mirror of https://github.com/tidwall/tile38.git
96 lines
3.0 KiB
Go
96 lines
3.0 KiB
Go
// Copyright 2018 Joshua J Baker. All rights reserved.
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// Use of this source code is governed by an MIT-style
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// license that can be found in the LICENSE file.
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package geo
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import (
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"math"
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)
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const (
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earthRadius = 6371e3
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radians = math.Pi / 180
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degrees = 180 / math.Pi
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)
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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 := latA * radians
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λ1 := lonA * radians
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φ2 := latB * radians
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λ2 := lonB * radians
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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) +
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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
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// distance and bearing.
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func DestinationPoint(lat, lon, meters, bearingDegrees float64) (
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destLat, destLon float64,
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) {
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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 := bearingDegrees * radians
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φ1 := lat * radians
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λ1 := lon * radians
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φ2 := math.Asin(math.Sin(φ1)*math.Cos(δ) +
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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),
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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 φ2 * degrees, λ2 * degrees
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}
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// BearingTo returns the (initial) bearing from point 'A' to point 'B'.
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func BearingTo(latA, lonA, latB, lonB float64) float64 {
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// tanθ = sinΔλ⋅cosφ2 / cosφ1⋅sinφ2 − sinφ1⋅cosφ2⋅cosΔλ
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// see mathforum.org/library/drmath/view/55417.html for derivation
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φ1 := latA * radians
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φ2 := latB * radians
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Δλ := (lonB - lonA) * radians
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y := math.Sin(Δλ) * math.Cos(φ2)
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x := math.Cos(φ1)*math.Sin(φ2) - math.Sin(φ1)*math.Cos(φ2)*math.Cos(Δλ)
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θ := math.Atan2(y, x)
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return math.Mod(θ*degrees+360, 360)
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}
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// // SegmentIntersectsCircle ...
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// func SegmentIntersectsCircle(
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// startLat, startLon, endLat, endLon, centerLat, centerLon, meters float64,
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// ) bool {
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// // These are faster checks.
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// // If they succeed there's no need do complicate things.
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// if DistanceTo(startLat, startLon, centerLat, centerLon) <= meters {
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// return true
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// }
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// if DistanceTo(endLat, endLon, centerLat, centerLon) <= meters {
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// return true
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// }
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// // Distance between start and end
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// l := DistanceTo(startLat, startLon, endLat, endLon)
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// // Unit direction vector
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// dLat := (endLat - startLat) / l
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// dLon := (endLon - startLon) / l
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// // Point of the line closest to the center
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// t := dLon*(centerLon-startLon) + dLat*(centerLat-startLat)
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// pLat := t*dLat + startLat
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// pLon := t*dLon + startLon
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// if pLon < startLon || pLon > endLon || pLat < startLat || pLat > endLat {
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// // closest point is outside the segment
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// return false
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// }
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// // Distance from the closest point to the center
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// return DistanceTo(centerLat, centerLon, pLat, pLon) <= meters
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// }
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