252 lines
7.5 KiB
Python
252 lines
7.5 KiB
Python
#
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# Copyright 2010 Nick Foster
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#
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# This file is part of gr-air-modes
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#
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# gr-air-modes is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3, or (at your option)
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# any later version.
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#
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# gr-air-modes is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with gr-air-modes; see the file COPYING. If not, write to
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# the Free Software Foundation, Inc., 51 Franklin Street,
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# Boston, MA 02110-1301, USA.
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#
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#!/usr/bin/env python
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#from string import split, join
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#from math import pi, floor, cos, acos
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import math, time
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#this implements CPR position decoding.
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latz = 15
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def nbits(surface):
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return 17
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# if surface == 1:
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# return 19
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# else:
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# return 17
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def nz(ctype):
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return 4 * latz - ctype
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def dlat(ctype, surface):
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if surface == 1:
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tmp = 90.0
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else:
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tmp = 360.0
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nzcalc = nz(ctype)
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if nzcalc == 0:
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return tmp
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else:
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return tmp / nzcalc
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def nl_eo(declat_in, ctype):
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return nl(declat_in) - ctype
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def nl(declat_in):
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return math.floor( (2.0*math.pi) * pow(math.acos(1.0- (1.0-math.cos(math.pi/(2.0*latz))) / pow( math.cos( (math.pi/180.0)*abs(declat_in) ) ,2.0) ),-1.0))
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def dlon(declat_in, ctype, surface):
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if surface == 1:
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tmp = 90.0
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else:
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tmp = 360.0
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nlcalc = nl_eo(declat_in, ctype)
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if nlcalc == 0:
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return tmp
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else:
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return tmp / nlcalc
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def decode_lat(enclat, ctype, my_lat, surface):
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tmp1 = dlat(ctype, surface)
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tmp2 = float(enclat) / (2**nbits(surface))
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j = math.floor(my_lat/tmp1) + math.floor(0.5 + (mod(my_lat, tmp1) / tmp1) - tmp2)
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# print "dlat gives " + "%.6f " % tmp1 + "with j = " + "%.6f " % j + " and tmp2 = " + "%.6f" % tmp2 + " given enclat " + "%x" % enclat
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return tmp1 * (j + tmp2)
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def decode_lon(declat, enclon, ctype, my_lon, surface):
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tmp1 = dlon(declat, ctype, surface)
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tmp2 = float(enclon) / (2.0**nbits(surface))
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m = math.floor(my_lon / tmp1) + math.floor(0.5 + (mod(my_lon, tmp1) / tmp1) - tmp2)
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# print "dlon gives " + "%.6f " % tmp1 + "with m = " + "%.6f " % m + " and tmp2 = " + "%.6f" % tmp2 + " given enclon " + "%x" % enclon
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return tmp1 * (m + tmp2)
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def mod(a, b):
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if a < 0:
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a += 360.0
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return a - b * math.floor(a / b)
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def cpr_resolve_local(my_location, encoded_location, ctype, surface):
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[my_lat, my_lon] = my_location
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[enclat, enclon] = encoded_location
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decoded_lat = decode_lat(enclat, ctype, my_lat, surface)
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decoded_lon = decode_lon(decoded_lat, enclon, ctype, my_lon, surface)
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return [decoded_lat, decoded_lon]
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def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #ok this is considered working, tentatively
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dlateven = dlat(0, surface);
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dlatodd = dlat(1, surface);
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# print dlateven;
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# print dlatodd;
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evenpos = [float(evenpos[0]), float(evenpos[1])]
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oddpos = [float(oddpos[0]), float(oddpos[1])]
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#print "Even position: %x, %x\nOdd position: %x, %x" % (evenpos[0], evenpos[1], oddpos[0], oddpos[1],)
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j = math.floor(((59*evenpos[0] - 60*oddpos[0])/2**nbits(surface)) + 0.5) #latitude index
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#print "Latitude index: %i" % j #should be 6, getting 5?
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rlateven = dlateven * (mod(j, 60)+evenpos[0]/2**nbits(surface))
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rlatodd = dlatodd * (mod(j, 59)+ oddpos[0]/2**nbits(surface))
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#print "Rlateven: %f\nRlatodd: %f" % (rlateven, rlatodd,)
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if nl(rlateven) != nl(rlatodd):
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#print "Boundary straddle!"
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return (None, None,)
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if mostrecent == 0:
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rlat = rlateven
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else:
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rlat = rlatodd
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if rlat > 90:
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rlat = rlat - 180.0
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dl = dlon(rlat, mostrecent, surface)
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nlthing = nl(rlat)
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ni = nlthing - mostrecent
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#print "ni is %i" % ni
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m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/2**nbits(surface))+0.5) #longitude index, THIS LINE IS CORRECT
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#print "m is %f" % m #should be -16
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if mostrecent == 0:
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enclon = evenpos[1]
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else:
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enclon = oddpos[1]
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rlon = dl * (mod(ni+m, ni)+enclon/2**nbits(surface))
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if rlon > 180:
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rlon = rlon - 360.0
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return [rlat, rlon]
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#calculate range and bearing between two lat/lon points
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#should probably throw this in the mlat py somewhere or make another lib
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def range_bearing(loc_a, loc_b):
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[a_lat, a_lon] = loc_a
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[b_lat, b_lon] = loc_b
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esquared = (1/298.257223563)*(2-(1/298.257223563))
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earth_radius_mi = 3963.19059 * (math.pi / 180)
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delta_lat = b_lat - a_lat
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delta_lon = b_lon - a_lon
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avg_lat = (a_lat + b_lat) / 2.0
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R1 = earth_radius_mi*(1.0-esquared)/pow((1.0-esquared*pow(math.sin(avg_lat),2)),1.5)
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R2 = earth_radius_mi/math.sqrt(1.0-esquared*pow(math.sin(avg_lat),2))
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distance_North = R1*delta_lat
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distance_East = R2*math.cos(avg_lat)*delta_lon
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bearing = math.atan2(distance_East,distance_North) * (180.0 / math.pi)
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if bearing < 0.0:
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bearing += 360.0
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rnge = math.hypot(distance_East,distance_North)
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return [rnge, bearing]
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class cpr_decoder:
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def __init__(self, my_location):
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self.my_location = my_location
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self.lkplist = []
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self.evenlist = []
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self.oddlist = []
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def set_location(new_location):
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self.my_location = new_location
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def weed_poslists(self):
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for poslist in [self.lkplist, self.evenlist, self.oddlist]:
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for key, item in poslist.items():
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if time.time() - item[2] > 900:
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del poslist[key]
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def decode(icao24, encoded_lat, encoded_lon, cpr_format, surface):
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#def cpr_decode(my_location, icao24, encoded_lat, encoded_lon, cpr_format, evenlist, oddlist, lkplist, surface):
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#add the info to the position reports list for global decoding
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if cpr_format==1:
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oddlist[icao24] = [encoded_lat, encoded_lon, time.time()]
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else:
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evenlist[icao24] = [encoded_lat, encoded_lon, time.time()]
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[decoded_lat, decoded_lon] = [None, None]
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#okay, let's traverse the lists and weed out those entries that are older than 15 minutes, as they're unlikely to be useful.
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self.weed_poslists()
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if surface==1:
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validrange = 45
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else:
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validrange = 180
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if icao24 in self.lkplist:
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#do emitter-centered local decoding
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[decoded_lat, decoded_lon] = cpr_resolve_local(self.lkplist[icao24][0:2], [encoded_lat, encoded_lon], cpr_format, surface)
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self.lkplist[icao24] = [decoded_lat, decoded_lon, time.time()] #update the local position for next time
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elif ((icao24 in self.evenlist) and (icao24 in self.oddlist) and abs(self.evenlist[icao24][2] - self.oddlist[icao24][2]) < 10):
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# print "debug: valid even/odd positions, performing global decode."
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newer = (self.oddlist[icao24][2] - self.evenlist[icao24][2]) > 0 #figure out which report is newer
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[decoded_lat, decoded_lon] = cpr_resolve_global(self.evenlist[icao24][0:2], self.oddlist[icao24][0:2], newer, surface) #do a global decode
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if decoded_lat is not None:
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self.lkplist[icao24] = [decoded_lat, decoded_lon, time.time()]
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elif self.my_location is not None: #if we have a location, use it
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[local_lat, local_lon] = cpr_resolve_local(self.my_location, [encoded_lat, encoded_lon], cpr_format, surface) #try local decoding
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[rnge, bearing] = range_bearing(self.my_location, [local_lat, local_lon])
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if rnge < validrange: #if the local decoding can be guaranteed valid
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self.lkplist[icao24] = [local_lat, local_lon, time.time()] #update the local position for next time
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[decoded_lat, decoded_lon] = [local_lat, local_lon]
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#print "settled on position: %.6f, %.6f" % (decoded_lat, decoded_lon,)
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if decoded_lat is not None:
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[rnge, bearing] = range_bearing(self.my_location, [decoded_lat, decoded_lon])
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else:
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rnge = None
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bearing = None
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return [decoded_lat, decoded_lon, rnge, bearing]
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