From ac9e09893b118c90e4f1fca66cd9287cce3fd01f Mon Sep 17 00:00:00 2001 From: Nick Foster Date: Sun, 14 Oct 2012 22:34:50 -0700 Subject: [PATCH] CPR changes. Fixed a lot of the surface position errors. At least one bug still remains. --- python/cpr.py | 89 ++++++++++++++++++++++++++++++--------------------- 1 file changed, 52 insertions(+), 37 deletions(-) diff --git a/python/cpr.py b/python/cpr.py index 1d647dd..7c29013 100755 --- a/python/cpr.py +++ b/python/cpr.py @@ -28,12 +28,6 @@ from air_modes.exceptions import * latz = 15 -def nbits(surface): - if surface == 1: - return 19 - else: - return 17 - def nz(ctype): return 4 * latz - ctype @@ -49,9 +43,6 @@ def dlat(ctype, surface): else: return tmp / nzcalc -def nl_eo(declat_in, ctype): - return nl(declat_in) - ctype - def nl(declat_in): if abs(declat_in) >= 87.0: return 1.0 @@ -62,25 +53,23 @@ def dlon(declat_in, ctype, surface): tmp = 90.0 else: tmp = 360.0 - nlcalc = nl_eo(declat_in, ctype) + nlcalc = nl(declat_in)-ctype if nlcalc == 0: return tmp else: - return tmp / max(nlcalc, 1.0) + return tmp / nlcalc def decode_lat(enclat, ctype, my_lat, surface): tmp1 = dlat(ctype, surface) - tmp2 = float(enclat) / (2**nbits(surface)) + tmp2 = float(enclat) / (2**17) j = math.floor(my_lat/tmp1) + math.floor(0.5 + ((my_lat % tmp1) / tmp1) - tmp2) -# print "dlat gives " + "%.6f " % tmp1 + "with j = " + "%.6f " % j + " and tmp2 = " + "%.6f" % tmp2 + " given enclat " + "%x" % enclat return tmp1 * (j + tmp2) def decode_lon(declat, enclon, ctype, my_lon, surface): tmp1 = dlon(declat, ctype, surface) - tmp2 = float(enclon) / (2.0**nbits(surface)) + tmp2 = float(enclon) / (2**17) m = math.floor(my_lon / tmp1) + math.floor(0.5 + ((my_lon % tmp1) / tmp1) - tmp2) -# print "dlon gives " + "%.6f " % tmp1 + "with m = " + "%.6f " % m + " and tmp2 = " + "%.6f" % tmp2 + " given enclon " + "%x" % enclon return tmp1 * (m + tmp2) @@ -93,7 +82,11 @@ def cpr_resolve_local(my_location, encoded_location, ctype, surface): return [decoded_lat, decoded_lon] -def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): +def cpr_resolve_global(evenpos, oddpos, mypos, mostrecent, surface): + #cannot resolve surface positions unambiguously without knowing receiver position + if surface and mypos is None: + raise CPRNoPositionError + dlateven = dlat(0, surface) dlatodd = dlat(1, surface) @@ -114,7 +107,6 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): #This checks to see if the latitudes of the reports straddle a transition boundary #If so, you can't get a globally-resolvable location. if nl(rlateven) != nl(rlatodd): - #print "Boundary straddle!" raise CPRBoundaryStraddleError if mostrecent == 0: @@ -122,21 +114,41 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface): else: rlat = rlatodd + #disambiguate latitude + if surface: + if mypos[0] < 0: + rlat -= 90 + dl = dlon(rlat, mostrecent, surface) nlthing = nl(rlat) - ni = max(nlthing - mostrecent, 1) + ni = nlthing - mostrecent - m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/2**17)+0.5) #longitude index + #THIS COLLAPSES WHEN M IS NOT A FACTOR OF FOUR + m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*nlthing)/2**17)+0.5) #longitude index + if m%4: + print "IM GONNA DIE" + + print "DL: %f nlthing: %f ni: %f m: %f" % (dl, nlthing, ni, m) if mostrecent == 0: enclon = evenpos[1] else: enclon = oddpos[1] - rlon = dl * (((ni+m) % ni)+enclon/2**17) + rlon = dl * ((m % ni)+enclon/2**17) + if surface: + #longitudes need to be resolved to the nearest 90 degree segment to the receiver. + wat = mypos[1] + if wat < 0: + wat += 360 + print "mylon: %f mylon unwrapped: %f rlon raw: %f" % (mypos[1], wat, rlon) + zone = lambda lon: 90 * (int(lon) / 90) + rlon += (zone(wat) - zone(rlon)) + + #limit to (-180, 180) if rlon > 180: - rlon = rlon - 360.0 + rlon -= 360.0 return [rlat, rlon] @@ -199,8 +211,7 @@ class cpr_decoder: if (icao24 in self.evenlist) \ and (icao24 in self.oddlist): newer = (self.oddlist[icao24][2] - self.evenlist[icao24][2]) > 0 #figure out which report is newer - [decoded_lat, decoded_lon] = cpr_resolve_global(self.evenlist[icao24][0:2], self.oddlist[icao24][0:2], newer, surface) #do a global decode - + [decoded_lat, decoded_lon] = cpr_resolve_global(self.evenlist[icao24][0:2], self.oddlist[icao24][0:2], self.my_location, newer, surface) #do a global decode else: raise CPRNoPositionError @@ -223,11 +234,11 @@ def cpr_encode(lat, lon, ctype, surface): yz = math.floor(scalar * ((lat % dlati)/dlati) + 0.5) rlat = dlati * ((yz / scalar) + math.floor(lat / dlati)) - nleo = nl_eo(rlat, ctype) + nleo = nl(rlat)-ctype if nleo == 0: dloni = 360.0 else: - dloni = 360.0 / nl_eo(rlat, ctype) + dloni = 360.0 / nleo xz = math.floor(scalar * ((lon % dloni)/dloni) + 0.5) @@ -245,53 +256,57 @@ if __name__ == '__main__': #latitudes the corresponding error in longitude is greater bs = 0 + surface = True for i in range(0, rounds): - decoder = cpr_decoder(None) even_lat = random.uniform(-85, 85) - even_lon = random.uniform(-180,180) + even_lon = random.uniform(-180, 180) odd_lat = even_lat + 1e-2 odd_lon = min(even_lon + 1e-2, 180) + decoder = cpr_decoder([odd_lat, odd_lon]) #encode that position - (evenenclat, evenenclon) = cpr_encode(even_lat, even_lon, False, False) - (oddenclat, oddenclon) = cpr_encode(odd_lat, odd_lon, True, False) + (evenenclat, evenenclon) = cpr_encode(even_lat, even_lon, False, surface) + (oddenclat, oddenclon) = cpr_encode(odd_lat, odd_lon, True, surface) #perform a global decode icao = random.randint(0, 0xffffff) try: - evenpos = decoder.decode(icao, evenenclat, evenenclon, False, False) + evenpos = decoder.decode(icao, evenenclat, evenenclon, False, surface) #print "CPR global decode with only one report: %f %f" % (evenpos[0], evenpos[1]) raise Exception("CPR test failure: global decode with only one report") except CPRNoPositionError: pass try: - (odddeclat, odddeclon, rng, brg) = decoder.decode(icao, oddenclat, oddenclon, True, False) + (odddeclat, odddeclon, rng, brg) = decoder.decode(icao, oddenclat, oddenclon, True, surface) except CPRBoundaryStraddleError: bs += 1 continue except CPRNoPositionError: raise Exception("CPR test failure: no decode after even/odd inputs") - #print "Lat: %f Lon: %f" % (ac_lat, ac_lon) - if abs(odddeclat - odd_lat) > threshold or abs(odddeclon - odd_lon) > threshold: - print "odddeclat: %f odd_lat: %f" % (odddeclat, odd_lat) - print "odddeclon: %f odd_lon: %f" % (odddeclon, odd_lon) + print "F odddeclat: %f odd_lat: %f" % (odddeclat, odd_lat) + print "F odddeclon: %f odd_lon: %f" % (odddeclon, odd_lon) raise Exception("CPR test failure: global decode error greater than threshold") + else: + print "S odddeclat: %f odd_lat: %f" % (odddeclat, odd_lat) + print "S odddeclon: %f odd_lon: %f" % (odddeclon, odd_lon) nexteven_lat = odd_lat + 1e-2 nexteven_lon = min(odd_lon + 1e-2, 180) - (nexteven_enclat, nexteven_enclon) = cpr_encode(nexteven_lat, nexteven_lon, False, False) + (nexteven_enclat, nexteven_enclon) = cpr_encode(nexteven_lat, nexteven_lon, False, surface) try: - (evendeclat, evendeclon) = cpr_resolve_local([even_lat, even_lon], [nexteven_enclat, nexteven_enclon], False, False) + (evendeclat, evendeclon) = cpr_resolve_local([even_lat, even_lon], [nexteven_enclat, nexteven_enclon], False, surface) except CPRNoPositionError: raise Exception("CPR test failure: local decode failure to resolve") if abs(evendeclat - nexteven_lat) > threshold or abs(evendeclon - nexteven_lon) > threshold: + print "F evendeclat: %f nexteven_lat: %f evenlat: %f" % (evendeclat, nexteven_lat, even_lat) + print "F evendeclon: %f nexteven_lon: %f evenlon: %f" % (evendeclon, nexteven_lon, even_lon) raise Exception("CPR test failure: local decode error greater than threshold") print "CPR test successful. There were %i boundary straddles over %i rounds." % (bs, rounds)