Plot the altitude over the distance from GPX files

plot_altitude_gpx.py

import gpxpy
import matplotlib.pyplot as plt
import os
import re

from itertools import accumulate


size = 1.2
gpx_folderpath = "gpx/"


def parse_gpx_file(file_path):
    gpx_file = open(file_path, 'r')
    gpx = gpxpy.parse(gpx_file)

    latitudes = []
    longitudes = []
    altitudes = []
    distances = []

    previous_point = None

    for track in gpx.tracks:
        for segment in track.segments:
            for point in segment.points:
                latitudes.append(point.latitude)
                longitudes.append(point.longitude)
                altitudes.append(point.elevation)

                if previous_point:
                    distance = previous_point.distance_3d(point)
                    distances.append(distance)
                else:
                    distances.append(0)

                previous_point = point

    return latitudes, longitudes, altitudes, distances


def sort_key(file):
    num = re.search(r'(\d+)', file).group(1)
    num = num.replace('-', ' ')
    num = int(num) if num.isdigit() else 0
    return (num, file)

files = [f for f in os.listdir(gpx_folderpath) if os.path.isfile(os.path.join(gpx_folderpath, f))]
files.sort(key=sort_key)


altitudes, distances, distance_per_day = [], [], [0]
for filename in files:
    gpx_file_path = gpx_folderpath + filename
    _, _, altitudes_piece, distances_piece = parse_gpx_file(gpx_file_path)
    altitudes += altitudes_piece
    distances += [e/1000 for e in distances_piece]
    distance_per_day.append(sum(distances))

cumulative_distances = list(accumulate(distances))


plt.plot(cumulative_distances, altitudes)
for e in distance_per_day:
    plt.axvline(x = e, color = (245/255,99/255,88/255))
plt.xlabel('Distance (km)')
plt.ylabel('Altitude (m)')
plt.title('Altitude vs Distance')
plt.gcf().set_size_inches(60*size, 13*size)
plt.grid(True)
plt.savefig('out.png')
plt.show()