mirror of https://github.com/tidwall/tile38.git
35 lines
1.3 KiB
Go
35 lines
1.3 KiB
Go
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package geo
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import "math"
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const earthRadius = 6371e3
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func toRadians(deg float64) float64 { return deg * math.Pi / 180 }
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func toDegrees(rad float64) float64 { return rad * 180 / math.Pi }
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// DistanceTo return the distance in meteres between two point.
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func DistanceTo(latA, lonA, latB, lonB float64) (meters float64) {
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φ1 := toRadians(latA)
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λ1 := toRadians(lonA)
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φ2 := toRadians(latB)
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λ2 := toRadians(lonB)
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Δφ := φ2 - φ1
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Δλ := λ2 - λ1
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a := math.Sin(Δφ/2)*math.Sin(Δφ/2) + math.Cos(φ1)*math.Cos(φ2)*math.Sin(Δλ/2)*math.Sin(Δλ/2)
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c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
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return earthRadius * c
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}
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// DestinationPoint return the destination from a point based on a distance and bearing.
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func DestinationPoint(lat, lon, meters, bearingDegrees float64) (destLat, destLon float64) {
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// see http://williams.best.vwh.net/avform.htm#LL
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δ := meters / earthRadius // angular distance in radians
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θ := toRadians(bearingDegrees)
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φ1 := toRadians(lat)
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λ1 := toRadians(lon)
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φ2 := math.Asin(math.Sin(φ1)*math.Cos(δ) + math.Cos(φ1)*math.Sin(δ)*math.Cos(θ))
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λ2 := λ1 + math.Atan2(math.Sin(θ)*math.Sin(δ)*math.Cos(φ1), math.Cos(δ)-math.Sin(φ1)*math.Sin(φ2))
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λ2 = math.Mod(λ2+3*math.Pi, 2*math.Pi) - math.Pi // normalise to -180..+180°
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return toDegrees(φ2), toDegrees(λ2)
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}
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