Reformat Exif tags for GPS position to be better understandable

libexif's formatting of these tags is not nice to read.
Reformatted are latitude and longitude values and their reference points.

https://bugzilla.gnome.org/show_bug.cgi?id=627185

origin commit:
https://gitlab.gnome.org/GNOME/eog/commit/3e4bc1a

1 files changed, 91 insertions, 3 deletions

diff --git a/src/eom-exif-details.c b/src/eom-exif-details.c
index 3281551..928e5f6 100644
--- a/src/eom-exif-details.c
+++ b/src/eom-exif-details.c
@@ -351,6 +351,94 @@ set_row_data (GtkTreeStore *store, char *path, char *parent, const char *attribu
 }
 
 #ifdef HAVE_EXIF
+
+static const char *
+eom_exif_entry_get_value (ExifEntry    *e,
+                          char         *buf,
+                          guint         n_buf)
+{
+	ExifByteOrder bo;
+
+	/* For now we only want to reformat some GPS values */
+	if (G_LIKELY (exif_entry_get_ifd (e) != EXIF_IFD_GPS))
+		return exif_entry_get_value (e, buf, n_buf);
+
+	bo = exif_data_get_byte_order (e->parent->parent);
+
+	/* Cast to number to avoid warnings about values not in enumeration */
+	switch ((guint16) e->tag) {
+		case EXIF_TAG_GPS_LATITUDE:
+		case EXIF_TAG_GPS_LONGITUDE:
+		{
+			gsize rational_size;
+			ExifRational r;
+			gfloat h = 0., m = 0.;
+
+
+			rational_size = exif_format_get_size (EXIF_FORMAT_RATIONAL);
+			if (G_UNLIKELY (e->components != 3 ||
+			    e->format != EXIF_FORMAT_RATIONAL))
+				return exif_entry_get_value (e, buf, n_buf);
+
+			r = exif_get_rational (e->data, bo);
+			if (r.denominator != 0)
+				h = (gfloat)r.numerator / r.denominator;
+
+			r = exif_get_rational (e->data + rational_size, bo);
+			if (r.denominator != 0)
+				m = (gfloat)r.numerator / (gfloat)r.denominator;
+
+			r = exif_get_rational (e->data + (2 * rational_size),
+					       bo);
+			if (r.numerator != 0 && r.denominator != 0) {
+				gfloat s;
+
+				s = (gfloat)r.numerator / (gfloat)r.denominator;
+				g_snprintf (buf, n_buf,
+					    "%.0f° %.0f' %.2f\"",
+					    h, m, s);
+			} else {
+				g_snprintf (buf, n_buf,
+					    "%.0f° %.2f'",
+					    h, m);
+			}
+
+			break;
+		}
+		case EXIF_TAG_GPS_LATITUDE_REF:
+		case EXIF_TAG_GPS_LONGITUDE_REF:
+		{
+			if (G_UNLIKELY (e->components != 2 ||
+			    e->format != EXIF_FORMAT_ASCII))
+				return exif_entry_get_value (e, buf, n_buf);
+
+			switch (e->data[0]) {
+			case 'N':
+				g_snprintf (buf, n_buf, "%s", _("North"));
+				break;
+			case 'E':
+				g_snprintf (buf, n_buf, "%s", _("East"));
+				break;
+			case 'W':
+				g_snprintf (buf, n_buf, "%s", _("West"));
+				break;
+			case 'S':
+				g_snprintf (buf, n_buf, "%s", _("South"));
+				break;
+			default:
+				return exif_entry_get_value (e, buf, n_buf);
+				break;
+			}
+			break;
+		}
+		default:
+			return exif_entry_get_value (e, buf, n_buf);
+			break;
+	}
+
+	return buf;
+}
+
 static void
 exif_entry_cb (ExifEntry *entry, gpointer data)
 {
@@ -374,7 +462,7 @@ exif_entry_cb (ExifEntry *entry, gpointer data)
 			      path,
 			      NULL,
 			      exif_tag_get_name_in_ifd (entry->tag, ifd),
-			      exif_entry_get_value (entry, b, sizeof(b)));
+			      eom_exif_entry_get_value (entry, b, sizeof(b)));
 	} else {
 
 		ExifMnoteData *mnote = (entry->tag == EXIF_TAG_MAKER_NOTE ?
@@ -406,8 +494,8 @@ exif_entry_cb (ExifEntry *entry, gpointer data)
 					     NULL,
 					     exif_categories[cat].path,
 					     exif_tag_get_name_in_ifd (entry->tag, ifd),
-					     exif_entry_get_value (entry, b,
-								   sizeof(b)));
+					     eom_exif_entry_get_value (entry, b,
+						                           sizeof(b)));
 
 			g_hash_table_insert (priv->id_path_hash,
 					     GINT_TO_POINTER (entry->tag),