quaternionNorm function

double quaternionNorm(List<double> q)

The measured pose of the capture platform over the scene clock. Opcode 0x22.

Not the FourdgsCamera record, which is a viewing suggestion a reader may ignore. This is where the sensors were. The Euclidean norm of a quaternion, computed without squaring the components first.

A component near the top of the double range squares to infinity, so the naive sum reports an infinite norm for a rotation whose norm is finite and whose direction is perfectly good. Section 5.15.4 refuses "zero or non-finite norms" — a statement about the quaternion, not about the arithmetic used to measure it. Dividing by the largest magnitude first makes the sum safe.

Implementation

double quaternionNorm(List<double> q) {
  double scale = 0.0;
  for (final v in q) {
    final m = v.abs();
    if (m > scale) scale = m;
  }
  // Left for the caller to refuse, with the message it words for its own record.
  if (!scale.isFinite || scale == 0.0) return scale;
  double sum = 0.0;
  for (final v in q) {
    final u = v / scale;
    sum += u * u;
  }
  return scale * math.sqrt(sum);
}