Documentation
¶
Overview ¶
Package earth implements functions for working with the planet Earth modeled as a sphere.
Index ¶
- Constants
- func AngleFromLength(d unit.Length) s1.Angle
- func AreaFromSteradians(s float64) unit.Area
- func InitialBearingFromLatLngs(a, b s2.LatLng) s1.Angle
- func LengthFromAngle(a s1.Angle) unit.Length
- func LengthFromLatLngs(a, b s2.LatLng) unit.Length
- func LengthFromPoints(a, b s2.Point) unit.Length
- func SteradiansFromArea(a unit.Area) float64
Examples ¶
Constants ¶
const ( // Radius is the Earth's mean radius, which is the radius of the // equivalent sphere with the same surface area. According to NASA, // this value is 6371.01 +/- 0.02 km. The equatorial radius is 6378.136 // km, and the polar radius is 6356.752 km. They differ by one part in // 298.257. // // Reference: http://ssd.jpl.nasa.gov/phys_props_earth.html, which // quotes Yoder, C.F. 1995. "Astrometric and Geodetic Properties of // Earth and the Solar System" in Global Earth Physics, A Handbook of // Physical Constants, AGU Reference Shelf 1, American Geophysical // Union, Table 2. // // This value is the same as in s2earth.h and S2Earth.java in order to be // able to make consistent conversions across programming languages. Radius = 6371.01 * unit.Kilometer LowestAltitude = -10898 * unit.Meter HighestAltitude = 8848 * unit.Meter )
Variables ¶
This section is empty.
Functions ¶
func AngleFromLength ¶
AngleFromLength returns the angle from a given distance on the spherical earth's surface.
Example ¶
package main
import (
"fmt"
"github.com/golang/geo/earth"
"github.com/google/go-units/unit"
)
func main() {
length := 500 * unit.Mile
angle := earth.AngleFromLength(length)
fmt.Printf("I would walk 500 miles (%.4f rad)", angle.Radians())
}
Output: I would walk 500 miles (0.1263 rad)
func AreaFromSteradians ¶
AreaFromSteradians returns the area on the spherical Earth's surface covered by s steradians, as returned by Area() methods on s2 geometry types.
Example ¶
package main
import (
"fmt"
"github.com/golang/geo/earth"
"github.com/golang/geo/s2"
)
func main() {
bermuda := s2.PointFromLatLng(s2.LatLngFromDegrees(32.361457, -64.663495))
culebra := s2.PointFromLatLng(s2.LatLngFromDegrees(18.311199, -65.300765))
miami := s2.PointFromLatLng(s2.LatLngFromDegrees(25.802018, -80.269892))
triangle := s2.PolygonFromLoops(
[]*s2.Loop{s2.LoopFromPoints([]s2.Point{bermuda, miami, culebra})})
area := earth.AreaFromSteradians(triangle.Area())
fmt.Printf("Bermuda Triangle is %.2f square miles", area.SquareMiles())
}
Output: Bermuda Triangle is 464541.15 square miles
func InitialBearingFromLatLngs ¶
InitialBearingFromLatLngs computes the initial bearing from a to b.
This is the bearing an observer at point a has when facing point b. A bearing of 0 degrees is north, and it increases clockwise (90 degrees is east, etc).
If a == b, a == -b, or a is one of the Earth's poles, the return value is undefined.
Example ¶
package main
import (
"fmt"
"github.com/golang/geo/earth"
"github.com/golang/geo/s2"
)
func main() {
christchurch := s2.LatLngFromDegrees(-43.491402, 172.522275)
riogrande := s2.LatLngFromDegrees(-53.777156, -67.734719)
bearing := earth.InitialBearingFromLatLngs(christchurch, riogrande)
fmt.Printf("Head southeast (%.2f°)", bearing.Degrees())
}
Output: Head southeast (146.90°)
func LengthFromAngle ¶
LengthFromAngle returns the distance on the spherical earth's surface from a given angle.
Example ¶
package main
import (
"fmt"
"github.com/golang/geo/earth"
"github.com/golang/geo/s1"
)
func main() {
angle := 2 * s1.Degree
length := earth.LengthFromAngle(angle)
fmt.Printf("2° is %.0f miles", length.Miles())
}
Output: 2° is 138 miles
func LengthFromLatLngs ¶
LengthFromLatLngs returns the distance on the spherical earth's surface between two LatLngs.
Example ¶
package main
import (
"fmt"
"github.com/golang/geo/earth"
"github.com/golang/geo/s2"
)
func main() {
chukchi := s2.LatLngFromDegrees(66.025893, -169.699684)
seward := s2.LatLngFromDegrees(65.609727, -168.093694)
length := earth.LengthFromLatLngs(chukchi, seward)
fmt.Printf("Bering Strait is %.0f feet", length.Feet())
}
Output: Bering Strait is 283979 feet
func LengthFromPoints ¶
LengthFromPoints returns the distance between two points on the spherical earth's surface.
Example ¶
package main
import (
"fmt"
"math"
"github.com/golang/geo/earth"
"github.com/golang/geo/s2"
)
func main() {
equator := s2.PointFromCoords(1, 0, 0)
pole := s2.PointFromCoords(0, 1, 0)
length := earth.LengthFromPoints(equator, pole)
fmt.Printf("Equator to pole is %.2f km, π/2*Earth radius is %.2f km",
length.Kilometers(), math.Pi/2*earth.Radius.Kilometers())
}
Output: Equator to pole is 10007.56 km, π/2*Earth radius is 10007.56 km
func SteradiansFromArea ¶
SteradiansFromArea returns the number of steradians covered by an area on the spherical Earth's surface. The value will be between 0 and 4 * math.Pi if a does not exceed the area of the Earth.
Example ¶
package main
import (
"fmt"
"github.com/golang/geo/earth"
"github.com/golang/geo/s2"
"github.com/google/go-units/unit"
)
func main() {
steradians := earth.SteradiansFromArea(unit.SquareCentimeter)
fmt.Printf("1 square centimeter is %g steradians, close to a level %d cell",
steradians, s2.AvgAreaMetric.ClosestLevel(steradians))
}
Output: 1 square centimeter is 2.4636750563592804e-18 steradians, close to a level 30 cell
Types ¶
This section is empty.
Source Files