Interpolate missing positions in gpx

interpolategpx.py

import xml.etree.ElementTree as ET
import dateutil.parser
from datetime import timedelta

class Interpolate(object):
	def __init__(self, knownWpts):
		self.knownWpts = knownWpts[:]
		self.knownWpts.sort()

		#for wpt in self.knownWpts:
		#	print wpt

	def Predict(self, wpt):
		besti = None
		for i in range(len(self.knownWpts)-1):
			if wpt[0] >= self.knownWpts[i][0] and wpt[0] < self.knownWpts[i+1][0]:
				besti = i

		dt = self.knownWpts[besti+1][0] - self.knownWpts[besti][0]
		frac = (wpt[0] - self.knownWpts[besti][0]).total_seconds() / dt.total_seconds()
		lat1, lat2 = self.knownWpts[besti][1], self.knownWpts[besti+1][1]
		lon1, lon2 = self.knownWpts[besti][2], self.knownWpts[besti+1][2]

		latp = lat1 + frac * (lat2 - lat1)
		lonp = lon1 + frac * (lon2 - lon1)

		#dt2 = timedelta(seconds=frac * dt.total_seconds())

		return latp, lonp

if __name__=="__main__":
	
	tree = ET.parse('20171121wpts.gpx')
	root = tree.getroot()

	out = ET.Element("gpx")

	knownWpts = []
	unknownWpts = []

	for wpt in root:

		try:
			lat, lon = map(float, (wpt.attrib["lat"], wpt.attrib["lon"]))
		except ValueError:
			lat, lon = None, None

		timeNode = wpt.find("{http://www.topografix.com/GPX/1/0}time")
		nameNode = wpt.find("{http://www.topografix.com/GPX/1/0}name")
		nameText = None
		if nameNode is not None:
			nameText = nameNode.text 

		if timeNode is not None:
			timestamp = dateutil.parser.parse(timeNode.text)

			if lat is not None:
				knownWpts.append((timestamp, lat, lon, nameText))
			else:
				unknownWpts.append((timestamp, nameText))

	interpolate = Interpolate(knownWpts)

	for wpt in unknownWpts:

		lat, lon = interpolate.Predict(wpt)
		wptNode = ET.SubElement(out, 'wpt')
		wptNode.attrib["lat"] = str(lat)
		wptNode.attrib["lon"] = str(lon)
		wptName = ET.SubElement(wptNode, 'name')
		wptName.text = wpt[1]

	for wpt in knownWpts:

		wptNode = ET.SubElement(out, 'wpt')
		wptNode.attrib["lat"] = str(wpt[1])
		wptNode.attrib["lon"] = str(wpt[2])
		wptName = ET.SubElement(wptNode, 'name')
		wptName.text = wpt[3]

	fi = open("out.gpx", "wt")
	ET.ElementTree(out).write(fi, encoding="utf-8")
	fi.close()