gtsocial-umbx

latlng.go (3456B)

---

 // Copyright 2014 Google Inc. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 package s2
 
 import (
 	"fmt"
 	"math"
 
 	"github.com/golang/geo/r3"
 	"github.com/golang/geo/s1"
 )
 
 const (
 	northPoleLat = s1.Angle(math.Pi/2) * s1.Radian
 	southPoleLat = -northPoleLat
 )
 
 // LatLng represents a point on the unit sphere as a pair of angles.
 type LatLng struct {
 	Lat, Lng s1.Angle
 }
 
 // LatLngFromDegrees returns a LatLng for the coordinates given in degrees.
 func LatLngFromDegrees(lat, lng float64) LatLng {
 	return LatLng{s1.Angle(lat) * s1.Degree, s1.Angle(lng) * s1.Degree}
 }
 
 // IsValid returns true iff the LatLng is normalized, with Lat ∈ [-π/2,π/2] and Lng ∈ [-π,π].
 func (ll LatLng) IsValid() bool {
 	return math.Abs(ll.Lat.Radians()) <= math.Pi/2 && math.Abs(ll.Lng.Radians()) <= math.Pi
 }
 
 // Normalized returns the normalized version of the LatLng,
 // with Lat clamped to [-π/2,π/2] and Lng wrapped in [-π,π].
 func (ll LatLng) Normalized() LatLng {
 	lat := ll.Lat
 	if lat > northPoleLat {
 		lat = northPoleLat
 	} else if lat < southPoleLat {
 		lat = southPoleLat
 	}
 	lng := s1.Angle(math.Remainder(ll.Lng.Radians(), 2*math.Pi)) * s1.Radian
 	return LatLng{lat, lng}
 }
 
 func (ll LatLng) String() string { return fmt.Sprintf("[%v, %v]", ll.Lat, ll.Lng) }
 
 // Distance returns the angle between two LatLngs.
 func (ll LatLng) Distance(ll2 LatLng) s1.Angle {
 	// Haversine formula, as used in C++ S2LatLng::GetDistance.
 	lat1, lat2 := ll.Lat.Radians(), ll2.Lat.Radians()
 	lng1, lng2 := ll.Lng.Radians(), ll2.Lng.Radians()
 	dlat := math.Sin(0.5 * (lat2 - lat1))
 	dlng := math.Sin(0.5 * (lng2 - lng1))
 	x := dlat*dlat + dlng*dlng*math.Cos(lat1)*math.Cos(lat2)
 	return s1.Angle(2*math.Atan2(math.Sqrt(x), math.Sqrt(math.Max(0, 1-x)))) * s1.Radian
 }
 
 // NOTE(mikeperrow): The C++ implementation publicly exposes latitude/longitude
 // functions. Let's see if that's really necessary before exposing the same functionality.
 
 func latitude(p Point) s1.Angle {
 	return s1.Angle(math.Atan2(p.Z, math.Sqrt(p.X*p.X+p.Y*p.Y))) * s1.Radian
 }
 
 func longitude(p Point) s1.Angle {
 	return s1.Angle(math.Atan2(p.Y, p.X)) * s1.Radian
 }
 
 // PointFromLatLng returns an Point for the given LatLng.
 // The maximum error in the result is 1.5 * dblEpsilon. (This does not
 // include the error of converting degrees, E5, E6, or E7 into radians.)
 func PointFromLatLng(ll LatLng) Point {
 	phi := ll.Lat.Radians()
 	theta := ll.Lng.Radians()
 	cosphi := math.Cos(phi)
 	return Point{r3.Vector{math.Cos(theta) * cosphi, math.Sin(theta) * cosphi, math.Sin(phi)}}
 }
 
 // LatLngFromPoint returns an LatLng for a given Point.
 func LatLngFromPoint(p Point) LatLng {
 	return LatLng{latitude(p), longitude(p)}
 }
 
 // ApproxEqual reports whether the latitude and longitude of the two LatLngs
 // are the same up to a small tolerance.
 func (ll LatLng) ApproxEqual(other LatLng) bool {
 	return ll.Lat.ApproxEqual(other.Lat) && ll.Lng.ApproxEqual(other.Lng)
 }