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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
package geo
import (
"math"
"strconv"
"strings"
"unicode"
)
const (
Degree Degrees = 1
Radian Radians = 1
Turn Turns = 1
Meter Distance = 1
)
// Degrees represents a latitude or longitude, in decimal degrees.
type Degrees float64
// ParseDegrees parses s as decimal degrees.
func ParseDegrees(s string) (Degrees, error) {
s = strings.TrimSuffix(s, "°")
f, err := strconv.ParseFloat(s, 64)
return Degrees(f), err
}
// MustParseDegrees parses s as decimal degrees, but panics on error.
func MustParseDegrees(s string) Degrees {
d, err := ParseDegrees(s)
if err != nil {
panic(err)
}
return d
}
// String implements the [Stringer] interface. The output is formatted in
// decimal degrees, prefixed by either the appropriate + or - sign, and suffixed
// by a ° degree symbol.
func (d Degrees) String() string {
b, _ := d.AppendText(nil)
b = append(b, []byte("°")...)
return string(b)
}
// AppendText implements [encoding.TextAppender]. The output is formatted in
// decimal degrees, prefixed by either the appropriate + or - sign.
func (d Degrees) AppendText(b []byte) ([]byte, error) {
b = d.AppendZeroPaddedText(b, 0)
return b, nil
}
// AppendZeroPaddedText appends d formatted as decimal degrees to b. The number of
// integer digits will be zero-padded to nint.
func (d Degrees) AppendZeroPaddedText(b []byte, nint int) []byte {
n := float64(d)
if math.IsInf(n, 0) || math.IsNaN(n) {
return strconv.AppendFloat(b, n, 'f', -1, 64)
}
sign := byte('+')
if math.Signbit(n) {
sign = '-'
n = -n
}
b = append(b, sign)
pad := nint - 1
for nn := n / 10; nn >= 1 && pad > 0; nn /= 10 {
pad--
}
for range pad {
b = append(b, '0')
}
return strconv.AppendFloat(b, n, 'f', -1, 64)
}
// Radians converts d into radians.
func (d Degrees) Radians() Radians {
return Radians(d * math.Pi / 180.0)
}
// Turns converts d into a number of turns.
func (d Degrees) Turns() Turns {
return Turns(d / 360.0)
}
// Radians represents a latitude or longitude, in radians.
type Radians float64
// ParseRadians parses s as radians.
func ParseRadians(s string) (Radians, error) {
s = strings.TrimSuffix(s, "rad")
s = strings.TrimRightFunc(s, unicode.IsSpace)
f, err := strconv.ParseFloat(s, 64)
return Radians(f), err
}
// MustParseRadians parses s as radians, but panics on error.
func MustParseRadians(s string) Radians {
r, err := ParseRadians(s)
if err != nil {
panic(err)
}
return r
}
// String implements the [Stringer] interface.
func (r Radians) String() string {
return strconv.FormatFloat(float64(r), 'f', -1, 64) + " rad"
}
// Degrees converts r into decimal degrees.
func (r Radians) Degrees() Degrees {
return Degrees(r * 180.0 / math.Pi)
}
// Turns converts r into a number of turns.
func (r Radians) Turns() Turns {
return Turns(r / 2 / math.Pi)
}
// Turns represents a number of complete revolutions around a sphere.
type Turns float64
// String implements the [Stringer] interface.
func (o Turns) String() string {
return strconv.FormatFloat(float64(o), 'f', -1, 64)
}
// Degrees converts t into decimal degrees.
func (o Turns) Degrees() Degrees {
return Degrees(o * 360.0)
}
// Radians converts t into radians.
func (o Turns) Radians() Radians {
return Radians(o * 2 * math.Pi)
}
// Distance represents a great-circle distance in meters.
type Distance float64
// ParseDistance parses s as distance in meters.
func ParseDistance(s string) (Distance, error) {
s = strings.TrimSuffix(s, "m")
s = strings.TrimRightFunc(s, unicode.IsSpace)
f, err := strconv.ParseFloat(s, 64)
return Distance(f), err
}
// MustParseDistance parses s as distance in meters, but panics on error.
func MustParseDistance(s string) Distance {
d, err := ParseDistance(s)
if err != nil {
panic(err)
}
return d
}
// String implements the [Stringer] interface.
func (d Distance) String() string {
return strconv.FormatFloat(float64(d), 'f', -1, 64) + "m"
}
// DistanceOnEarth converts t turns into the great-circle distance, in meters.
func DistanceOnEarth(t Turns) Distance {
return Distance(t) * EarthMeanCircumference
}
// Earth Fact Sheet
// https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
const (
// EarthMeanRadius is the volumetric mean radius of the Earth.
EarthMeanRadius = 6_371_000 * Meter
// EarthMeanCircumference is the volumetric mean circumference of the Earth.
EarthMeanCircumference = 2 * math.Pi * EarthMeanRadius
// earthEquatorialRadius is the equatorial radius of the Earth.
earthEquatorialRadius = 6_378_137 * Meter
// earthEquatorialCircumference is the equatorial circumference of the Earth.
earthEquatorialCircumference = 2 * math.Pi * earthEquatorialRadius
// earthPolarRadius is the polar radius of the Earth.
earthPolarRadius = 6_356_752 * Meter
// earthPolarCircumference is the polar circumference of the Earth.
earthPolarCircumference = 2 * math.Pi * earthPolarRadius
)
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