Parse a GPX file and add extra locations by interpolation. This allows you to slow down a simulated route in Xcode/iOS Simulator.

gistfile1.py

#!/usr/bin/python

# Interpolate GPX waypoints to slow a simulated route down.

import itertools
import sys
import xml.etree.ElementTree as ET

def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = itertools.tee(iterable)
    next(b, None)
    return itertools.izip(a, b)

def add_points(tree, count):
  root = tree.getroot()
	newroot = ET.Element('gpx')
	for c0, c1 in pairwise(root):
		c0lat = float(c0.attrib["lat"])
		c1lat = float(c1.attrib["lat"])
		c0lon = float(c0.attrib["lon"])
		c1lon = float(c1.attrib["lon"])
		latdiff = c1lat - c0lat
		londiff = c1lon - c0lon

		latstep = latdiff / (count + 1)
		lonstep = londiff / (count + 1)
		ET.SubElement(newroot, "wpt", c0.attrib)
		for i in range(1, count + 1):
			sublat = c0lat + (i * latstep)
			sublon = c0lon + (i * lonstep)
			subelem = ET.SubElement(newroot, "wpt", { "lat": str(sublat), "lon": str(sublon) })
	ET.SubElement(newroot, "wpt", root[-1].attrib)

	newtree = ET.ElementTree(newroot)
	newtree.write(sys.stdout)

if __name__ == '__main__':
	# args: filename, additional point count
	tree = ET.parse(sys.argv[1])
	add_points(tree, int(sys.argv[2]))

Very useful, thanks. However I think there's an indentation problem line 16?

Looks good, but how do you use it?