1 files changed, 145 insertions, 0 deletions
diff --git a/mavlink/share/pyshared/pymavlink/examples/magfit_delta.py b/mavlink/share/pyshared/pymavlink/examples/magfit_delta.py
new file mode 100644
index 000000000..87d2dbb7f
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+++ b/mavlink/share/pyshared/pymavlink/examples/magfit_delta.py
@@ -0,0 +1,145 @@
+#!/usr/bin/env python
+
+'''
+fit best estimate of magnetometer offsets using the algorithm from
+Bill Premerlani
+'''
+
+import sys, time, os, math
+
+# allow import from the parent directory, where mavlink.py is
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.realpath(__file__)), '..'))
+
+# command line option handling
+from optparse import OptionParser
+parser = OptionParser("magfit_delta.py [options]")
+parser.add_option("--no-timestamps",dest="notimestamps", action='store_true', help="Log doesn't have timestamps")
+parser.add_option("--condition",dest="condition", default=None, help="select packets by condition")
+parser.add_option("--mav10", action='store_true', default=False, help="Use MAVLink protocol 1.0")
+parser.add_option("--verbose", action='store_true', default=False, help="verbose offset output")
+parser.add_option("--gain", type='float', default=0.01, help="algorithm gain")
+parser.add_option("--noise", type='float', default=0, help="noise to add")
+parser.add_option("--max-change", type='float', default=10, help="max step change")
+parser.add_option("--min-diff", type='float', default=50, help="min mag vector delta")
+parser.add_option("--history", type='int', default=20, help="how many points to keep")
+parser.add_option("--repeat", type='int', default=1, help="number of repeats through the data")
+
+(opts, args) = parser.parse_args()
+
+if opts.mav10:
+    os.environ['MAVLINK10'] = '1'
+import mavutil
+from rotmat import Vector3, Matrix3
+
+if len(args) < 1:
+    print("Usage: magfit_delta.py [options] <LOGFILE...>")
+    sys.exit(1)
+
+def noise():
+    '''a noise vector'''
+    from random import gauss
+    v = Vector3(gauss(0, 1), gauss(0, 1), gauss(0, 1))
+    v.normalize()
+    return v * opts.noise
+
+def find_offsets(data, ofs):
+    '''find mag offsets by applying Bills "offsets revisited" algorithm
+       on the data
+
+       This is an implementation of the algorithm from:
+          http://gentlenav.googlecode.com/files/MagnetometerOffsetNullingRevisited.pdf
+       '''
+
+    # a limit on the maximum change in each step
+    max_change = opts.max_change
+
+    # the gain factor for the algorithm
+    gain = opts.gain
+
+    data2 = []
+    for d in data:
+        d = d.copy() + noise()
+        d.x = float(int(d.x + 0.5))
+        d.y = float(int(d.y + 0.5))
+        d.z = float(int(d.z + 0.5))
+        data2.append(d)
+    data = data2
+
+    history_idx = 0
+    mag_history = data[0:opts.history]
+    
+    for i in range(opts.history, len(data)):
+        B1 = mag_history[history_idx] + ofs
+        B2 = data[i] + ofs
+        
+        diff = B2 - B1
+        diff_length = diff.length()
+        if diff_length <= opts.min_diff:
+            # the mag vector hasn't changed enough - we don't get any
+            # information from this
+            history_idx = (history_idx+1) % opts.history
+            continue
+
+        mag_history[history_idx] = data[i]
+        history_idx = (history_idx+1) % opts.history
+
+        # equation 6 of Bills paper
+        delta = diff * (gain * (B2.length() - B1.length()) / diff_length)
+
+        # limit the change from any one reading. This is to prevent
+        # single crazy readings from throwing off the offsets for a long
+        # time
+        delta_length = delta.length()
+        if max_change != 0 and delta_length > max_change:
+            delta *= max_change / delta_length
+
+        # set the new offsets
+        ofs = ofs - delta
+
+        if opts.verbose:
+            print ofs
+    return ofs
+
+
+def magfit(logfile):
+    '''find best magnetometer offset fit to a log file'''
+
+    print("Processing log %s" % filename)
+
+    # open the log file
+    mlog = mavutil.mavlink_connection(filename, notimestamps=opts.notimestamps)
+
+    data = []
+    mag = None
+    offsets = Vector3(0,0,0)
+    
+    # now gather all the data
+    while True:
+        # get the next MAVLink message in the log
+        m = mlog.recv_match(condition=opts.condition)
+        if m is None:
+            break
+        if m.get_type() == "SENSOR_OFFSETS":
+            # update offsets that were used during this flight
+            offsets = Vector3(m.mag_ofs_x, m.mag_ofs_y, m.mag_ofs_z)
+        if m.get_type() == "RAW_IMU" and offsets != None:
+            # extract one mag vector, removing the offsets that were
+            # used during that flight to get the raw sensor values
+            mag = Vector3(m.xmag, m.ymag, m.zmag) - offsets
+            data.append(mag)
+
+    print("Extracted %u data points" % len(data))
+    print("Current offsets: %s" % offsets)
+
+    # run the fitting algorithm
+    ofs = offsets
+    ofs = Vector3(0,0,0)
+    for r in range(opts.repeat):
+        ofs = find_offsets(data, ofs)
+        print('Loop %u offsets %s' % (r, ofs))
+        sys.stdout.flush()
+    print("New offsets: %s" % ofs)
+
+total = 0.0
+for filename in args:
+    magfit(filename)