From 039f7adbc63faae1314ca535d713c5789c816841 Mon Sep 17 00:00:00 2001
From: EtiennePelletier <etpelletier93@hotmail.com>
Date: Wed, 4 Nov 2020 20:41:21 -0500
Subject: [PATCH] Modify get_gps_coords util to handle tags in native Python

---
 exifread/utils.py | 64 +++++++++++++++++++++++++++++------------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/exifread/utils.py b/exifread/utils.py
index 2d11ffc..b87944f 100644
--- a/exifread/utils.py
+++ b/exifread/utils.py
@@ -3,6 +3,7 @@
 """
 
 from fractions import Fraction
+from typing import Tuple, Union
 
 
 def ord_(dta):
@@ -41,32 +42,47 @@ def make_string_uc(seq) -> str:
     return make_string(seq)
 
 
-def get_gps_coords(tags: dict) -> tuple:
-
-    lng_ref_tag_name = 'GPS GPSLongitudeRef'
-    lng_tag_name = 'GPS GPSLongitude'
-    lat_ref_tag_name = 'GPS GPSLatitudeRef'
-    lat_tag_name = 'GPS GPSLatitude'
-
-    # Check if these tags are present
-    gps_tags = [lng_ref_tag_name, lng_tag_name, lat_tag_name, lat_tag_name]
-    for tag in gps_tags:
-        if not tag in tags.keys():
-            return ()
-
-    lng_ref_val = tags[lng_ref_tag_name].values
-    lng_coord_val = [c.decimal() for c in tags[lng_tag_name].values]
-
-    lat_ref_val = tags[lat_ref_tag_name].values
-    lat_coord_val = [c.decimal() for c in tags[lat_tag_name].values]
-
-    lng_coord = sum([c/60**i for i, c in enumerate(lng_coord_val)])
-    lng_coord *= (-1) ** (lng_ref_val == 'W')
+def degrees_to_decimal(degrees: float, minutes: float, seconds: float) -> float:
+    """
+    Converts coordinates from a degrees minutes seconds format to a decimal degrees format.
+    Reference: https://en.wikipedia.org/wiki/Geographic_coordinate_conversion
+    """
+    return degrees + minutes/60 + seconds/3600
 
-    lat_coord = sum([c/60**i for i, c in enumerate(lat_coord_val)])
-    lat_coord *= (-1) ** (lat_ref_val == 'S')
 
-    return (lat_coord, lng_coord)
+def get_gps_coords(tags: dict) -> Union[Tuple[float, float], None]:
+    """
+    Extract tuple of latitude and longitude values in decimal degrees format from EXIF tags.
+    Return None if no GPS coordinates are found.
+    Handles regular and serialized Exif tags.
+    """
+    gps = {
+        'lat_coord': 'GPS GPSLatitude',
+        'lat_ref': 'GPS GPSLatitudeRef',
+        'lng_coord': 'GPS GPSLongitude',
+        'lng_ref': 'GPS GPSLongitudeRef'
+    }
+
+    # Verify if required keys are a subset of provided tags
+    if not set(gps.values()) <= tags.keys():
+        return None
+
+    # If tags have not been converted to native Python types, do it
+    if not isinstance(tags[gps['lat_coord']], list):
+        tags[gps['lat_coord']] = [c.decimal() for c in tags[gps['lat_coord']].values]
+        tags[gps['lng_coord']] = [c.decimal() for c in tags[gps['lng_coord']].values]
+        tags[gps['lat_ref']] = tags[gps['lat_ref']].values
+        tags[gps['lng_ref']] = tags[gps['lng_ref']].values
+
+    lat = degrees_to_decimal(*tags[gps['lat_coord']])
+    if tags[gps['lat_ref']] == 'S':
+        lat *= -1
+
+    lng = degrees_to_decimal(*tags[gps['lng_coord']])
+    if tags[gps['lng_ref']] == 'W':
+        lng *= -1
+
+    return lat, lng
 
 
 class Ratio(Fraction):