136 lines
4.8 KiB
Python
136 lines
4.8 KiB
Python
def GET_FIELD_U(w, nb, pos):
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return (((w) >> (pos)) & ((1 << (nb)) - 1))
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def twos_complement(v, nb):
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sign = v >> (nb - 1)
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value = v
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if sign != 0:
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value = value - (1 << nb)
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return value
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def GET_FIELD_S(w, nb, pos):
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v = GET_FIELD_U(w, nb, pos)
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return twos_complement(v, nb)
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def extract_uint8(v, b):
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return (v >> (8 * (3 - b))) & 255
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def extract_int8(v, b):
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value = extract_uint8(v, b)
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if value > 127:
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value -= 256
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return value
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class EphemerisData:
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'''container for parsing a AID_EPH message
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Thanks to Sylvain Munaut <tnt@246tNt.com>
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http://cgit.osmocom.org/cgit/osmocom-lcs/tree/gps.c
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on of this parser
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See IS-GPS-200F.pdf Table 20-III for the field meanings, scaling factors and
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field widths
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'''
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def __init__(self, svId, subframes):
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from math import pow
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self.svId = svId
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week_no = GET_FIELD_U(subframes[1][2+0], 10, 20)
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# code_on_l2 = GET_FIELD_U(subframes[1][0], 2, 12)
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# sv_ura = GET_FIELD_U(subframes[1][0], 4, 8)
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# sv_health = GET_FIELD_U(subframes[1][0], 6, 2)
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# l2_p_flag = GET_FIELD_U(subframes[1][1], 1, 23)
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t_gd = GET_FIELD_S(subframes[1][2+4], 8, 6)
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iodc = (GET_FIELD_U(subframes[1][2+0], 2, 6) << 8) | GET_FIELD_U(
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subframes[1][2+5], 8, 22)
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t_oc = GET_FIELD_U(subframes[1][2+5], 16, 6)
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a_f2 = GET_FIELD_S(subframes[1][2+6], 8, 22)
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a_f1 = GET_FIELD_S(subframes[1][2+6], 16, 6)
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a_f0 = GET_FIELD_S(subframes[1][2+7], 22, 8)
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c_rs = GET_FIELD_S(subframes[2][2+0], 16, 6)
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delta_n = GET_FIELD_S(subframes[2][2+1], 16, 14)
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m_0 = (GET_FIELD_S(subframes[2][2+1], 8, 6) << 24) | GET_FIELD_U(
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subframes[2][2+2], 24, 6)
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c_uc = GET_FIELD_S(subframes[2][2+3], 16, 14)
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e = (GET_FIELD_U(subframes[2][2+3], 8, 6) << 24) | GET_FIELD_U(subframes[2][2+4], 24, 6)
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c_us = GET_FIELD_S(subframes[2][2+5], 16, 14)
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a_powhalf = (GET_FIELD_U(subframes[2][2+5], 8, 6) << 24) | GET_FIELD_U(
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subframes[2][2+6], 24, 6)
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t_oe = GET_FIELD_U(subframes[2][2+7], 16, 14)
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# fit_flag = GET_FIELD_U(subframes[2][7], 1, 7)
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c_ic = GET_FIELD_S(subframes[3][2+0], 16, 14)
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omega_0 = (GET_FIELD_S(subframes[3][2+0], 8, 6) << 24) | GET_FIELD_U(
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subframes[3][2+1], 24, 6)
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c_is = GET_FIELD_S(subframes[3][2+2], 16, 14)
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i_0 = (GET_FIELD_S(subframes[3][2+2], 8, 6) << 24) | GET_FIELD_U(
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subframes[3][2+3], 24, 6)
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c_rc = GET_FIELD_S(subframes[3][2+4], 16, 14)
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w = (GET_FIELD_S(subframes[3][2+4], 8, 6) << 24) | GET_FIELD_U(subframes[3][5], 24, 6)
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omega_dot = GET_FIELD_S(subframes[3][2+6], 24, 6)
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idot = GET_FIELD_S(subframes[3][2+7], 14, 8)
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self._rsvd1 = GET_FIELD_U(subframes[1][2+1], 23, 6)
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self._rsvd2 = GET_FIELD_U(subframes[1][2+2], 24, 6)
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self._rsvd3 = GET_FIELD_U(subframes[1][2+3], 24, 6)
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self._rsvd4 = GET_FIELD_U(subframes[1][2+4], 16, 14)
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self.aodo = GET_FIELD_U(subframes[2][2+7], 5, 8)
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# Definition of Pi used in the GPS coordinate system
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gpsPi = 3.1415926535898
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# now form variables in radians, meters and seconds etc
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self.Tgd = t_gd * pow(2, -31)
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self.A = pow(a_powhalf * pow(2, -19), 2.0)
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self.cic = c_ic * pow(2, -29)
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self.cis = c_is * pow(2, -29)
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self.crc = c_rc * pow(2, -5)
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self.crs = c_rs * pow(2, -5)
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self.cuc = c_uc * pow(2, -29)
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self.cus = c_us * pow(2, -29)
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self.deltaN = delta_n * pow(2, -43) * gpsPi
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self.ecc = e * pow(2, -33)
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self.i0 = i_0 * pow(2, -31) * gpsPi
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self.idot = idot * pow(2, -43) * gpsPi
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self.M0 = m_0 * pow(2, -31) * gpsPi
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self.omega = w * pow(2, -31) * gpsPi
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self.omega_dot = omega_dot * pow(2, -43) * gpsPi
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self.omega0 = omega_0 * pow(2, -31) * gpsPi
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self.toe = t_oe * pow(2, 4)
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# clock correction information
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self.toc = t_oc * pow(2, 4)
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self.gpsWeek = week_no
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self.af0 = a_f0 * pow(2, -31)
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self.af1 = a_f1 * pow(2, -43)
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self.af2 = a_f2 * pow(2, -55)
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iode1 = GET_FIELD_U(subframes[2][2+0], 8, 22)
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iode2 = GET_FIELD_U(subframes[3][2+7], 8, 22)
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self.valid = (iode1 == iode2) and (iode1 == (iodc & 0xff))
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self.iode = iode1
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if GET_FIELD_U(subframes[4][2+0], 6, 22) == 56 and \
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GET_FIELD_U(subframes[4][2+0], 2, 28) == 1 and \
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GET_FIELD_U(subframes[5][2+0], 2, 28) == 1:
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a0 = GET_FIELD_S(subframes[4][2], 8, 14) * pow(2, -30)
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a1 = GET_FIELD_S(subframes[4][2], 8, 6) * pow(2, -27)
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a2 = GET_FIELD_S(subframes[4][3], 8, 22) * pow(2, -24)
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a3 = GET_FIELD_S(subframes[4][3], 8, 14) * pow(2, -24)
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b0 = GET_FIELD_S(subframes[4][3], 8, 6) * pow(2, 11)
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b1 = GET_FIELD_S(subframes[4][4], 8, 22) * pow(2, 14)
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b2 = GET_FIELD_S(subframes[4][4], 8, 14) * pow(2, 16)
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b3 = GET_FIELD_S(subframes[4][4], 8, 6) * pow(2, 16)
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self.ionoAlpha = [a0, a1, a2, a3]
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self.ionoBeta = [b0, b1, b2, b3]
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self.ionoCoeffsValid = True
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else:
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self.ionoAlpha = []
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self.ionoBeta = []
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self.ionoCoeffsValid = False
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