sga

HydroErr.HydroErr.sga(simulated_array: ndarray[tuple[Any, ...], dtype[floating | integer]] | Sequence[int | float], observed_array: ndarray[tuple[Any, ...], dtype[floating | integer]] | Sequence[int | float], replace_nan: float | None = None, replace_inf: float | None = None, remove_neg: bool = False, remove_zero: bool = False) → floating[Any]

Compute the Spectral Gradient Angle (SGA).

\[SG_o = (O_2-O_1, O_3-O_2,...,O_n-O_{n-1})\]
\[SG_s = (S_2-S_1, S_3-S_2,...,S_n-S_{n-1})\]
\[SGA = SA(SG_o, SG_s)\]
\[\text{Note: SA=Spectral Angle Metric}\]

Range: -π/2 ≤ SID < π/2, closer to 0 is better.

Notes: The spectral gradient angle measures the angle between the two vectors in hyperspace. It indicates how well the shape of the two series match - not magnitude. SG is the gradient of the simulated or observed time series.

Parameters:

  • simulated_array – An array of simulated data from the time series.

  • observed_array – An array of observed data from the time series.

  • replace_nan – If given, indicates which value to replace NaN values with in the two arrays. If None, when a NaN value is found at the i-th position in the observed OR simulated array, the i-th value of the observed and simulated array are removed before the computation.

  • replace_inf – If given, indicates which value to replace Inf values with in the two arrays. If None, when an inf value is found at the i-th position in the observed OR simulated array, the i-th value of the observed and simulated array are removed before the computation.

  • remove_neg – If True, when a negative value is found at the i-th position in the observed OR simulated array, the i-th value of the observed AND simulated array are removed before the computation.

  • remove_zero – If true, when a zero value is found at the i-th position in the observed OR simulated array, the i-th value of the observed AND simulated array are removed before the computation.

Return type:

The Spectral Gradient Angle.

Examples

>>> import HydroErr as he
>>> import numpy as np

>>> sim = np.array([5, 7, 9, 2, 4.5, 6.7])
>>> obs = np.array([4.7, 6, 10, 2.5, 4, 7])
>>> he.sga(sim, obs)
0.26764286472739834

References

  • Robila, S.A., Gershman, A., 2005. Spectral matching accuracy in processing hyperspectral data, Signals, Circuits and Systems, 2005. ISSCS 2005. International Symposium on. IEEE, pp. 163-166.