tools: Import the gpxify program.

gpxify takes as input an recording retrieved from the GPS watch
and converts it to GPX format.

diff --git a/tools/gpxify b/tools/gpxify
new file mode 100755 (executable)
index 0000000..08c24e9
--- /dev/null
+++ b/tools/gpxify
@@ -0,0 +1,138 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2020 Tilman Sauerbeck (tilman at code-monkey de)
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+from datetime import datetime
+import struct
+import sys
+
+class Packet(object):
+    def __init__(self, unix_time, latitude, longitude):
+        self.unix_time = unix_time
+        self.latitude = latitude
+        self.longitude = longitude
+
+class PacketExtractor(object):
+    POINTS_PER_GROUP = 7
+    PADDING_BYTE = 0xff
+
+    def __init__(self, source):
+        self._source = source
+        self._unix_time = None
+        self._latitude = 0
+        self._longitude = 0
+        self._flags = 0
+        self._num_points = 0
+
+    def run(self):
+        header = self._source.read(5)
+
+        format_version, self._unix_time = struct.unpack('<BI', header)
+
+        if format_version != 1:
+            s = 'Unexpected format version {}'.format(format_version)
+            raise RuntimeError(s)
+
+        while True:
+            shift = self._num_points % PacketExtractor.POINTS_PER_GROUP
+            self._num_points += 1
+
+            if shift == 0:
+                self._flags = PacketExtractor.PADDING_BYTE
+
+                # Skip padding bytes.
+                while self._flags == PacketExtractor.PADDING_BYTE:
+                    self._flags, = struct.unpack('B', self._source.read(1))
+
+            if (self._flags & (1 << shift)) == 0:
+                d_time = 1
+            else:
+                d_time = self.read_uvarint()
+
+            # End-of-stream marker hit?
+            if d_time == 0xffffffff:
+                break
+
+            d_lat = self.read_svarint()
+            d_lon = self.read_svarint()
+
+            yield self.process_deltas(d_time, d_lat, d_lon)
+
+    def process_deltas(self, d_time, d_lat, d_lon):
+        self._unix_time += d_time
+        self._latitude += d_lat
+        self._longitude += d_lon
+
+        q = 600000.0
+
+        return Packet(self._unix_time, self._latitude / q, self._longitude / q)
+
+    def read_uvarint(self):
+        shift = 7
+        mask = 1 << shift
+        total_shift = 0
+        v = 0
+
+        while True:
+            b, = struct.unpack('B', self._source.read(1))
+
+            c = (b & (mask - 1))
+
+            v |= c << total_shift
+            total_shift += shift
+
+            if (b & mask) == 0:
+                break
+
+        return v
+
+    def read_svarint(self):
+        u = self.read_uvarint()
+
+        h = -(u & 1);
+        n = (u >> 1) ^ h;
+
+        return n
+
+if __name__ == '__main__':
+    filename = sys.argv[1]
+
+    with open(filename, 'rb') as f:
+        print('<?xml version="1.0"?>')
+        print('<gpx version="1.1" creator="gpxify">')
+        print('\t<trk>')
+        print('\t\t<name>{}</name>'.format(filename))
+        print('\t\t<number>{}</number>'.format(1))
+        print('\t\t<trkseg>')
+
+        for packet in PacketExtractor(f).run():
+            print('\t\t\t<trkpt lat="{:.8f}" lon="{:.8f}">'.format(
+                   packet.latitude, packet.longitude))
+
+            dt = datetime.utcfromtimestamp(packet.unix_time)
+
+            print(dt.strftime('\t\t\t\t<time>%Y-%m-%dT%H:%M:%SZ</time>'))
+            print('\t\t\t</trkpt>')
+
+        print('\t\t</trkseg>')
+        print('\t</trk>')
+        print('</gpx>')