--- a/README.md	Wed Aug 30 17:53:53 2017 +0200
+++ b/README.md	Fri Sep 01 15:23:33 2017 +0200
@@ -1,32 +1,39 @@
 # gpx_reduce_light
 
-* gpx_reduce.py is a version of the [original gpx_reduce][1] with no dependencies.
+* gpx_reduce.py is a modified version of the [original gpx_reduce][1] with no dependencies.
 
-    The [original version][1] depends on scipy, lxml, numpy and pylab.
-    Because the program only does some basic linear algebra, all these dependencies can be easily removed.
+    The original depends on *scipy, lxml, numpy* and *pylab* (which are heavy requirements).
+    However, these dependencies can be easily removed, because the program only does basic linear
+    algebra.
     This has two benefits:
 
     1. easy installation (nothing needed apart from python)
-    2. the program is considerably faster than the original.  
-        This is because the original uses a numpy array for each trackpoint which
-        incurs a large overhead for creating and for all subsequent little computations.
+    2. the program is considerably faster than the original.
+    
+    A stand alone windows executable (win32, 3 Mb) can be downloaded from <https://wim.vree.org/sporen/gpx.html>
 
-    The one disadvantage of removing all depecencies is that the plot option had to be removed.  
-    Usage example:
+    Usage example (see [original][1] for a better description):
 
         > gpx_reduce.py -d 2 -t 30 your_track.gpx
 
+    The disadvantage of removing all dependencies is that the plot option had to be removed.  
     I made a separate python script with one dependency for plotting tracks:
 
-* gpx_plot.py, a script to plot one or more tracks with "gnuplot".
+* gpx_plot.py, a script to plot one or more tracks with [gnuplot][3].
 
-    Gnuplot has to be installed and the path to the binary has to be changed in the code
-    to reflect your installation:
-
-        gnuPlotCmd = 'path/to/gnuplot'
+    Gnuplot has to be installed and if the path to the gnuplot executable is not */usr/bin/gnuplot*
+    you have to specify the path with the command line option *-g /path/to/gnuplot*
 
     Usage example that compares a reduced track with the original:
 
         > gpx_plot.py your_track.gpx your_track_reduced.gpx
+    
+    and with the -g option:
 
-[1]: https://github.com/Alezy80/gpx_reduce/
\ No newline at end of file
+        > gpx_plot.py -g /path/to/gnuplot your_track.gpx your_track_reduced.gpx
+    
+    A stand alone windows executable (win32, 3 Mb) can be downloaded from <https://wim.vree.org/sporen/gpx.html>
+    (does not include [gnuplot][3])
+
+[1]: https://github.com/Alezy80/gpx_reduce/
+[3]: https://sourceforge.net/projects/gnuplot/files/gnuplot/

--- a/gpx_plot.py	Wed Aug 30 17:53:53 2017 +0200
+++ b/gpx_plot.py	Fri Sep 01 15:23:33 2017 +0200
@@ -21,24 +21,26 @@
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 '''
 
-import datetime
-import sys
-import time
+import datetime, sys, os, time
 from math import *
 import xml.etree.ElementTree as etree
 from optparse import OptionParser
 
-# the path to the gnuplot binary
-gnuPlotCmd = 'gnuplot'
-
 parser = OptionParser('usage: %prog [options] input-file.gpx')
+parser.add_option('-g', action='store', type='string', dest='gnuplot',
+    default='/usr/bin/gnuplot', help='PATH to the gnuplot binary (or .exe)', metavar='PATH')
 (options, args) = parser.parse_args()
 
+# the path to the gnuplot binary
+gnuPlotCmd = options.gnuplot
+if not os.path.exists (gnuPlotCmd):
+    print gnuPlotCmd, 'does not exist'
+    parser.print_help ()
+    sys.exit ()
 
 if len(args) < 1:
-    parser.print_usage()
-    exit(2)
-
+    parser.print_help ()
+    sys.exit ()
 
 # use the WGS-84 ellipsoid
 rE = 6356752.314245 # earth's radius
@@ -94,8 +96,11 @@
     ntot = 0    # total number of trackpoints (sum of segments)
     
     # import xml data from files
+    if not os.path.exists (fname):
+        print fname, 'does not exist'
+        continue
     print 'opening file', fname
-    infile = open(fname)
+    infile = open (fname)
     tree = etree.parse(infile)
     infile.close()
 
@@ -161,7 +166,11 @@
     xmin -= dr
 
 from subprocess import Popen, PIPE
-plot = Popen ([gnuPlotCmd], stdin=PIPE, stdout=PIPE, stderr=PIPE)
+try:
+    plot = Popen ([gnuPlotCmd], stdin=PIPE, stdout=PIPE, stderr=PIPE)
+except Exception as e:
+    print e, 'while executing', gnuPlotCmd
+    sys.exit ()
 
 range = 'set xrange [%f:%f]\nset yrange [%f:%f]\n' % (xmin, xmax, ymin, ymax)
 plot.stdin.write (range)
@@ -172,4 +181,4 @@
 plot.stdin.write ("\n".join (data))
 plot.stdin.write ('\n')
 plot.stdin.flush ()
-raw_input ('druk')
+raw_input ('press enter to exit program')