Replace number attribute with a range of values when generating merge…

…d GPX

app.py

@@ -76,8 +76,8 @@ def post_merge_gpx_tracks():
             ]
         )
 
-    # The GPX driver requires the "number" column to be an integer, not a string
-    merged_tracks["number"] = pandas.to_numeric(merged_tracks["number"])
+    if output_format == "gpx":
+        merged_tracks["number"] = range(1, len(merged_tracks) + 1)
 
     with tempfile.TemporaryDirectory() as temp_dir:
         merged_file = str(Path(temp_dir) / f"merged.{extension}")

templates/merge-gpx-tracks.html

@@ -22,6 +22,11 @@
                     </label>
                 </div>
             {% endfor %}
+
+            <div class="alert alert-warning" role="alert">
+                Note: For GPX output the <code>number</code> attribute will be replaced with an incremental counter to
+                avoid missing or duplicate values.
+            </div>
         </div>
 
         <button type="submit" class="btn btn-primary">Merge Tracks</button>