#! /usr/bin/python
import sys
import xml.etree.cElementTree as ET

et = ET.parse(sys.argv[1])
last = 0; l = []
for e in et.findall('*/*/*/{http://www.topografix.com/GPX/1/1}ele'):
    alt = float(e.text)
    if alt < last - 200: # wrong value
        l.append(e)
        continue
    if l:
        delta = (alt - last)/(len(l) + 1)
        for e in l:
            last += delta
            e.text = '%.1f' % last
        l = []
    last = alt
ET.register_namespace('', 'http://www.topografix.com/GPX/1/1')
et.write(sys.argv[2], 'UTF-8')