project

README

orb/project

Package orb/project has helper function for projection geometries.

Examples

Project orb.Point to Mercator:

sf := orb.Point{-122.416667, 37.783333}
merc := project.Point(sf, project.WGS84.ToMercator)

fmt.Println(merc)
// Output:
// [-1.3627361035049736e+07 4.548863085837512e+06]

Find centroid of polygon in Mercator projection:

poly := orb.Polygon{
	{
		{-122.4163816, 37.7792782},
		{-122.4162786, 37.7787626},
		{-122.4151027, 37.7789118},
		{-122.4152143, 37.7794274},
		{-122.4163816, 37.7792782},
	},
}

merc := project.Polygon(poly, project.WGS84.ToMercator)
centroid, _ := planar.CentroidArea(merc)

centroid = project.Mercator.ToWGS84(centroid)

fmt.Println(centroid)
// Output:
// [-122.41574403384001 37.77909471899779]

Documentation

Overview

Package project defines projections to and from Mercator and WGS84 along with helpers to apply them to orb geometry types.

Index

• Variables
• func Bound(bound orb.Bound, proj orb.Projection) orb.Bound
• func Collection(c orb.Collection, proj orb.Projection) orb.Collection
• func Geometry(g orb.Geometry, proj orb.Projection) orb.Geometry
• func LineString(ls orb.LineString, proj orb.Projection) orb.LineString
• func MercatorScaleFactor(g orb.Point) float64
• func MultiLineString(mls orb.MultiLineString, proj orb.Projection) orb.MultiLineString
• func MultiPoint(mp orb.MultiPoint, proj orb.Projection) orb.MultiPoint
• func MultiPolygon(mp orb.MultiPolygon, proj orb.Projection) orb.MultiPolygon
• func Point(p orb.Point, proj orb.Projection) orb.Point
• func Polygon(p orb.Polygon, proj orb.Projection) orb.Polygon
• func Ring(r orb.Ring, proj orb.Projection) orb.Ring

Examples

• Point (ToMercator)
• Polygon

Variables

var Mercator = struct {
	ToWGS84 orb.Projection
}{
	ToWGS84: func(p orb.Point) orb.Point {
		return orb.Point{
			180.0 * p[0] / earthRadiusPi,
			180.0 / math.Pi * (2*math.Atan(math.Exp(p[1]/orb.EarthRadius)) - math.Pi/2.0),
		}
	},
}

Mercator performs the Spherical Pseudo-Mercator projection used by most web maps.

var WGS84 = struct {
	// ToMercator projections from WGS to Mercator, used by most web maps
	ToMercator orb.Projection
}{
	ToMercator: func(g orb.Point) orb.Point {
		y := math.Log(math.Tan((90.0+g[1])*math.Pi/360.0)) * orb.EarthRadius
		return orb.Point{
			earthRadiusPi / 180.0 * g[0],
			math.Max(-earthRadiusPi, math.Min(y, earthRadiusPi)),
		}
	},
}

WGS84 is what common uses lon/lat projection.

Functions

func Bound

func Bound(bound orb.Bound, proj orb.Projection) orb.Bound

Bound is a helper to project a rectangle.

func Collection

func Collection(c orb.Collection, proj orb.Projection) orb.Collection

Collection is a helper to project a rectangle.

func Geometry

func Geometry(g orb.Geometry, proj orb.Projection) orb.Geometry

Geometry is a helper to project any geomtry.

func LineString

func LineString(ls orb.LineString, proj orb.Projection) orb.LineString

LineString is a helper to project an entire line string.

func MercatorScaleFactor

func MercatorScaleFactor(g orb.Point) float64

MercatorScaleFactor returns the mercator scaling factor for a given degree latitude.

func MultiLineString

func MultiLineString(mls orb.MultiLineString, proj orb.Projection) orb.MultiLineString

MultiLineString is a helper to project an entire multi linestring.

func MultiPoint

func MultiPoint(mp orb.MultiPoint, proj orb.Projection) orb.MultiPoint

MultiPoint is a helper to project an entire multi point.

func MultiPolygon

func MultiPolygon(mp orb.MultiPolygon, proj orb.Projection) orb.MultiPolygon

MultiPolygon is a helper to project an entire multi polygon.

func Point

func Point(p orb.Point, proj orb.Projection) orb.Point

Point is a helper to project an a point

Example (ToMercator)

package main

import (
	"fmt"

	"github.com/paulmach/orb"
	"github.com/paulmach/orb/project"
)

func main() {
	sf := orb.Point{-122.416667, 37.783333}
	merc := project.Geometry(sf, project.WGS84.ToMercator)

	fmt.Println(merc)
}

Output:

[-1.3627361035049736e+07 4.548863085837512e+06]

func Polygon

func Polygon(p orb.Polygon, proj orb.Projection) orb.Polygon

Polygon is a helper to project an entire polygon.

Example

package main

import (
	"fmt"

	"github.com/paulmach/orb"
	"github.com/paulmach/orb/planar"
	"github.com/paulmach/orb/project"
)

func main() {
	poly := orb.Polygon{
		{
			{-122.4163816, 37.7792782},
			{-122.4162786, 37.7787626},
			{-122.4151027, 37.7789118},
			{-122.4152143, 37.7794274},
			{-122.4163816, 37.7792782},
		},
	}

	merc := project.Polygon(poly, project.WGS84.ToMercator)
	centroid, _ := planar.CentroidArea(merc)

	centroid = project.Mercator.ToWGS84(centroid)
	fmt.Println(centroid)
}

Output:

[-122.41574403384001 37.77909471899779]

func Ring

func Ring(r orb.Ring, proj orb.Projection) orb.Ring

Ring is a helper to project an entire ring.