gps.go: Fix known S2 mishandling that can lead to an invalid cell

gps.go

@@ -1,54 +1,56 @@
 package exif
 
 import (
-    "fmt"
-    "time"
+	"errors"
+	"fmt"
+	"time"
 
-    "github.com/golang/geo/s1"
-    "github.com/golang/geo/s2"
+	"github.com/golang/geo/s2"
 )
 
+var (
+	ErrGpsCoordinatesNotValid = errors.New("GPS coordinates not valid")
+)
 
 type GpsDegrees struct {
-    Orientation byte
-    Degrees, Minutes, Seconds int
+	Orientation               byte
+	Degrees, Minutes, Seconds int
 }
 
 func (d GpsDegrees) String() string {
-    return fmt.Sprintf("Degrees<O=[%s] D=(%d) M=(%d) S=(%d)>", string([]byte { d.Orientation }), d.Degrees, d.Minutes, d.Seconds)
+	return fmt.Sprintf("Degrees<O=[%s] D=(%d) M=(%d) S=(%d)>", string([]byte{d.Orientation}), d.Degrees, d.Minutes, d.Seconds)
 }
 
 func (d GpsDegrees) Decimal() float64 {
-    decimal := float64(d.Degrees) + float64(d.Minutes) / 60.0 + float64(d.Seconds) / 3600.0
+	decimal := float64(d.Degrees) + float64(d.Minutes)/60.0 + float64(d.Seconds)/3600.0
 
-    if d.Orientation == 'S' || d.Orientation == 'W' {
-        return -decimal
-    } else {
-        return decimal
-    }
+	if d.Orientation == 'S' || d.Orientation == 'W' {
+		return -decimal
+	} else {
+		return decimal
+	}
 }
 
-
 type GpsInfo struct {
-    Latitude, Longitude GpsDegrees
-    Altitude int
-    Timestamp time.Time
+	Latitude, Longitude GpsDegrees
+	Altitude            int
+	Timestamp           time.Time
 }
 
 func (gi *GpsInfo) String() string {
-    return fmt.Sprintf("GpsInfo<LAT=(%.05f) LON=(%.05f) ALT=(%d) TIME=[%s]>", gi.Latitude.Decimal(), gi.Longitude.Decimal(), gi.Altitude, gi.Timestamp)
+	return fmt.Sprintf("GpsInfo<LAT=(%.05f) LON=(%.05f) ALT=(%d) TIME=[%s]>", gi.Latitude.Decimal(), gi.Longitude.Decimal(), gi.Altitude, gi.Timestamp)
 }
 
 func (gi *GpsInfo) S2CellId() s2.CellID {
-    latitude := gi.Latitude.Decimal()
-    longitude := gi.Longitude.Decimal()
+	latitude := gi.Latitude.Decimal()
+	longitude := gi.Longitude.Decimal()
 
-    ll := s2.LatLng{
-        s1.Angle(latitude),
-        s1.Angle(longitude),
-    }
+	ll := s2.LatLngFromDegrees(latitude, longitude)
+	cellId := s2.CellIDFromLatLng(ll)
 
-    ll.Normalized()
+	if cellId.IsValid() == false {
+		panic(ErrGpsCoordinatesNotValid)
+	}
 
-    return s2.CellIDFromLatLng(ll)
+	return cellId
 }