Adding altitude support to exif parser

Author: Rudde

MetadataExtractor.Tests/Data/ABOVE_SEA_LEVEL.jpg

@@ -52,6 +52,28 @@ public void GeoLocation()
             Assert.Equal(-1.9141666666666666, geoLocation!.Longitude);
         }
 
+        [Fact]
+        public void GeoLocationWithAltitude()
+        {
+            var metadata = ImageMetadataReader.ReadMetadata("Data/ABOVE_SEA_LEVEL.jpg");
+            var gpsDirectory = metadata.OfType<GpsDirectory>().First();
+            var geoLocation = gpsDirectory.GetGeoLocation();
+            Assert.NotNull(geoLocation);
+            Assert.True(geoLocation.Altitude > 1);
+        }
+
+        [Fact]
+        public void GetLocationWithAltitudeBelowSeaLevel()
+        {
+            var metadata = ImageMetadataReader.ReadMetadata("Data/BELOW_SEA_LEVEL.JPG");
+            var gpsDirectory = metadata.OfType<GpsDirectory>().First();
+            var geoLocation = gpsDirectory.GetGeoLocation();
+
+            Assert.NotNull(geoLocation);
+
+            Assert.True(geoLocation.Altitude < -1);
+        }
+
         [Fact]
         public void GpsDate()
         {

MetadataExtractor.Tests/Data/BELOW_SEA_LEVEL.JPG

@@ -163,8 +163,10 @@ public GpsDirectory() : base(_tagNameMap)
         {
             var latitudes = this.GetRationalArray(TagLatitude);
             var longitudes = this.GetRationalArray(TagLongitude);
+            bool hasAltitude = this.TryGetRational(TagAltitude, out var altitude);
             var latitudeRef = this.GetString(TagLatitudeRef);
             var longitudeRef = this.GetString(TagLongitudeRef);
+            bool hasAltitudeRef = this.TryGetByte(TagAltitudeRef, out var altitudeRef);
 
             // Make sure we have the required values
             if (latitudes is null || latitudes.Length != 3)
@@ -183,7 +185,17 @@ public GpsDirectory() : base(_tagNameMap)
             if (lat == null || lon == null)
                 return null;
 
-            return new GeoLocation((double)lat, (double)lon);
+            double? alt = null;
+
+            if (hasAltitude)
+            {
+                alt = altitude.ToDouble();
+
+                if (hasAltitudeRef && altitudeRef == 0x01) // Invert value when ref i 1, indicates that the value is below sea level
+                    alt = -1.0 * alt;
+            }
+
+            return new GeoLocation((double)lat, (double)lon, alt);
         }
 
         /// <summary>

MetadataExtractor.Tests/Formats/Exif/ExifDirectoryTest.cs

@@ -19,10 +19,12 @@ public sealed class GeoLocation
         /// </summary>
         /// <param name="latitude">the latitude, in degrees</param>
         /// <param name="longitude">the longitude, in degrees</param>
-        public GeoLocation(double latitude, double longitude)
+        /// <param name="altitude">the altitude, in meters</param>
+        public GeoLocation(double latitude, double longitude, double? altitude)
         {
             Latitude = latitude;
             Longitude = longitude;
+            Altitude = altitude;
         }
 
         /// <value>the latitudinal angle of this location, in degrees.</value>
@@ -31,6 +33,9 @@ public GeoLocation(double latitude, double longitude)
         /// <value>the longitudinal angle of this location, in degrees.</value>
         public double Longitude { get; }
 
+        /// <value>the altitude of this location, in meters.</value>
+        public double? Altitude { get; }
+
         /// <value>true, if both latitude and longitude are equal to zero</value>
         public bool IsZero => Latitude == 0 && Longitude == 0;