6257ddba78
The big change is that the GeoJSON package has been completely rewritten to fix a few of geometry calculation bugs, increase performance, and to better follow the GeoJSON spec RFC 7946. GeoJSON updates - A LineString now requires at least two points. - All json members, even foreign, now persist with the object. - The bbox member persists too but is no longer used for geometry calculations. This is change in behavior. Previously Tile38 would treat the bbox as the object's physical rectangle. - Corrections to geometry intersects and within calculations. Faster spatial queries - The performance of Point-in-polygon and object intersect operations are greatly improved for complex polygons and line strings. It went from O(n) to roughly O(log n). - The same for all collection types with many children, including FeatureCollection, GeometryCollection, MultiPoint, MultiLineString, and MultiPolygon. Codebase changes - The pkg directory has been renamed to internal - The GeoJSON internal package has been moved to a seperate repo at https://github.com/tidwall/geojson. It's now vendored. Please look out for higher memory usage for datasets using complex shapes. A complex shape is one that has 64 or more points. For these shapes it's expected that there will be increase of least 54 bytes per point.
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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