waytogpx.py

#!/usr/bin/env python3
"""Convert Openstreetmap Way to GPX format.

This Python script is derived from the following PERL script:
https://wiki.openstreetmap.org/wiki/Relations/Relations_to_GPX

Usage:

./waytogpx.py <way>

The result is a file way_<way>.gpx
"""

import argparse
from urllib.request import urlopen
import xml.etree.ElementTree as ET


gpx_template = """\
<?xml version="1.0" encoding="UTF-8"?>
<gpx
 version="1.0"
creator="GPSBabel - http://www.gpsbabel.org"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.topografix.com/GPX/1/0"
xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd">
<bounds minlat="{minlat}" minlon="{minlon}" maxlat="{maxlat}" maxlon="{maxlon}"/>
<trk><trkseg>
{waypoints}
</trkseg></trk>
</gpx>
"""


def main():
    """Run the main function."""
    # Parse command-line args
    parser = argparse.ArgumentParser("Convert OSM way to GPX.")
    parser.add_argument("way", type=int, help="Way to convert.")
    way = parser.parse_args().way

    # Download
    url = "https://www.openstreetmap.org/api/0.6/way/{}/full".format(way)
    print("Downloading", url)
    with urlopen(url) as f:
        string = f.read()
        root = ET.fromstring(string)

    # Build dictionary of nodes
    nodes = {}
    for el_node in root.findall("node"):
        nodes[el_node.attrib["id"]] = [
            float(el_node.attrib["lat"]),
            float(el_node.attrib["lon"])]

    # Build list of waypoints
    lats = []
    lons = []
    el_way = root.find("way")
    for el_nd in el_way.findall("nd"):
        lat, lon = nodes[el_nd.attrib["ref"]]
        lats.append(lat)
        lons.append(lon)

    # Write the gpx file
    fn_gpx = "way_{}.gpx".format(way)
    with open(fn_gpx, "w") as f:
        f.write(gpx_template.format(
            minlat=min(lats),
            maxlat=max(lats),
            minlon=min(lons),
            maxlon=max(lons),
            waypoints="\n".join(['<trkpt lat="{}" lon="{}" />'.format(
                lat, lon) for lat, lon in zip(lats, lons)])
        ))
    print("Written", fn_gpx)


if __name__ == '__main__':
    main()