Search: improve radius approximation for "lat" and "lng" filters #3558

Signed-off-by: Michael Mayer <michael@photoprism.app>

internal/search/photos_test.go

@@ -639,7 +639,7 @@ func TestPhotos(t *testing.T) {
 	})
 	t.Run("form.Lat and form.Lng", func(t *testing.T) {
 		var f form.SearchPhotos
-		f.Query = "Lat:33.45343166666667 Lng:25.764711666666667 Dist:2000"
+		f.Query = "Lat:33.45343166666667 Lng:25.764711666666667 Dist:4000"
 		f.Count = 10
 		f.Offset = 0
 		f.Order = "imported"

pkg/clean/gps.go

@@ -88,9 +88,13 @@ func GPSLatRange(lat float64, km uint) (latN, latS float32, err error) {
 		return 0, 0, fmt.Errorf("invalid latitude")
 	}
 
-	// Approximate range.
-	latN = gpsCeil(lat + geo.KmToDeg(km))
-	latS = gpsFloor(lat - geo.KmToDeg(km))
+	// Approximate range radius.
+	r := float64(km) * 0.75
+
+	// Approximate longitude range,
+	// see https://en.wikipedia.org/wiki/Decimal_degrees
+	latN = gpsCeil(lat + geo.Deg(r))
+	latS = gpsFloor(lat - geo.Deg(r))
 
 	if latN > 90 {
 		latN = 90
@@ -110,9 +114,13 @@ func GPSLngRange(lng float64, km uint) (lngE, lngW float32, err error) {
 		return 0, 0, fmt.Errorf("invalid longitude")
 	}
 
-	// Approximate range.
-	lngE = gpsCeil(lng + geo.KmToDeg(km))
-	lngW = gpsFloor(lng - geo.KmToDeg(km))
+	// Approximate range radius.
+	r := float64(km) * 0.75
+
+	// Approximate longitude range,
+	// see https://en.wikipedia.org/wiki/Decimal_degrees
+	lngE = gpsCeil(lng + geo.Deg(r))
+	lngW = gpsFloor(lng - geo.Deg(r))
 
 	if lngE > 180 {
 		lngE = 180

pkg/clean/gps_test.go

@@ -68,8 +68,8 @@ func TestGPSBounds(t *testing.T) {
 func TestGPSLatRange(t *testing.T) {
 	t.Run("Valid", func(t *testing.T) {
 		latNorth, latSouth, err := GPSLatRange(41.87760543823242, 2)
-		assert.Equal(t, float32(41.8958), latNorth)
-		assert.Equal(t, float32(41.8594), latSouth)
+		assert.Equal(t, float32(41.8913), latNorth)
+		assert.Equal(t, float32(41.8639), latSouth)
 		assert.NoError(t, err)
 	})
 	t.Run("Zero", func(t *testing.T) {
@@ -83,8 +83,8 @@ func TestGPSLatRange(t *testing.T) {
 func TestGPSLngRange(t *testing.T) {
 	t.Run("Valid", func(t *testing.T) {
 		lngEast, lngWest, err := GPSLngRange(-87.62521362304688, 2)
-		assert.Equal(t, float32(-87.6434), lngWest)
-		assert.Equal(t, float32(-87.607), lngEast)
+		assert.Equal(t, float32(-87.6389), lngWest)
+		assert.Equal(t, float32(-87.6116), lngEast)
 		assert.NoError(t, err)
 	})
 	t.Run("Zero", func(t *testing.T) {

pkg/geo/dist.go

@@ -10,9 +10,10 @@ const (
 	DefaultDist    uint = 2
 )
 
-// KmToDeg returns the approximate distance in decimal degrees.
-func KmToDeg(km uint) float64 {
-	return 0.009009009 * float64(km)
+// Deg returns the approximate distance in decimal degrees,
+// see https://en.wikipedia.org/wiki/Decimal_degrees.
+func Deg(km float64) float64 {
+	return 0.009009009 * km
 }
 
 // DegToRad converts a value from degrees to radians.

pkg/geo/dist_test.go

@@ -6,9 +6,9 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestKmToDeg(t *testing.T) {
+func TestDeg(t *testing.T) {
 	t.Run("10km", func(t *testing.T) {
-		assert.Equal(t, 0.09009009, KmToDeg(10))
+		assert.Equal(t, 0.09009009, Deg(10))
 	})
 }