CPR changes. Fixed a lot of the surface position errors. At least one bug still remains.
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Nick Foster
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3c8c60f57f
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@ -28,12 +28,6 @@ from air_modes.exceptions import *
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latz = 15
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def nbits(surface):
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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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@ -49,9 +43,6 @@ def dlat(ctype, surface):
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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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if abs(declat_in) >= 87.0:
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return 1.0
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@ -62,25 +53,23 @@ def dlon(declat_in, ctype, surface):
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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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nlcalc = nl(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 / max(nlcalc, 1.0)
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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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tmp2 = float(enclat) / (2**17)
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j = math.floor(my_lat/tmp1) + math.floor(0.5 + ((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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tmp2 = float(enclon) / (2**17)
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m = math.floor(my_lon / tmp1) + math.floor(0.5 + ((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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@ -93,7 +82,11 @@ def cpr_resolve_local(my_location, encoded_location, ctype, surface):
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return [decoded_lat, decoded_lon]
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def cpr_resolve_global(evenpos, oddpos, mostrecent, surface):
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def cpr_resolve_global(evenpos, oddpos, mypos, mostrecent, surface):
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#cannot resolve surface positions unambiguously without knowing receiver position
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if surface and mypos is None:
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raise CPRNoPositionError
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dlateven = dlat(0, surface)
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dlatodd = dlat(1, surface)
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@ -114,7 +107,6 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface):
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#This checks to see if the latitudes of the reports straddle a transition boundary
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#If so, you can't get a globally-resolvable location.
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if nl(rlateven) != nl(rlatodd):
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#print "Boundary straddle!"
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raise CPRBoundaryStraddleError
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if mostrecent == 0:
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@ -122,21 +114,41 @@ def cpr_resolve_global(evenpos, oddpos, mostrecent, surface):
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else:
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rlat = rlatodd
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#disambiguate latitude
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if surface:
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if mypos[0] < 0:
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rlat -= 90
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dl = dlon(rlat, mostrecent, surface)
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nlthing = nl(rlat)
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ni = max(nlthing - mostrecent, 1)
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ni = nlthing - mostrecent
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m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*(nlthing))/2**17)+0.5) #longitude index
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#THIS COLLAPSES WHEN M IS NOT A FACTOR OF FOUR
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m = math.floor(((evenpos[1]*(nlthing-1)-oddpos[1]*nlthing)/2**17)+0.5) #longitude index
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if m%4:
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print "IM GONNA DIE"
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print "DL: %f nlthing: %f ni: %f m: %f" % (dl, nlthing, ni, m)
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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 * (((ni+m) % ni)+enclon/2**17)
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rlon = dl * ((m % ni)+enclon/2**17)
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if surface:
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#longitudes need to be resolved to the nearest 90 degree segment to the receiver.
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wat = mypos[1]
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if wat < 0:
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wat += 360
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print "mylon: %f mylon unwrapped: %f rlon raw: %f" % (mypos[1], wat, rlon)
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zone = lambda lon: 90 * (int(lon) / 90)
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rlon += (zone(wat) - zone(rlon))
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#limit to (-180, 180)
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if rlon > 180:
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rlon = rlon - 360.0
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rlon -= 360.0
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return [rlat, rlon]
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@ -199,8 +211,7 @@ class cpr_decoder:
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if (icao24 in self.evenlist) \
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and (icao24 in self.oddlist):
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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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[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
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else:
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raise CPRNoPositionError
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@ -223,11 +234,11 @@ def cpr_encode(lat, lon, ctype, surface):
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yz = math.floor(scalar * ((lat % dlati)/dlati) + 0.5)
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rlat = dlati * ((yz / scalar) + math.floor(lat / dlati))
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nleo = nl_eo(rlat, ctype)
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nleo = nl(rlat)-ctype
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if nleo == 0:
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dloni = 360.0
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else:
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dloni = 360.0 / nl_eo(rlat, ctype)
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dloni = 360.0 / nleo
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xz = math.floor(scalar * ((lon % dloni)/dloni) + 0.5)
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@ -245,53 +256,57 @@ if __name__ == '__main__':
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#latitudes the corresponding error in longitude is greater
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bs = 0
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surface = True
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for i in range(0, rounds):
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decoder = cpr_decoder(None)
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even_lat = random.uniform(-85, 85)
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even_lon = random.uniform(-180, 180)
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odd_lat = even_lat + 1e-2
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odd_lon = min(even_lon + 1e-2, 180)
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decoder = cpr_decoder([odd_lat, odd_lon])
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#encode that position
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(evenenclat, evenenclon) = cpr_encode(even_lat, even_lon, False, False)
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(oddenclat, oddenclon) = cpr_encode(odd_lat, odd_lon, True, False)
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(evenenclat, evenenclon) = cpr_encode(even_lat, even_lon, False, surface)
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(oddenclat, oddenclon) = cpr_encode(odd_lat, odd_lon, True, surface)
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#perform a global decode
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icao = random.randint(0, 0xffffff)
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try:
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evenpos = decoder.decode(icao, evenenclat, evenenclon, False, False)
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evenpos = decoder.decode(icao, evenenclat, evenenclon, False, surface)
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#print "CPR global decode with only one report: %f %f" % (evenpos[0], evenpos[1])
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raise Exception("CPR test failure: global decode with only one report")
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except CPRNoPositionError:
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pass
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try:
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(odddeclat, odddeclon, rng, brg) = decoder.decode(icao, oddenclat, oddenclon, True, False)
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(odddeclat, odddeclon, rng, brg) = decoder.decode(icao, oddenclat, oddenclon, True, surface)
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except CPRBoundaryStraddleError:
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bs += 1
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continue
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except CPRNoPositionError:
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raise Exception("CPR test failure: no decode after even/odd inputs")
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#print "Lat: %f Lon: %f" % (ac_lat, ac_lon)
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if abs(odddeclat - odd_lat) > threshold or abs(odddeclon - odd_lon) > threshold:
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print "odddeclat: %f odd_lat: %f" % (odddeclat, odd_lat)
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print "odddeclon: %f odd_lon: %f" % (odddeclon, odd_lon)
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print "F odddeclat: %f odd_lat: %f" % (odddeclat, odd_lat)
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print "F odddeclon: %f odd_lon: %f" % (odddeclon, odd_lon)
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raise Exception("CPR test failure: global decode error greater than threshold")
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else:
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print "S odddeclat: %f odd_lat: %f" % (odddeclat, odd_lat)
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print "S odddeclon: %f odd_lon: %f" % (odddeclon, odd_lon)
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nexteven_lat = odd_lat + 1e-2
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nexteven_lon = min(odd_lon + 1e-2, 180)
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(nexteven_enclat, nexteven_enclon) = cpr_encode(nexteven_lat, nexteven_lon, False, False)
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(nexteven_enclat, nexteven_enclon) = cpr_encode(nexteven_lat, nexteven_lon, False, surface)
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try:
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(evendeclat, evendeclon) = cpr_resolve_local([even_lat, even_lon], [nexteven_enclat, nexteven_enclon], False, False)
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(evendeclat, evendeclon) = cpr_resolve_local([even_lat, even_lon], [nexteven_enclat, nexteven_enclon], False, surface)
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except CPRNoPositionError:
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raise Exception("CPR test failure: local decode failure to resolve")
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if abs(evendeclat - nexteven_lat) > threshold or abs(evendeclon - nexteven_lon) > threshold:
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print "F evendeclat: %f nexteven_lat: %f evenlat: %f" % (evendeclat, nexteven_lat, even_lat)
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print "F evendeclon: %f nexteven_lon: %f evenlon: %f" % (evendeclon, nexteven_lon, even_lon)
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raise Exception("CPR test failure: local decode error greater than threshold")
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print "CPR test successful. There were %i boundary straddles over %i rounds." % (bs, rounds)
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