pp_resampler — Wavelength-grid resampler

Group: Preprocessing · C ABI: n4m_transform_resampler_*

Description

Interpolate spectra from a fitted source wavelength grid to a target grid.

Parameters

Name	Type	Default
target_wavelengths	Sequence[float] | None	None
method	int	0
crop_min	float	0.0
crop_max	float	0.0
use_crop	bool	False
fill_value	float	0.0
bounds_error	bool	False
extrapolate	bool	False

API and bindings

C ABI (ABI 2): n4m_transform_resampler_create · n4m_transform_resampler_destroy · n4m_transform_resampler_fit · n4m_transform_resampler_is_fitted · n4m_transform_resampler_output_cols · n4m_transform_resampler_transform. Use the linked public header for the exact signature, configuration, and result handles.

Python (verified public re-export):

from n4m.transform.resampling import Resampler

Source signature: Resampler(target_wavelengths: Sequence[float] | None = None, method: int = 0, crop_min: float = 0.0, crop_max: float = 0.0, use_crop: bool = False, fill_value: float = 0.0, bounds_error: bool = False, extrapolate: bool = False, *, tgt_min: float | None = None, tgt_step: float | None = None, tgt_n: int | None = None).

R: no current source-verified entry point was found for this catalog method.

MATLAB / Octave: no current source-verified entry point was found for this catalog method.

Explanations

Bibliographic source

No single canonical paper: the supported linear, nearest, and not-a-knot cubic interpolants follow SciPy interpolation semantics documented at https://docs.scipy.org/doc/scipy/reference/generated/scipy.interpolate.CubicSpline.html.

Mathematical principle

Fit stores a strictly increasing source wavelength grid, optional crop indices, and target bracketing. Transform evaluates each row on configured target wavelengths by linear, nearest, or not-a-knot cubic interpolation, with explicit fill/extrapolation rules.

Appropriate uses

Harmonizing spectra acquired on different physical wavelength grids before transfer or modeling.

Limits and validation

Both grids must be ordered and represent the same physical coordinate. Extrapolation is poorly constrained; cubic interpolation can overshoot and resampling introduces correlated errors.

Implementation

n4m.transform.resampling.Resampler wraps n4m_transform_resampler_*; cached brackets and all three interpolation paths are in resampling/resampler.c.

The ABI-2 implementation is the n4m_transform_resampler_* lifecycle in libn4m.

Sources and provenance

https://docs.scipy.org/doc/scipy/reference/generated/scipy.interpolate.CubicSpline.html; https://github.com/GBeurier/nirs4all-methods/blob/main/cpp/src/core/preprocessing/resampling/resampler.c

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