added rewrite_log.py example

examples/rewrite_log.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python
+'''
+example of rewriting a log with changed values
+
+this can be useful when wanting to replay a log with different values
+'''
+
+import os
+from argparse import ArgumentParser
+from progress.bar import Bar
+import time
+import struct
+import sys
+
+parser = ArgumentParser(description=__doc__)
+
+parser.add_argument("login")
+parser.add_argument("logout")
+
+args = parser.parse_args()
+
+from pymavlink import mavutil
+from pymavlink import DFReader
+import struct
+
+print("Opening %s" % args.login)
+login = mavutil.mavlink_connection(args.login)
+output = open(args.logout, mode='wb')
+
+def write_message(m):
+    mtype = m.get_type()
+    buf = bytearray(m.get_msgbuf())
+    if mtype == 'RRLT' and m.Idx == 2:
+        # fix beacon location
+        buf2 = buf[:3] + struct.pack("<ffiiiIB", m.Range, m.Uncertainty, int(-35.28230025*1e7), int(149.00661081*1e7), 58400, m.TS, m.Idx)
+        if len(buf2) != len(buf):
+            print("Buffer length error", m)
+            sys.exit(1)
+        buf = buf2
+    output.write(buf)
+
+bar = Bar('Processing log', max=100)
+
+pct = 0
+
+while True:
+    m = login.recv_msg()
+    write_message(m)
+
+    new_pct = (login.offset * 100) // login.data_len
+    if new_pct != pct:
+        bar.next()
+        pct = new_pct