`CentroidingIdeal`#

class CentroidingIdeal(name: str, camera: Camera, sigma: ArrayWUnits = None, state_definition: list = None, sequence_definition: list = None)#

Bases: Measurement

Models the optical ideal centroiding measurement model.

Simulates centroiding measurements via a line-of-sight unit vector towards the target using a pinhole camera model.

The image-plane coordinates \((u, v)\) of a target at inertial position \(\mathbf{r}\) are

\[\begin{split}\begin{pmatrix}u\\v\end{pmatrix} = \frac{f}{(\mathbf{R}\,\hat{\boldsymbol{\ell}})_z} \begin{pmatrix} (\mathbf{R}\,\hat{\boldsymbol{\ell}})_x \\ (\mathbf{R}\,\hat{\boldsymbol{\ell}})_y \end{pmatrix}\end{split}\]

where \(f\) is the focal length, \(\mathbf{R}\) is the camera rotation matrix, and \(\hat{\boldsymbol{\ell}}\) is the unit line-of-sight vector.

Parameters:

name (str) – Name of the measurement model.
camera (Camera) – Camera object from scarabaeus.
sigma (ArrayWUnits, optional) – Measurement standard deviation for both xy directions in image plane. Defaults to None.
state_definition (list, optional) – StateVector definition list. Defaults to None.
sequence_definition (list, optional) – Sequence definition list. Defaults to None.

Raises:

RuntimeError – If the units extracted from the measurements are not consistent.
RuntimeError – If neither an EpochArray nor start/end Epochs are provided.

See also

scarabaeus.Measurement: Abstract base class for all measurement models.

References

“A Tutorial on Horizon-Based Optical Navigation and Attitude Determination with Space Imaging Systems”, John A. Christian, IEEE-Access, Vol. 9, 19819-19853, 2021.

Attributes:

camera: The camera object taking measurements.
instrument: The instrument.
name: The name of the Centroiding model.
sequence_definition: The sequence definition
sigma: The standard deviation of the measurements.
state_definition: The state vector definition.

Methods

`compute_partials`(target, epoch_array, frame)	Stacks together measurement _partials for an epoch array at different epochs.
`computed_measurements`(target, epoch_array, ...)	Computes the optical navigation measurement for a given target at a specific epoch.
`generate_measurement_dataset`(dataset_name, ...)	Generates a MeasurementDataSet object that can be used by filters downstream.
`observed_measurements`(file_name, meas_name)	Load centroiding measurements from a .json file.
`residuals`(observed_meas, computed_meas)	Generates the measurement model's residuals given observed and computed ArrayWFrames.
`set_image_epochs`(image_epochs)	Enable per-image centroid biases.
`set_image_index`(mapping)	Directly assign a pre-built `{epoch_value: image_index}` mapping (or None to disable).
`update_reference_state`(state_vector)	Call this once per iteration (before generate_measurement_dataset). The model will pull: - meas_bias_ideal_* (as ArrayWUnits) - gs_delta_location_ECEF_* (as ArrayWFrame) for this instrument (matching spice_id).
`write_observed_measurements`(target, ...)	Generates synthetic measurements and write them as a .json file.

compute_partials(target: Spacecraft, epoch_array: EpochArray, frame: Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER)) → list#

Stacks together measurement _partials for an epoch array at different epochs.

Parameters:

target (Spacecraft) – The target spacecraft.
epoch_array (EpochArray) – The epochs.
frame (Frame, optional) – The reference frame. Defaults to a J2000 Frame object.

Returns:

_partials – A list with all the _partials evaluated at different epochs in the epoch_array.

Return type:

list

computed_measurements(target: Body, epoch_array: EpochArray = None, epoch_start: EpochArray = None, epoch_end: EpochArray = None, tstep: float = 1.0, frame: Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER), noisy: bool = False, image_epochs: list | None = None) → ArrayWFrame#

Computes the optical navigation measurement for a given target at a specific epoch.

Parameters:

target (Body) – The target body to image.
epoch_array (EpochArray, optional) – Array of epochs at which to compute the measurement. Defaults to None.
epoch_start (EpochArray, optional) – Start epoch when building the array internally. Defaults to None.
epoch_end (EpochArray, optional) – End epoch when building the array internally. Defaults to None.
tstep (float, optional) – Time step [s] when building the array internally. Defaults to 1.
frame (Frame, optional) – Reference frame for the computation. Defaults to J2000.
noisy (bool, optional) – When True, adds Gaussian noise scaled by sigma. Defaults to False.

Returns:

comp_meas – The computed measurement as an array with units of inverse radians.

Return type:

ArrayWUnits

generate_measurement_dataset(dataset_name: str, target: Body, observed_meas: tuple | list | None = None, epochs: EpochArray | None = None, frame: Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER), noisy: bool = False) → list[MeasurementDataSet]#

Generates a MeasurementDataSet object that can be used by filters downstream.

Parameters:

dataset_name (str) – The name of the MeasurementDataSet.
target (Spacecraft) – The target spacecraft.
epoch_list (EpochArray, optional) – The epochs. Defaults to None.
epoch_start (EpochArray, optional) – The starting epoch. Defaults to None.
epoch_end (EpochArray, optional) – The end epoch. Defaults to None.
tstep (int, optional) – The integration timestep. Defaults to 1.
observed_measurements (list, optional) – The observed measurements. Defaults to None.
frame (Frame, optional) – The reference frame. Defaults to a J2000 Frame object.
noisy (bool, optional) – Indicates if noise is added to the measurements or not. Defaults to False.

Returns:

mds_list – A list of MeasurementDataSet objects representing the measurements with their key properties to be used by a filter.

Return type:

list[MeasurementDataSet]

:raises If the observed_meas list is only made by 3 elements`, it throws an error because it needs the 4th element in the list for the indices of :py:class:`the outlier_flag:

Notes

The MeasurementDataSet output is generated in 6 steps:

Computed measurements
Partials
Residuals
Sigmas
Outlier flag
Pack everything in a list
Pack the list in a MeasurementDataSet object

observed_measurements(file_name, meas_name: str = 'meas_ideal', units=None, frame: Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER), image_epochs: list | None = None)#

Load centroiding measurements from a .json file.

image_epochslist[float], optional: Ordered list of observation epoch values, one per image. Must be provided when the state vector contains a stacked centroid_bias_<suffix> entry (dim > 2).

residuals(observed_meas: ArrayWFrame, computed_meas: ArrayWFrame) → ArrayWFrame#

Generates the measurement model’s residuals given observed and computed ArrayWFrames.

Parameters:

observed_meas (ArrayWFrame) – The observed measurements values (O).
computed_meas (ArrayWFrame) – The computed measurements values (C).

Returns:

residuals – AWF with the residual O-C.

Return type:

ArrayWFrame

set_image_epochs(image_epochs: list | None)#

Enable per-image centroid biases.

Parameters:: image_epochs (list[float] | None) – Ordered list of observation epoch values, one per image. Image index equals the position in the list. Pass None to revert to global-bias mode.

set_image_index(mapping: dict | None)#: Directly assign a pre-built {epoch_value: image_index} mapping (or None to disable).

update_reference_state(state_vector: StateArray)#

Call this once per iteration (before generate_measurement_dataset). The model will pull:

meas_bias_ideal_* (as ArrayWUnits)

gs_delta_location_ECEF_* (as ArrayWFrame)

for this instrument (matching spice_id).

write_observed_measurements(target: Spacecraft, epoch_array: EpochArray = None, epoch_start: EpochArray = None, epoch_end: EpochArray = None, tstep: float = 1, frame: Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER), noisy: bool = False, file_name: str = 'ideal_measurement', check_visibility: bool = False, elevation_mask: float = 10.0, folder_path_override: str = None) → None#

Generates synthetic measurements and write them as a .json file. The input of this method encapsulate the ones needed for the “computed_meas” method in each measurement model class.

Parameters:

target (Spacecraft) – The target spacecraft for which the range measurement is to be computed.
epoch_array (EpochArray, optional) – An array of epochs (times) at which the range measurements should be computed. If provided, overrides epoch_start, epoch_end, and tstep.
epoch_start (EpochArray, optional) – The starting epoch for the range measurement computations. Required if epoch_array is not provided.
epoch_end (EpochArray, optional) – The ending epoch for the range measurement computations. Required if epoch_array is not provided.
tstep (float, optional) – The time step, in seconds, between consecutive range measurements. If epoch_array is not provided. Defaults to 1 second.
frame (Frame , optional) – The reference frame in which the range computation is performed. Defaults to None.
noisy (bool , optional) – Whether to add noise to the computed range measurement. Defaults to False.
file_name (str, optional) – The filename of the JSON in which the measurement is saved, Defaults to 'ideal_measurement'.
check_visibility (bool, optional) – When True, epochs where the instrument cannot observe the target are removed before generating measurements. The specific check is instrument-dependent: GroundStation uses an elevation-angle test; Camera uses a FOV projection test. Defaults to False.
elevation_mask (float, optional) – Minimum elevation angle in degrees used by the GroundStation visibility check. Ignored for Camera instruments. Only relevant when check_visibility=True. Defaults to 10.0.
folder_path_override (str, optional) – If provided, the JSON file is saved directly to this path instead of the default data/measurements/radiometric or data/measurements/optical folder. The directory is created automatically if it does not exist. Defaults to None.

Return type:

None

property camera: Camera#: The camera object taking measurements.

property instrument: Instrument#: The instrument.

property name: str#: The name of the Centroiding model.

property sequence_definition: dict#: The sequence definition

property sigma: float#: The standard deviation of the measurements.

property state_definition: dict#: The state vector definition.

CentroidingIdeal#

`CentroidingIdeal`#