GNSS Constants

import gnss_lib_py as glp

Standard values for constants required to process GNSS measurements are available in utils/constants.py. These constant values are as recommended by Interface Control Documents for constellations or by dataset specific documentation.

To use any of these constants, you can refer to them as glp.CONSTANT. For example, to use the speed of light use:

print(f'The speed of light is {glp.C} m/s')

The speed of light is 299792458.0 m/s

For more control and to prevent accidentally loading other values or methods, you can also import the constants module and access values from it directly

from gnss_lib_py.utils import constants as consts
print(f'The speed of light is {consts.C} m/s')

The speed of light is 299792458.0 m/s

A list of all available constants has been rendered below for easy reference

from IPython.display import Code
import os
parent_directory = os.path.split(os.getcwd())[0]
consts_path = os.path.join(os.path.split(glp.__file__)[0], 'utils/constants.py')

Code(filename=consts_path, language='python')

"""Constants for GPS navigation and coordinate transforms.

Based on the UIUC ECE 456 implementation [1]_.

References
----------
.. [1] Makela, Jonathan, ECE 456, Global Nav Satellite Systems,
   Fall 2017. University of Illinois Urbana-Champaign. Coding Assignments.
.. [2] International GNSS Service (IGS), RINEX Working Group and Radio
   Technical Commission for Maritime Servies Special Committee. RINEX
   Version 3.04. http://acc.igs.org/misc/rinex304.pdf
.. [3] https://developer.android.com/reference/android/location/GnssStatus#constants_1
.. [4] https://developer.android.com/reference/android/location/GnssMeasurement#getCodeType()
.. [5] https://sys.qzss.go.jp/dod/en/constellation.html

"""

__authors__ = "Ashwin Kanhere"
__date__ = "13 July 2021"

from datetime import datetime, timezone
from numpy import sqrt


A = 6378137.
"""float : Semi-major axis (radius) of the Earth [m]."""

B = 6356752.3145
"""float : Semi-minor axis (radius) of the Earth [m]."""

E = sqrt(1.-(B**2)/(A**2)) # 0.08181919035596
"""float : Eccentricity of the shape (not orbit) of the Earth."""

E1SQ = 6.69437999014 * 0.001
"""float : First esscentricity squared of Earth (not orbit)."""

E2SQ = 6.73949674228 * 0.001
"""float : Second eccentricity squared of Earth (not orbit)."""

LAT_ACC_THRESH = 1.57e-6
""" float : 10 meter latitude accuracy."""

MU_EARTH = 398600.5e9
"""float : :math:`G*M_E`, the "gravitational constant" for orbital
motion about the Earth [m^3/s^2]."""

OMEGA_E_DOT = 7.2921151467e-5
"""float : The sidereal rotation rate of the Earth (WGS-84) [rad/s]."""

C = 299792458.
"""float : Speed of light [m/s]."""

F = -4.442807633e-10
"""float : Relativistic correction term [s/m^(1/2)]."""

F1 = 1.57542e9
"""float : GPS L1 frequency [Hz]."""

F2 = 1.22760e9
"""float : GPS L2 frequency [Hz]."""

T_TRANS = 70*0.001
"""float : Average time taken for signal transmission from GPS sats to
receivers."""

GRAV = -9.80665
"""float : Acceleration due to gravity ENU frame of reference [m/s]."""

WEEKSEC = 604800
""" int : Number of seconds in a week [s]."""

GPS_EPOCH_0 = datetime(1980, 1, 6, 0, 0, 0, 0, tzinfo=timezone.utc)
""" datetime.datetime: Starting time for GPS epoch"""

MILLIS_PER_DAY = 86400000

TROPO_DELAY_C1 = 2.47
"""float : First coefficient of simplified tropospheric delay model developed in [1]_."""

TROPO_DELAY_C2 = 0.0121
"""float : Second coefficient of simplified tropospheric delay model developed in [1]_."""

TROPO_DELAY_C3 = 1.33e-4
"""float : Third coefficient of simplified tropospheric delay model developed in [1]_."""

CONSTELLATION_CHARS = {'G' : 'gps',
                       'R' : 'glonass',
                       'S' : 'sbas',
                       'C' : 'beidou',
                       'E' : 'galileo',
                       'J' : 'qzss',
                       'I' : 'irnss',
                       }
"""dict : Satellite System identifier from Rinex specification p13 in [2]_."""

CONSTELLATION_ANDROID = {1 : 'gps',
                         3 : 'glonass',
                         2 : 'sbas',
                         5 : 'beidou',
                         6 : 'galileo',
                         4 : 'qzss',
                         7 : 'irnss',
                         0 : 'unknown',
                         }
"""dict : Satellite System identifier from GNSSStatus specification [3]_."""

CODE_TYPE_ANDROID = {
                     'gps' : {
                              'C' : "l1",
                              'Q' : "l5",
                              'X' : "l5",
                             },
                     'glonass' : {
                              'C' : "l1",
                             },
                     'qzss' : {
                              'C' : "l1",
                              'X' : "l5",
                             },
                     'galileo' : {
                              'C' : "e1",
                              'X' : "e5a",
                              'Q' : "e5a",
                             },
                     'beidou' : {
                              'I' : "b1",
                              'X' : "l5",
                             },
                    }
"""dict : GNSS code type identifier from GnssMeasurement specification [4]_."""

QZSS_PRN_SVN = {193 : 1,
                194 : 2,
                199 : 3,
                195 : 4,
                196 : 5,
               }
"""dict : Translation from PRN to SVN for the QZSS constellation [5]_."""