Function lupnt::safe_acos

Function Documentation

Real lupnt::safe_acos(Real x)

Compute the safe acos function.

Numerically robust acos, clamping the input to [-1, 1] (offset by EPS) before evaluating, to avoid NaNs from values that are out of range only due to floating-point round-off.

Used throughout geometry/elevation-angle computations — e.g. GnssMeasurement’s elevation/off-boresight angles, GnssAttitude’s yaw/attitude angles, and orbital-element conversions (inclination from angular-momentum components) — wherever the acos argument is a dot product of unit vectors that may slightly exceed +/-1 due to round-off.

Parameters:

  • x – Input value

  • x – Cosine value, nominally in [-1, 1]

Returns:

acos(x) if x is in [-1, 1], otherwise acos(x - EPS) or acos(x + EPS)

Returns:

acos(x), with x clamped to (-1, 1) if it lies (slightly) outside