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

gps.go

@@ -1,13 +1,16 @@
 package exif
 
 import (
+	"errors"
 	"fmt"
 	"time"
 
-    "github.com/golang/geo/s1"
 	"github.com/golang/geo/s2"
 )
 
+var (
+	ErrGpsCoordinatesNotValid = errors.New("GPS coordinates not valid")
+)
 
 type GpsDegrees struct {
 	Orientation               byte
@@ -28,7 +31,6 @@ func (d GpsDegrees) Decimal() float64 {
 	}
 }
 
-
 type GpsInfo struct {
 	Latitude, Longitude GpsDegrees
 	Altitude            int
@@ -43,12 +45,12 @@ func (gi *GpsInfo) S2CellId() s2.CellID {
 	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)
+
+	if cellId.IsValid() == false {
+		panic(ErrGpsCoordinatesNotValid)
 	}
 
-    ll.Normalized()
-
-    return s2.CellIDFromLatLng(ll)
+	return cellId
 }