add support for customizing unit used in distance sorting

geo/geo_dist.go

@@ -15,6 +15,7 @@
 package geo
 
 import (
+	"fmt"
 	"math"
 	"strconv"
 	"strings"
@@ -67,9 +68,23 @@ func ParseDistance(d string) (float64, error) {
 	return parsedNum, nil
 }
 
+// ParseDistanceUnit attempts to parse a distance unit and return the
+// multiplier for converting this to meters.  If the unit cannot be parsed
+// then 0 and the error message is returned.
+func ParseDistanceUnit(u string) (float64, error) {
+	for _, unit := range distanceUnits {
+		for _, unitSuffix := range unit.suffixes {
+			if u == unitSuffix {
+				return unit.conv, nil
+			}
+		}
+	}
+	return 0, fmt.Errorf("unknown distance unit: %s", u)
+}
+
 // Haversin computes the distance between two points.
 // This implemenation uses the sloppy math implemenations which trade off
-// accuracy for performance.
+// accuracy for performance.  The distance returned is in kilometers.
 func Haversin(lon1, lat1, lon2, lat2 float64) float64 {
 	x1 := lat1 * degreesToRadian
 	x2 := lat2 * degreesToRadian

geo/geo_dist_test.go

@@ -15,6 +15,7 @@
 package geo
 
 import (
+	"fmt"
 	"math"
 	"reflect"
 	"strconv"
@@ -46,6 +47,30 @@ func TestParseDistance(t *testing.T) {
 	}
 }
 
+func TestParseDistanceUnit(t *testing.T) {
+	tests := []struct {
+		dist    string
+		want    float64
+		wantErr error
+	}{
+		{"mi", 1609.344, nil},
+		{"m", 1, nil},
+		{"km", 1000, nil},
+		{"", 0, fmt.Errorf("unknown distance unit: ")},
+		{"kam", 0, fmt.Errorf("unknown distance unit: kam")},
+	}
+
+	for _, test := range tests {
+		got, err := ParseDistanceUnit(test.dist)
+		if !reflect.DeepEqual(err, test.wantErr) {
+			t.Errorf("expected err: %v, got %v for %s", test.wantErr, err, test.dist)
+		}
+		if got != test.want {
+			t.Errorf("expected distance %f got %f for %s", test.want, got, test.dist)
+		}
+	}
+}
+
 func TestHaversinDistance(t *testing.T) {
 	earthRadiusKMs := 6378.137
 	halfCircle := earthRadiusKMs * math.Pi

geo/sloppy.go

@@ -137,7 +137,7 @@ func init() {
 }
 
 // earthDiameter returns an estimation of the earth's diameter at the specified
-// latitude
+// latitude in kilometers
 func earthDiameter(lat float64) float64 {
 	index := math.Mod(math.Abs(lat)*radiusIndexer+0.5, float64(len(earthDiameterPerLatitude)))
 	if math.IsNaN(index) {

search/sort.go

@@ -62,12 +62,22 @@ func ParseSearchSortObj(input map[string]interface{}) (SearchSort, error) {
 		if !foundLocation {
 			return nil, fmt.Errorf("unable to parse geo_distance location")
 		}
-		return &SortGeoDistance{
-			Field: field,
-			Desc:  descending,
-			lon:   lon,
-			lat:   lat,
-		}, nil
+		rvd := &SortGeoDistance{
+			Field:    field,
+			Desc:     descending,
+			lon:      lon,
+			lat:      lat,
+			unitMult: 1.0,
+		}
+		if distUnit, ok := input["unit"].(string); ok {
+			var err error
+			rvd.unitMult, err = geo.ParseDistanceUnit(distUnit)
+			if err != nil {
+				return nil, err
+			}
+			rvd.Unit = distUnit
+		}
+		return rvd, nil
 	case "field":
 		field, ok := input["field"].(string)
 		if !ok {
@@ -546,11 +556,13 @@ var maxDistance = string(numeric.MustNewPrefixCodedInt64(math.MaxInt64, 0))
 //   Field is the name of the field
 //   Descending reverse the sort order (default false)
 type SortGeoDistance struct {
-	Field  string
-	Desc   bool
-	values []string
-	lon    float64
-	lat    float64
+	Field    string
+	Desc     bool
+	Unit     string
+	values   []string
+	lon      float64
+	lat      float64
+	unitMult float64
 }
 
 // UpdateVisitor notifies this sort field that in this document
@@ -581,7 +593,13 @@ func (s *SortGeoDistance) Value(i *DocumentMatch) string {
 	docLat := geo.MortonUnhashLat(uint64(i64))
 
 	dist := geo.Haversin(s.lon, s.lat, docLon, docLat)
-	return string(numeric.MustNewPrefixCodedInt64(int64(dist), 0))
+	// dist is returned in km, so convert to m
+	dist *= 1000
+	if s.unitMult != 0 {
+		dist /= s.unitMult
+	}
+	distInt64 := numeric.Float64ToInt64(dist)
+	return string(numeric.MustNewPrefixCodedInt64(distInt64, 0))
 }
 
 // Descending determines the order of the sort
@@ -628,6 +646,9 @@ func (s *SortGeoDistance) MarshalJSON() ([]byte, error) {
 			"lat": s.lat,
 		},
 	}
+	if s.Unit != "" {
+		sfm["unit"] = s.Unit
+	}
 	if s.Desc {
 		sfm["desc"] = true
 	}