The search binary searches the sample list to interpolate between the two
samples that straddle a crossing, and a binary search over an unordered
list returns a wrong index instead of failing. Only the first and last
times were checked, so a sequence whose ends were in order but whose
middle was not refined each crossing against the wrong pair of positions
and reported a pass that never happened. On a circular ground track,
shuffling two samples changed the result from three passes to two and
still returned Ok.
The whole sequence is now checked, with a new UnorderedSamples error kind
that says which pair is out of order. The test covers the middle-of-
sequence case that the end check missed.
Two comments also described something other than what the code does, and
two Option-returning accessors did not say what makes them None:
- GravityModel::x2o3 is the constant 2/3, used as an exponent in the
mean motion and drag corrections, not 2 * xke^2 as its comment claimed;
the sgp4 reference implementation uses the same constant the same way.
- WalkerPattern::plane_spacing and phase_offset returned None without
saying so, which is the case a caller has to handle.
Both READMEs claimed twelve expect sites where there are thirteen, because
apsis-math/src/parallel.rs added one and the count was not carried over.
The choice of which loops to thread follows the cost of one item and the
size of the batch, and the note records both ends: the propagation that
gains five fold over a month and barely gains over a day, and the
visibility sweep that is slower in parallel below a few hundred satellites
because a single test costs a few nanoseconds. The interfaces say the same
thing, so a caller knows when to reach for them.
A coverage run wants a satellite's state at every minute of a day, and each
state is independent, so the loop is a candidate for several cores and the
work is large enough to pay for the threads. The parallel form returns the
same values in the same order as the sequential one, including reporting a
decayed instant as None rather than stopping early.
ApsisRS contributors