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core.go
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core.go
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// Package tool copied from https://gist.github.com/antoniomo/3371e44cbe2f0cc75a525aac0d188cfb
package nearest
import (
"errors"
"strconv"
"strings"
"github.com/golang/geo/s1"
"github.com/golang/geo/s2"
log "github.com/sirupsen/logrus"
)
// https://blog.nobugware.com/post/2016/geo_db_s2_geohash_database/
// http://s2geometry.io/devguide/cpp/quickstart
// Tool constants
const (
EarthRadiusKm = 6371.01 // Earth's mean radius, km (according to NASA).
Helsinki = "helsinki"
Oxford = "oxford"
OxfordPubs = "oxford-pubs"
PointDelimiter = "::"
PointsDelimiter = "|"
Tolkien = "tolkien"
)
// Example Points
var (
HelsinkiCenter = "60.1699::24.9384::Helsinki Center"
HelsinkiExamplePoints = "60.2934::25.0378::Vantaa Center|" +
"60.2055::24.6559::Espoo Center|" +
"60.1699::24.9380::Person in Helsinki|" +
// Far points
"50.0::150.0::Seah of Okhotsk|" +
"50.0::-150.0::North Pacific Ocean|" +
"50.0::50.0::Western Kazakhstan|" +
"50.0::-50.0::Labrador Sea"
OxfordExamplePoints = "51.751944::-1.257778::Oxford|" +
"51.7572::-1.2603::The Eagle and Child|" +
"51.507222::-0.1275::London|" +
"51.48::0::Greenwich|" +
"52.205278::0.119167::Cambridge|" +
// Far points
"42.116667::-71.865278::Oxford, Massachusetts|" +
"-43.312778::172.190556::Oxford, New Zealand"
// Pints points
OxfordPubExamplePoints = "51.7572::-1.2603::The Eagle and Child|" +
"51.7550609::-1.2617064::Morse Bar|" +
"51.755::-1.2544::The King's Arms|" +
"51.7546135::-1.2577909::The White Horse|" +
"51.7547::-1.253::The Turf Tavern"
TolkiensHouse = "51.770903::-1.2626219::Tolkien's House"
)
/////////////////////////////////////////////////////////////////////////////
/// Tool Entrypouint /////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////
// RunOptions ...
type RunOptions struct {
CapRadius float64
CenterPoint string
MaxCells int
MaxLevel int
Points string
}
// Run https://godoc.org/github.com/golang/geo/s2#Cap
func Run(opts *RunOptions) {
center := ParsePoint(opts.CenterPoint)
log.Infof("Center cell id: %#v", center)
points := ParsePoints(opts.Points)
points = append(points, center)
s2cap := s2.CapFromCenterAngle(center.CellID.Point(), KmToAngle(opts.CapRadius))
// http://s2geometry.io/resources/s2cell_statistics.html
// Level 12 are about 3 to 6.4km^2 cells
// Level 20 are about 46.41 to 97.3 meter cells
// Since we put a MaxCells of 8, it won't go to the max level if it
// can't approximate the region better anyway.
rc := &s2.RegionCoverer{MaxLevel: opts.MaxLevel, MaxCells: opts.MaxCells}
covering := rc.Covering(s2.Region(s2cap))
for i, cov := range covering {
log.Infof("Covering Cell %d ID: %d Level: %d", i, uint64(cov),
cov.Level())
PointsInCellID(s2cap, cov, center, points)
}
}
/////////////////////////////////////////////////////////////////////////////
/// Point Implementation ////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////
// Point ...
type Point struct {
CellID s2.CellID
LatLon s2.LatLng
Name string
}
// NewPoint ...
func NewPoint(lat, lon float64, name string) Point {
latLon := s2.LatLngFromDegrees(lat, lon)
return Point{
CellID: s2.CellIDFromLatLng(latLon),
LatLon: latLon,
Name: name,
}
}
/////////////////////////////////////////////////////////////////////////////
/// Points Functions ////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////
// PointsInCellID ...
func PointsInCellID(s2cap s2.Cap, cov s2.CellID, center Point, points []Point) {
bmin := uint64(cov.RangeMin())
bmax := uint64(cov.RangeMax())
for _, p := range points {
// This simulates an indexed range query on the DB
if uint64(p.CellID) < bmin || uint64(p.CellID) > bmax {
continue
}
// Only those in range
lat := p.LatLon.Lat.Degrees()
lon := p.LatLon.Lng.Degrees()
log.Infof("Nearby Candidate: %f (lat) %f (lon) %s", lat, lon, p.Name)
log.Infof("Calculated distance to %s: %f (km)", center.Name,
AngleToKm(p.LatLon.Distance(center.LatLon)))
log.Info("False positive? ", !s2cap.ContainsPoint(p.CellID.Point()))
}
}
/////////////////////////////////////////////////////////////////////////////
/// CLI Helper Functions ////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////
// ParsePoint ...
func ParsePoint(delimited string) Point {
log.Debugf("Pasring point '%s' ...", delimited)
var latArg, lonArg, name string
err := Splitter(delimited, PointSplitterOpts, &latArg, &lonArg, &name)
if err != nil {
log.Fatal(err)
}
switch {
case latArg == Helsinki:
return ParsePoint(HelsinkiCenter)
case latArg == Tolkien:
return ParsePoint(TolkiensHouse)
}
lat, lon := ConvertLatLon(latArg, lonArg)
return NewPoint(lat, lon, name)
}
// ParsePoints ...
func ParsePoints(delimited string) []Point {
log.Debugf("Pasring points '%s' ...", delimited)
args := strings.Split(delimited, PointsDelimiter)
alias := args[0]
switch {
case alias == Helsinki:
return ParsePoints(HelsinkiExamplePoints)
case alias == Oxford:
return ParsePoints(OxfordExamplePoints)
case alias == OxfordPubs:
return ParsePoints(OxfordPubExamplePoints)
default:
points := make([]Point, len(args))
for i, p := range args {
points[i] = ParsePoint(p)
}
return points
}
}
/////////////////////////////////////////////////////////////////////////////
/// Utility Functions ///////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////
// KmToAngle converts a distance on the Earth's surface to an angle.
// https://github.com/golang/geo/blob/23949e136d58aeb8aa39844a312b68d90c4eb8aa/s2/s2_test.go#L38-L43
func KmToAngle(km float64) s1.Angle {
return s1.Angle(km / EarthRadiusKm)
}
// AngleToKm ...
func AngleToKm(angle s1.Angle) float64 {
return EarthRadiusKm * float64(angle)
}
// SplitterOpts ...
type SplitterOpts struct {
Delimiter string
MinVars int
MaxVars int
}
// PointSplitterOpts ...
var PointSplitterOpts = &SplitterOpts{
MinVars: 2,
MaxVars: 3,
Delimiter: PointDelimiter,
}
// Splitter ...
func Splitter(s string, opts *SplitterOpts, vars ...*string) error {
parts := strings.Split(s, opts.Delimiter)
switch {
case len(vars) < opts.MinVars:
return errors.New("Too few variable pointers were passed")
case len(vars) > opts.MaxVars:
return errors.New("Too many variable pointers were passed")
case len(parts) > opts.MaxVars:
return errors.New("Too many delimited items")
default:
for i, str := range parts {
*vars[i] = str
}
}
return nil
}
// ConvertLatLon ...
func ConvertLatLon(lat, lon string) (float64, float64) {
lat64, err := strconv.ParseFloat(lat, 64)
if err != nil {
log.Fatal(err)
}
lon64, err := strconv.ParseFloat(lon, 64)
if err != nil {
log.Fatal(err)
}
return lat64, lon64
}