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package maidenhead
import (
"fmt"
"math"
)
const (
// Earth radius
r = 6371
)
var compassBearing = []struct {
label string
start, ended float64
}{
{"N", 000.00, 011.25}, {"NNE", 011.25, 033.75}, {"NE", 033.75, 056.25}, {"ENE", 056.25, 078.75},
{"E", 078.75, 101.25}, {"ESE", 101.25, 123.75}, {"SE", 123.75, 146.25}, {"SSE", 146.25, 168.75},
{"S", 168.75, 191.25}, {"SSW", 191.25, 213.75}, {"SW", 213.75, 236.25}, {"WSW", 236.25, 258.75},
{"W", 258.75, 281.25}, {"WNW", 281.25, 303.75}, {"NW", 303.75, 326.25}, {"NNW", 326.25, 348.75},
{"N", 348.75, 360.00},
}
// Point is a geographical point on the map.
type Point struct {
Latitude float64
Longitude float64
}
// NewPoint returns a new Point structure with given latitude and longitude.
func NewPoint(latitude, longitude float64) Point {
return Point{latitude, longitude}
}
// ParseLocator parses a Maidenhead Locator with permissive rule matching.
func ParseLocator(locator string) (Point, error) {
return parseLocator(locator, false)
}
// ParseLocatorStrict parses a Maidenhead Locator with strict rule matching.
func ParseLocatorStrict(locator string) (Point, error) {
return parseLocator(locator, true)
}
// EqualTo returns true if the coordinates point to the same geographical location.
func (p Point) EqualTo(other Point) bool {
var (
dlat = p.Latitude - other.Latitude
dlng = p.Longitude - other.Longitude
)
for dlat < -180.0 {
dlat += 360.0
}
for dlat > 180.0 {
dlat -= 360.0
}
for dlng < -90.0 {
dlng += 90.0
}
for dlng > 90.0 {
dlng -= 90.0
}
return dlat == 0.0 && dlng == 0.0
}
// Bearing calculates the (approximate) bearing to another heading.
func (p Point) Bearing(heading Point) float64 {
var (
hn = p.Latitude / 180 * math.Pi
he = p.Longitude / 180 * math.Pi
n = heading.Latitude / 180 * math.Pi
e = heading.Longitude / 180 * math.Pi
co = math.Cos(he-e)*math.Cos(hn)*math.Cos(n) + math.Sin(hn)*math.Sin(n)
ca = math.Atan(math.Abs(math.Sqrt(1-co*co) / co))
)
if co < 0.0 {
ca = math.Pi - ca
}
var si = math.Sin(e-he) * math.Cos(n) * math.Cos(hn)
co = math.Sin(n) - math.Sin(hn)*math.Cos(ca)
var az = math.Atan(math.Abs(si / co))
if co < 0.0 {
az = math.Pi - az
}
if si < 0.0 {
az = -az
}
if az < 0.0 {
az = az + 2.0 + math.Pi
}
return az * 180 / math.Pi
}
// CompassBearing returns the compass bearing to a heading.
func (p Point) CompassBearing(heading Point) string {
bearing := p.Bearing(heading)
for bearing < 0.0 {
bearing += 360.0
}
for bearing > 360.0 {
bearing -= 360.0
}
for _, compass := range compassBearing {
if bearing >= compass.start && bearing <= compass.ended {
return compass.label
}
}
// Should never reach
return ""
}
// Distance calculates the (approximate) distance to another point in km.
func (p Point) Distance(other Point) float64 {
var (
hn = p.Latitude / 180 * math.Pi
he = p.Longitude / 180 * math.Pi
n = other.Latitude / 180 * math.Pi
e = other.Longitude / 180 * math.Pi
co = math.Cos(he-e)*math.Cos(hn)*math.Cos(n) + math.Sin(hn)*math.Sin(n)
ca = math.Atan(math.Abs(math.Sqrt(1-co*co) / co))
)
if co < 0.0 {
ca = math.Pi - ca
}
return r * ca
}
// GridSquare returns a Maidenhead Locator for the point coordinates.
func (p Point) GridSquare() (string, error) {
return locator(p, SubSquarePrecision)
}
// Locator returns a Maidenhead Locator for the point coordinates with
// specified precision
func (p Point) Locator(precision int) (string, error) {
return locator(p, precision)
}
// String returns a stringified Point structure.
func (p Point) String() string {
return fmt.Sprintf("Point(%f, %f)", p.Latitude, p.Longitude)
}
|
