic.WGS84.PolygonInit(false)
	poly.AddPoint(10, 10)
	poly.AddPoint(20, 10)
	poly.AddPoint(20, 20)
	poly.AddPoint(10, 20)

	poly.Compute(false, false, &area, &perimeter)

	fmt.Printf("%f, %f\n", area, perimeter)
}

Outputs:

1190968350339.391846,   4355689.472548
508874653373749.062500, 4355689.472548

[feature] geodesic buffer

Thank you for providing this valuable package in Go. For geodesic calculation, one important feature is the geodesic buffer (on sphere). Currently, there is no Go library that works for this feature. ArcGIS does provide some APIs, but they are not flexible enough. I was wondering if you have any plans to add relevant functions in this package?

Go implementation of the geodesic routines from GeographicLib

geodesic

Features

Installing

Using

Examples

Owner

Josh Baker

Similar Resources

Comments

Different order of adding points leads to wrong area calculation

[feature] geodesic buffer

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