gnss_models module

Model GNSS measurements and measurement corrections.

Functions to generate expected measurements, simulate noisy mesurements, and estimate pseudorange corrections (clock corrections, ionospheric and tropospheric delays) for given receiver states and time.

gnss_models._calculate_iono_delay(gps_millis, iono_params, rx_ecef, ephem=None, sv_posvel=None, constellation='gps')

Calculate the ionospheric delay in pseudorange using the Klobuchar model Section 5.3.2 [1].

Parameters:

• gps_millis (int) – Time at which measurements are needed, measured in milliseconds since start of GPS epoch [ms].

• iono_params (np.ndarray) – Ionospheric atmospheric delay parameters for Klobuchar model, passed in 2x4 array, use None if not available.

• rx_ecef (np.ndarray) – 3x1 receiver position in ECEF frame of reference [m], use None if not available.

• ephem (gnss_lib_py.navdata.navdata.NavData) – Satellite ephemeris parameters for measurement SVs, use None if using satellite positions instead.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Precomputed positions of satellites corresponding to the input gps_millis, set to None if not available.

• constellation (string) – Constellation used for the ionospheric parameters addition.

Returns:

iono_delay – Estimated delay caused by the ionosphere [m].

Return type:

np.ndarray

Notes

Based on code written by J. Makela. AE 456, Global Navigation Sat Systems, University of Illinois Urbana-Champaign. Fall 2017

References

[1]

Misra, P. and Enge, P, “Global Positioning System: Signals, Measurements, and Performance.” 2nd Edition, Ganga-Jamuna Press, 2006.

gnss_models._calculate_tropo_delay(gps_millis, rx_ecef, ephem=None, sv_posvel=None)

Calculate tropospheric delay

Parameters:

• gps_millis (int) – Time at which measurements are needed, measured in milliseconds since start of GPS epoch [ms].

• rx_ecef (np.ndarray) – 3x1 array of ECEF rx_pos position [m].

• ephem (gnss_lib_py.navdata.navdata.NavData) – Satellite ephemeris parameters for measurement SVs.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Precomputed positions of satellites, set to None if not available.

Returns:

tropo_delay – Tropospheric corrections to pseudorange measurements [m].

Return type:

np.ndarray

Notes

Based on code written by J. Makela. AE 456, Global Navigation Sat Systems, University of Illinois Urbana-Champaign. Fall 2017

gnss_models._extract_state_variables(state)

Extract position, velocity and clock bias terms from state.

Parameters:

state (gnss_lib_py.navdata.navdata.NavData) – NavData containing state values i.e. 3D position, 3D velocity, receiver clock bias and receiver clock drift rate at which measurements will be simulated.

Returns:

• rx_ecef (np.ndarray) – 3x1 Receiver 3D ECEF position [m].

• rx_v_ecef (np.ndarray) – 3x1 Receiver 3D ECEF velocity.

• clk_bias (float) – Receiver clock bais [m].

• clk_drift (float) – Receiver clock drift [m/s].

gnss_models.add_measures(measurements, state_estimate, ephemeris_path='/home/docs/checkouts/readthedocs.org/user_builds/gnss-lib-py/checkouts/latest/docs/source/data/ephemeris', iono_params=None, pseudorange=True, doppler=True, corrections=True, delta_t_dec=-2)

Estimate measurements and add to given navdata with rx measures.

Given measurements that were received, containing time, GNSS ID and SV ID, computes estimated pseudorange and doppler measurements and adds them to the input navdata.

If the input navdata does not contain SV positions and velocities, which are required to estimate measurements, they are added to the navdata as well.

Must contain rows: * gps_millis * gnss_id * sv_id

To use previously computed SV states, provide following rows: * x_sv_m * y_sv_m * z_sv_m * vx_sv_mps * vy_sv_mps * vz_sv_mps

To estimate the expected measurements, the receiver state is needed. This state is stored in state_estimate and must contain the following rows * x_rx*_m * y_rx*_m * z_rx*_m * vx_rx*_mps * vy_rx*_mps * vz_rx*_mps

Parameters:

• measurements (gnss_lib_py.navdata.navdata.NavData) – Received measurements for which SV states are required. Must contain gps_millis, gnss_id, and sv_id fields.

• state_estimate (gnss_lib_py.navdata.navdata.NavData) – Estimate for receiver states — ECEF x, y, and z positions in meters, ECEF x, y, and z velocities in meters, clock bias in meters, and the clock drift in meters per second — stored in a NavData instance.

• ephemeris_path (string or path-like) – Location where ephemeris files are stored. Files will be downloaded if they don’t exist for the given date and constellation.

• iono_params (np.ndarray) – Parameters to calculate the ionospheric delay in pseudoranges.

• pseudorange (bool) – Flag on whether pseudoranges are to be calculated and used or not.

• doppler (bool) – Flag on whether doppler measurements are to be calculated and used or not.

• corrections (bool) – Flag on whether pseudorange corrections are to be calculated and used or not.

• delta_t_dec (int) – Decimal places after which times are considered as belonging to the same discrete time interval.

Notes

In some cases, such as when using derived versions of the collected data from the Google Decimeter Challenge, the measurements contain state estimates in the same data structure as the received measurements. In such a case, a separate state_estimate can be generated using the particular class’ method for generating a separate state_estimate.

gnss_models.calculate_pseudorange_corr(gps_millis, state=None, ephem=None, sv_posvel=None, iono_params=None)

Incorporate corrections in measurements.

Incorporate clock corrections (relativistic and polynomial), tropospheric and ionospheric atmospheric delay corrections.

Parameters:

• gps_millis (int) – Time at which measurements are needed, measured in milliseconds since start of GPS epoch [ms].

• state (gnss_lib_py.navdata.navdata.NavData) – NavData containing state values i.e. 3D position, 3D velocity, receiver clock bias and receiver clock drift rate at which measurements will be simulated.

• ephem (gnss_lib_py.navdata.navdata.NavData) – Satellite ephemeris parameters for measurement SVs, use None if using satellite positions instead.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Precomputed positions of satellites corresponding to the input gps_millis, set to None if not available.

• iono_params (np.ndarray) – Ionospheric atmospheric delay parameters for Klobuchar model, passed in 2x4 array, use None if not available.

Returns:

• tropo_delay (np.ndarray) – Estimated delay caused by the troposhere [m].

• iono_delay (np.ndarray) – Estimated delay caused by the ionosphere [m].

Notes

Based on code written by J. Makela. AE 456, Global Navigation Sat Systems, University of Illinois Urbana-Champaign. Fall 2017

gnss_models.expected_measures(gps_millis, state, ephem=None, sv_posvel=None)

Compute expected pseudoranges and doppler measurements given receiver states.

Parameters:

• gps_millis (int) – Time at which measurements are needed, measured in milliseconds since start of GPS epoch [ms].

• state (gnss_lib_py.navdata.navdata.NavData) – NavData instance containing state i.e. 3D position, 3D velocity, receiver clock bias and receiver clock drift rate at which measurements have to be simulated. Must be a single state (single column)

• ephem (gnss_lib_py.navdata.navdata.NavData) – NavData instance containing satellite ephemeris parameters for a particular time of ephemeris, use None if not available and using position directly.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Precomputed positions of satellites (if available).

Returns:

• measurements (gnss_lib_py.navdata.navdata.NavData) – Pseudorange (label: prange) and doppler (label: doppler) measurements with satellite SV. Also contains SVs and gps_tow at which the measurements are simulated.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Satellite positions and velocities (same as input if provided).

gnss_models.simulate_measures(gps_millis, state, noise_dict=None, ephem=None, sv_posvel=None, rng=None, el_mask=5.0)

Simulate GNSS pseudoranges and doppler measurements given receiver state.

Measurements are simulated by finding satellites visible from the given position (in state), computing the expected pseudorange and doppler measurements for those satellites, corresponding to the given state, and adding Gaussian noise to these expected measurements.

Parameters:

• gps_millis (int) – Time at which measurements are needed, measured in milliseconds since start of GPS epoch [ms].

• state (gnss_lib_py.navdata.navdata.NavData) – NavData instance containing state i.e. 3D position, 3D velocity, receiver clock bias and receiver clock drift rate at which measurements have to be simulated. Must be a single state (single column)

• noise_dict (dict) – Dictionary with pseudorange (‘prange_sigma’) and doppler noise (‘doppler_sigma’) standard deviation values in [m] and [m/s]. If None, uses default values prange_sigma=6 and doppler_sigma=1.

• ephem (gnss_lib_py.navdata.navdata.NavData) – NavData instance containing satellite ephemeris parameters for a particular time of ephemeris. Use None if not available and using SV positions directly instead.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Precomputed positions of satellites, set to None if not available.

• rng (np.random.Generator) – A random number generator for sampling random noise values.

• el_mask (float) – The elevation mask above which satellites are considered visible from the given receiver position. Only visible sate.

Returns:

• measurements (gnss_lib_py.navdata.navdata.NavData) – Pseudorange (label: prange) and doppler (label: doppler) measurements with satellite SV. Gaussian noise is added to expected measurements to simulate stochasticity.

• sv_posvel (gnss_lib_py.navdata.navdata.NavData) – Satellite positions and velocities (same as input if provided).