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#!/usr/bin/env python
'''
fit best estimate of magnetometer offsets
'''
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__)), '..'))
from optparse import OptionParser
parser = OptionParser("magfit.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("--noise", type='float', default=0, help="noise to add")
parser.add_option("--mav10", action='store_true', default=False, help="Use MAVLink protocol 1.0")
(opts, args) = parser.parse_args()
if opts.mav10:
os.environ['MAVLINK10'] = '1'
import mavutil
from rotmat import Vector3
if len(args) < 1:
print("Usage: magfit.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 select_data(data):
ret = []
counts = {}
for d in data:
mag = d
key = "%u:%u:%u" % (mag.x/20,mag.y/20,mag.z/20)
if key in counts:
counts[key] += 1
else:
counts[key] = 1
if counts[key] < 3:
ret.append(d)
print(len(data), len(ret))
return ret
def radius(mag, offsets):
'''return radius give data point and offsets'''
return (mag + offsets).length()
def radius_cmp(a, b, offsets):
'''return radius give data point and offsets'''
diff = radius(a, offsets) - radius(b, offsets)
if diff > 0:
return 1
if diff < 0:
return -1
return 0
def sphere_error(p, data):
from scipy import sqrt
x,y,z,r = p
ofs = Vector3(x,y,z)
ret = []
for d in data:
mag = d
err = r - radius(mag, ofs)
ret.append(err)
return ret
def fit_data(data):
import numpy, scipy
from scipy import optimize
p0 = [0.0, 0.0, 0.0, 0.0]
p1, ier = optimize.leastsq(sphere_error, p0[:], args=(data))
if not ier in [1, 2, 3, 4]:
raise RuntimeError("Unable to find solution")
return (Vector3(p1[0], p1[1], p1[2]), p1[3])
def magfit(logfile):
'''find best magnetometer offset fit to a log file'''
print("Processing log %s" % filename)
mlog = mavutil.mavlink_connection(filename, notimestamps=opts.notimestamps)
data = []
last_t = 0
offsets = Vector3(0,0,0)
# now gather all the data
while True:
m = mlog.recv_match(condition=opts.condition)
if m is None:
break
if m.get_type() == "SENSOR_OFFSETS":
# update current offsets
offsets = Vector3(m.mag_ofs_x, m.mag_ofs_y, m.mag_ofs_z)
if m.get_type() == "RAW_IMU":
mag = Vector3(m.xmag, m.ymag, m.zmag)
# add data point after subtracting the current offsets
data.append(mag - offsets + noise())
print("Extracted %u data points" % len(data))
print("Current offsets: %s" % offsets)
data = select_data(data)
# do an initial fit with all data
(offsets, field_strength) = fit_data(data)
for count in range(3):
# sort the data by the radius
data.sort(lambda a,b : radius_cmp(a,b,offsets))
print("Fit %u : %s field_strength=%6.1f to %6.1f" % (
count, offsets,
radius(data[0], offsets), radius(data[-1], offsets)))
# discard outliers, keep the middle 3/4
data = data[len(data)/8:-len(data)/8]
# fit again
(offsets, field_strength) = fit_data(data)
print("Final : %s field_strength=%6.1f to %6.1f" % (
offsets,
radius(data[0], offsets), radius(data[-1], offsets)))
total = 0.0
for filename in args:
magfit(filename)
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