ztforce.utils

Pure math helpers — no ztforce imports.

Functions

flux_to_ab_mag(→ tuple[float, float | None])	Convert instrumental flux to AB magnitude.
ab_mag_to_flux(→ tuple[float, float | None])	Convert AB magnitude to instrumental flux.
snr_from_flux(→ float)	Signal-to-noise ratio from flux and its uncertainty.
has_nan_nearby(→ bool)	Return True if any pixel within radius of (row, col) is masked.
nearest_odd_int(→ int)	Round x up to the nearest odd integer.
annular_background(→ tuple[float, float])	Sigma-clipped sky level and RMS in an annulus around (cx, cy).

Module Contents

flux_to_ab_mag(flux: float, zero_point: float, flux_err: float | None = None) → tuple[float, float | None]

Convert instrumental flux to AB magnitude.

Uses the AB system definition from Oke & Gunn (1983, ApJ, 266, 713): mag = zero_point - 2.5 * log10(flux).

Returns (mag, mag_err). mag_err is None when flux_err is not given. Returns (nan, nan) when flux <= 0.

ab_mag_to_flux(mag: float, zero_point: float, mag_err: float | None = None) → tuple[float, float | None]

Convert AB magnitude to instrumental flux.

Returns (flux, flux_err). flux_err is None when mag_err is not given.

snr_from_flux(flux: float, flux_err: float) → float

Signal-to-noise ratio from flux and its uncertainty.

has_nan_nearby(row: int, col: int, radius: float, mask: numpy.ndarray) → bool

Return True if any pixel within radius of (row, col) is masked.

nearest_odd_int(x: float) → int

Round x up to the nearest odd integer.

annular_background(data: numpy.ndarray, cx: float, cy: float, r_inner: float, r_outer: float, sigma: float = 3.0) → tuple[float, float]

Sigma-clipped sky level and RMS in an annulus around (cx, cy).

cx/cy follow the FITS/numpy column/row convention (cx = column index). Returns (sky_level, sky_rms). Falls back to the global finite-pixel statistics when fewer than 5 annulus pixels are available.