From d18786b00028f73abf324c639cc362d2524445a2 Mon Sep 17 00:00:00 2001
From: rrr-marble <rrr@marble.lan>
Date: Sun, 19 Dec 2021 23:17:34 +0300
Subject: [PATCH] add: transform coordinates to decimal form

---
 util/import_photos.py | 39 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/util/import_photos.py b/util/import_photos.py
index 32a4065..401e750 100644
--- a/util/import_photos.py
+++ b/util/import_photos.py
@@ -6,9 +6,44 @@ import filetype
 from os import path, walk
 from sys import argv, stderr
 from shutil import move
+from fractions import Fraction
 import sqlite3
 
 
+def decimal_from_rational64u(dms: str):
+    """Convert coordinates from rational64u EXIF uses to represent
+    degrees, minutes, and seconds of a point to decimal format
+
+    General formula is
+    dec_degree = degreesNumerator / degreesDenominator
+                 + minutesNumerator / minutesDenominator / 60
+                 + secondsNumerator / secondsDenominator / 3600
+
+    https://en.wikipedia.org/wiki/Geographic_coordinate_conversion
+    https://gis.stackexchange.com/questions/136925/how-to-parse-exif-gps-information-to-lat-lng-decimal-numbers
+
+    >>> decimal_from_rational64u(dms="42/1, 18/1, 2914/100")
+    42.30809
+    """
+
+    # 1 split by comma
+    # 2 turn each into Fraction
+    # 3 zip fractions with their respective (degrees, minutes, seconds) denominator
+    # 4 divide the fraction
+    # 5 sum up the result
+    # 6 convert to decimal
+    # 7 round to 5th decimal point
+    return round(
+        float(
+            sum(
+                a / b
+                for (a, b) in zip((Fraction(f) for f in dms.split(",")), (1, 60, 3600))
+            )
+        ),
+        5,
+    )
+
+
 def process_pictures(source: str, dest_shrunk: str, dest_original: str):
     """Process images from the base directory in the first command line argument.
     Place the resized copies to dest_shrunk and
@@ -53,9 +88,9 @@ def process_pictures(source: str, dest_shrunk: str, dest_original: str):
                 "ResizedImage": path.join(dest_shrunk, filename),
                 "OriginalImage": path.join(dest_original, filename),
                 "DateTimeOriginal": exif["DateTimeOriginal"],  # Q: normalize it?
-                "GPSLatitude": exif["GPSLatitude"],
+                "GPSLatitude": decimal_from_rational64u(exif["GPSLatitude"]),
                 "GPSLatitudeRef": exif["GPSLatitudeRef"],
-                "GPSLongitude": exif["GPSLongitude"],
+                "GPSLongitude": decimal_from_rational64u(exif["GPSLongitude"]),
                 "GPSLongitudeRef": exif["GPSLongitudeRef"],
             }
         except KeyError as e: