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#!/usr/bin/env python
#
# gpsprobe -- collect send-cycle and performance statistics on a GPS
from math import *
import time, os
import gps, gpsd
class Baton:
"Ship progress indication to stdout or stserr, whichever isn't redirected."
def __init__(self, prompt, endmsg=None):
if os.isatty(1):
self.stream = sys.stdout
elif os.isatty(2):
self.stream = sys.stderr
else:
self.stream = None
if self.stream:
self.stream.write(prompt + "... \010")
self.stream.flush()
self.count = 0
self.endmsg = endmsg
self.time = time.time()
return
def twirl(self, ch=None):
if self.stream is None:
return
if ch:
self.stream.write(ch)
else:
self.stream.write("-/|\\"[self.count % 4])
self.stream.write("\010")
self.count = self.count + 1
self.stream.flush()
return
def end(self, msg=None):
if msg == None:
msg = self.endmsg
if self.stream:
self.stream.write("...(%2.2f sec) %s.\n" % (time.time() - self.time, msg))
return
triggers = {
"PRWIZCH": "# This GPS has a Rockwell Zodiac chipset.\n"
}
SIRF = "# This GPS probably has a SiRF-II chipset.\n"
GE301 = "# GPVTG format indicates NMEA version >= 3.01.\n"
if __name__ == '__main__':
import sys, getopt
fixes = []
# Process options
(options, arguments) = getopt.getopt(sys.argv[1:], "n:p:")
await = 100;
device="/dev/gps"
for (switch, val) in options:
if (switch == '-n'):
await = int(val)
elif (switch == '-p'):
device = val
intervals = {}
last_seen = {}
notifications = []
last_command = None
def roundoff(n):
# Round a time to hundredths of a second
return round(n*100) / 100.0
def register(trait):
if (trait) not in notifications:
notifications.append(trait)
def count(sentence):
global intervals, last_seen, last_command
baton.twirl()
# Toss out everything that doesn't look like well-formed NMEA
fields = sentence.split(",")
leader = fields[0]
if leader and leader[0] == '$':
leader = leader[1:]
else:
return
# Throw out everything but the leader in each GPGSV group
if leader == "GPGSV" and last_command == "GPGSV":
return
last_command = leader
# Record timings
now = time.time()
if not leader in intervals:
intervals[leader] = []
if leader in last_seen:
intervals[leader].append(roundoff(now - last_seen[leader]))
last_seen[leader] = now
# Watch for trigger strings
for string in triggers.keys():
if sentence.find(string) > -1:
register(triggers[string])
if leader == "GPVTG":
if fields[2] == 'T':
register(GE301)
else:
register("# GPVTG format indicates NMEA version < 3.01.\n")
if leader == "GPRMC":
if len(fields) > 12 and fields[12] in "ADEMSN":
register("# GPRMC format indicates NMEA version >= 2.3.\n")
else:
register("# GPRMC format indicates NMEA version < 2.3.\n")
try:
# Step one: Gather data
dev = gpsd.gpsd(device=device)
baton = Baton("Waiting for %s" % device)
while True:
baton.twirl()
try:
dev.activate()
break
except IOError, e:
time.sleep(1)
baton.end("acquired")
starttime = time.time()
dev.set_raw_hook(count)
sys.stderr.write("Gathering %d sentences will probably take about %d seconds.\n"%(await, await/3,))
baton = Baton("Looking for first fix", "done")
countdown = await
while countdown > 0:
status = dev.poll()
if status > 0:
if dev.status > gps.STATUS_NO_FIX and dev.mode > gps.MODE_NO_FIX:
if not fixes:
fixtime = (time.time()-starttime,)
baton.end("got it")
baton = Baton("Gathering fixes")
fixes.append((dev.latitude, dev.longitude))
countdown -= 1
if '.' in dev.utc:
register(SIRF)
baton.end()
del last_seen
# Step two: get command frequencies and the basic send cycle time
frequencies = {}
for (key, interval_list) in intervals.items():
frequencies[key] = {}
for interval in interval_list:
frequencies[key][interval] = frequencies[key].get(interval, 0) + 1
# filter out noise
for key in frequencies:
distribution = frequencies[key]
for interval in distribution.keys():
if distribution[interval] < 2:
del distribution[interval]
cycles = {}
for key in frequencies:
distribution = frequencies[key]
if len(frequencies[key].values()) == 1:
# The value is uniqe after filtering
cycles[key] = distribution.keys()[0]
else:
# Compute the mode
maxfreq = 0
for (interval, frequency) in distribution.items():
if distribution[interval] > maxfreq:
cycles[key] = interval
maxfreq = distribution[interval]
print "# This is a gnuplot script generated by gpsprobe at %s\n" % time.asctime()
print "# First fix in %f seconds." % fixtime
for key in cycles:
if len(frequencies[key].values()) == 1:
if cycles[key] == 1:
print "# %s: is emitted once a second." % key
else:
print "# %s: is emitted once every %d seconds." % (key, cycles[key])
else:
if cycles[key] == 1:
print "# %s: is probably emitted once a second." % key
else:
print "# %s: is probably emitted once every %d seconds." % (key, cycles[key])
sendcycle = min(*cycles.values())
if sendcycle == 1:
print "# Send cycle is once per second."
else:
print "# Send cycle is once per %d seconds." % sendcycle
# SiRF-II speaks 2.2, but with the 3.01 VTG format
if SIRF in notifications and GE301 in notifications:
notifications.remove(GE301)
# Step three: print out registered traits
sys.stdout.write("".join(notifications) + "\n")
# Step four: run an empirical check on uncertainty of position.
if len(fixes) == 0:
print "# No fixes collected, can't estimate accuracy."
else:
centroid = (sum(map(lambda x:x[0], fixes))/len(fixes), sum(map(lambda x:x[1], fixes))/len(fixes))
# Sort fixes by distance from centroid
def d(a, b): return sqrt((a[0] - b[0])**2 + (a[1] - b[1])**2)
fixes.sort(lambda x, y: cmp(d(centroid, x), d(centroid, y)))
# Compute CEP(50%)
cep_meters = gps.EarthDistance(centroid, fixes[len(fixes)/2])
# Convert fixes to offsets from centroid in meters
recentered = map(lambda fix: gps.MeterOffset(centroid, fix), fixes)
if centroid[0] < 0:
latstring = "%fS" % -centroid[0]
elif centroid[0] == 0:
latstring = "0"
else:
latstring = "%fN" % centroid[0]
if centroid[1] < 0:
lonstring = "%fW" % -centroid[1]
elif centroid[1] == 0:
lonstring = "0"
else:
lonstring = "%fE" % centroid[1]
sys.stdout.write("set autoscale\n")
sys.stdout.write('set key below\n')
sys.stdout.write('set key title "%s"\n' % time.asctime())
sys.stdout.write('set size ratio -1\n')
sys.stdout.write('set xlabel "Meters east from %s"\n' % lonstring)
sys.stdout.write('set ylabel "Meters north from %s"\n' % latstring)
sys.stdout.write('cep=%f\n' % d((0,0), recentered[len(fixes)/2]))
sys.stdout.write('set parametric\n')
sys.stdout.write('set trange [0:2*pi]\n')
sys.stdout.write('cx(t, r) = sin(t)*r\n')
sys.stdout.write('cy(t, r) = cos(t)*r\n')
sys.stdout.write('chlen = cep/20\n')
sys.stdout.write("set arrow from -chlen,0 to chlen,0 nohead\n")
sys.stdout.write("set arrow from 0,-chlen to 0,chlen nohead\n")
sys.stdout.write('plot "-" using 1:2 title "%d GPS fixes", cx(t, cep),cy(t, cep) title "CEP (50%%) = %f meters"\n' % (len(fixes), cep_meters))
sys.stdout.write("#\n")
sys.stdout.write("# Lat Lon\n")
for (lat, lon) in recentered:
sys.stdout.write(" %f %f\n" % (lat, lon))
sys.stdout.write("end\n")
except KeyboardInterrupt:
print "Aborted."
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