Routes do not have elevation calculation

[vojtabohm]

Problem
When a GPX contains only routes (<rte>/<rtept>) and no tracks, gpx.length_3d() and gpx.get_uphill_downhill() return 0, despite elevation and points being present. This is because the built-in computations operate on tracks/segments, not routes.

Expected
Non-zero distance and elevation gain are computed for route-only files when elevation is present.

Proposed solution (non-breaking)
Provide a helper/utility (or mention in docs) to convert routes to tracks so built-in computations work as expected.

def convert_routes_to_tracks(gpx: gpxpy.gpx.GPX):
    """Convert all routes to tracks (1 segment per route, 1:1 points)."""
    for route in list(gpx.routes):
        track = gpxpy.gpx.GPXTrack(name=route.name or "Unnamed Route")
        segment = gpxpy.gpx.GPXTrackSegment()
        for rp in route.points:
            segment.points.append(
                gpxpy.gpx.GPXTrackPoint(
                    rp.latitude,
                    rp.longitude,
                    elevation=rp.elevation,
                )
            )
        track.segments.append(segment)
        gpx.tracks.append(track)
    gpx.routes = []

I currently employ this solution in my code and I suspect @tkrajina does too in his own tool. Upon parsing, I convert all routes to tracks.

Why this helps

• After conversion, gpx.length_3d() and gpx.get_uphill_downhill() produce correct values without changing downstream code.
• Keeps behavior backward-compatible and leverages existing track-based computations.

Request
Consider adding a built-in converter (e.g., gpx.convert_routes_to_tracks()), or document this pattern clearly for users working with route-only GPX files.

I’m happy to submit a PR with this helper and a note in the docs.