pp_xcorr_align — Whole-spectrum cross-correlation alignment¶
Group: Signal transforms · C ABI: n4m_transform_xcorr_align_*
Description¶
Whole-spectrum integer shift chosen by maximum correlation.
Parameters¶
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API and bindings¶
C ABI (ABI 2): n4m_transform_xcorr_align_create · n4m_transform_xcorr_align_destroy · n4m_transform_xcorr_align_fit · n4m_transform_xcorr_align_is_fitted · n4m_transform_xcorr_align_transform. Use the linked public header for the exact signature, configuration, and result handles.
Python (verified public re-export):
from n4m.transform.alignment import CrossCorrelationAlignment
Source signature: CrossCorrelationAlignment(reference = None, max_shift: int = 5).
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 defines this bounded implementation. It applies the standard discrete cross-correlation lag estimator; the source defines padding and tie behaviour.
Mathematical principle¶
For each row, every integer lag in [-max_shift,max_shift] is evaluated by the centered dot product with the fitted reference. The best lag is applied to the whole spectrum using edge-replicated samples.
Appropriate uses¶
Correcting one global channel offset per spectrum before comparison or calibration.
Limits and validation¶
It cannot model local stretching, and amplitude/shape changes can move the correlation maximum. Edge replication affects shifted ends; weak or periodic spectra can have ambiguous lags.
Implementation¶
n4m.transform.alignment.CrossCorrelationAlignment wraps n4m_transform_xcorr_align_*; reference fitting and lag search are in cpp/src/c_api/c_api_advanced.cpp.
The ABI-2 implementation is the n4m_transform_xcorr_align_* lifecycle in libn4m.
Sources and provenance¶
https://github.com/GBeurier/nirs4all-methods/blob/main/cpp/src/c_api/c_api_advanced.cpp#L798-L900
See also: methods index · interactive dashboard