diff -r 5467c893d121 -r f93786d4f68e gpx_reduce.py
--- a/gpx_reduce.py	Sun Aug 20 21:59:58 2017 +0200
+++ b/gpx_reduce.py	Mon Aug 21 14:07:37 2017 +0200
@@ -31,10 +31,10 @@
 import datetime
 import sys
 import time
-import numpy as sc
+import numpy as np
 import numpy.linalg as la
 from math import *
-from lxml import etree
+import xml.etree.ElementTree as etree
 from optparse import OptionParser
 
 
@@ -86,7 +86,7 @@
 def distance(p1_, pm_, p2_, ele_weight=1.0):
     # returns distance of pm from line between p1 and p2
 
-    p1, pm, p2 = sc.array(p1_), sc.array(pm_), sc.array(p2_)
+    p1, pm, p2 = np.array(p1_), np.array(pm_), np.array(p2_)
     h1, hm, h2 = la.norm(p1), la.norm(pm), la.norm(p2)
     if ele_weight != 1.0 and min(h1, hm, h2) > 0.0:
         hmean = (h1 + hm + h2) / 3.0
@@ -100,7 +100,7 @@
         return la.norm(vm)
     linem = line / linel
     
-    position = sc.dot(vm, linem) / linel
+    position = np.dot(vm, linem) / linel
     if position < 0.0:
         return la.norm(vm)
     elif position > 1.0:
@@ -181,8 +181,8 @@
         imin = None
         costmin = float('inf')
         for i1 in reversed(range(i2)):
-            p1 = sc.array(points[i1]['p'])
-            p2 = sc.array(points[i2]['p'])
+            p1 = np.array(points[i1]['p'])
+            p2 = np.array(points[i2]['p'])
             seglength = la.norm(p2 - p1)
             
             # estimate speed between p1 and p2
@@ -216,7 +216,7 @@
             distances_squared = []
             # iterate all medium points between i1 and i2
             for im in range(i1+1, i2):
-                pm = sc.array(points[im]['p'])
+                pm = np.array(points[im]['p'])
                 d = distance(p1, pm, p2, options.ele_weight)
                 if (d <= options.max_dist):
                     d_sq = (d / options.max_dist) ** 2
@@ -227,10 +227,10 @@
                     i1_i2_segment_valid = False
                 
                     # check if connection to any further point i1 is impossible
-                    d1 = sc.dot(p1 - p2, p1 - p2)
-                    d2 = sc.dot(pm - p2, pm - p2)
+                    d1 = np.dot(p1 - p2, p1 - p2)
+                    d2 = np.dot(pm - p2, pm - p2)
                     dd = options.max_dist ** 2
-                    d1d2 = sc.dot(p1 - p2, pm - p2)
+                    d1d2 = np.dot(p1 - p2, pm - p2)
                     # formula from cosines of point separation angle and cone-opening angles around points
                     if (d1 > dd and d2 > dd and (d1d2 + dd)**2 < (d2 - dd) * (d1 - dd)):
                         lower_i1_possible = False
@@ -257,13 +257,13 @@
                 # add a penalty for kinks
                 if options.bend > 0.:
                     if points[i1]['prev'] != -1:
-                        p0 = sc.array(points[points[i1]['prev']]['p'])
+                        p0 = np.array(points[points[i1]['prev']]['p'])
                         v0 = p1 - p0
                         v1 = p2 - p1
                         if la.norm(v0) > 0. and la.norm(v1) > 0.:
                             v0 /= la.norm(v0)
                             v1 /= la.norm(v1)
-                            kink = (1.0 - sc.dot(v0, v1)) / 2.0
+                            kink = (1.0 - np.dot(v0, v1)) / 2.0
                             penalties[i1] += options.bend * kink
         
         # find best predecessor
@@ -310,15 +310,14 @@
     # import xml data from files
     print 'opening file', fname
     infile = open(fname)
-    
     tree = etree.parse(infile)
     infile.close()
+
     gpx = tree.getroot()
-    if gpx.nsmap.has_key(None):
-        nsmap = '{' + gpx.nsmap[None] + '}'
-    else:
-        nsmap = ''
-    
+    nsurl = gpx.tag.split ('}')[0][1:]  # == 'http://www.topografix.com/GPX/1/1'
+    etree.register_namespace('', nsurl) # default namespace -> xmlns:.... in the output
+    nsmap = '{' + nsurl + '}'           # prefix for all tags in the tree
+
     # extract data from xml
     for trkseg in gpx.findall('.//' + nsmap + 'trkseg'):
         trkpts = trkseg.findall(nsmap + 'trkpt')
@@ -357,7 +356,7 @@
         # delete certain points from original data
         delete_pnums = [i for i in range(n) if i not in final_pnums]
         for i in reversed(delete_pnums):
-            del trkseg[trkseg.index(trkpts[i])]
+            trkseg.remove (trkpts[i])
         
         # save reduced trackseg for plotting
         if options.plot:
@@ -374,12 +373,10 @@
     else:
         ofname = fname + '_reduced.gpx'
     outfile = open(ofname, 'w')
-    outfile.write(etree.tostring(tree, xml_declaration=True,
-        pretty_print=True, encoding='utf-8'))
+    tree.write (outfile, encoding="utf-8", xml_declaration=True, default_namespace=None, method="xml")
     outfile.close()
     print 'modified copy written to', ofname
-    
-    
+
     # plot result to screen
     if options.plot:
         import pylab as pl