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//! Shared RINEX header concepts used across the RINEX family of readers.
//!
//! The observation, navigation, and clock readers all decode the same RINEX
//! header time-system field. Keeping the label mapping here (rather than
//! duplicating it per reader, or borrowing it from an unrelated parser module)
//! gives the family one canonical, format-faithful decode and serialize point.
use std::collections::BTreeMap;
use crate::astro::time::civil::j2000_seconds;
use crate::astro::time::model::TimeScale;
use crate::rinex_obs::ObsEpochTime;
/// Map a RINEX header time-system label onto the core [`TimeScale`].
///
/// Returns `None` for an empty or unrecognized label so each reader can apply
/// its own policy for the unknown case (the observation/clock readers default a
/// blank label to GPST, an explicit unknown label is rejected). The RINEX/SP3
/// `GLO` time system is defined as UTC (RINEX 3 spec), not the UTC+3h GLONASS
/// system time: [`TimeScale::Glonasst`] is a conversion-only variant and is
/// never produced by parsing a file's time-system label.
pub(crate) fn time_scale_label(label: &str) -> Option<TimeScale> {
match label.trim() {
"GPS" => Some(TimeScale::Gpst),
"QZS" => Some(TimeScale::Qzsst),
"GLO" => Some(TimeScale::Utc),
"GAL" => Some(TimeScale::Gst),
"BDT" => Some(TimeScale::Bdt),
"UTC" => Some(TimeScale::Utc),
"TAI" => Some(TimeScale::Tai),
_ => None,
}
}
/// The canonical RINEX header time-system label for a core [`TimeScale`].
///
/// The inverse of [`time_scale_label`] for the scales a RINEX header can name,
/// used by the serializers so a parsed product round-trips its time system.
/// `GLO` is intentionally not emitted: a `GLO` label decodes to [`TimeScale::Utc`]
/// (the two are indistinguishable after parsing), so `Utc` serializes as `UTC`.
pub(crate) fn time_scale_rinex_label(scale: TimeScale) -> &'static str {
match scale {
TimeScale::Gpst => "GPS",
TimeScale::Qzsst => "QZS",
TimeScale::Gst => "GAL",
TimeScale::Bdt => "BDT",
TimeScale::Utc => "UTC",
TimeScale::Tai => "TAI",
// No RINEX header label maps to these scales; GPST is the RINEX default
// time system and keeps a serialized header parseable.
TimeScale::Tt | TimeScale::Tdb | TimeScale::Glonasst => "GPS",
}
}
pub(crate) fn obs_epoch_seconds(epoch: ObsEpochTime) -> f64 {
j2000_seconds(
epoch.year,
i32::from(epoch.month),
i32::from(epoch.day),
i32::from(epoch.hour),
i32::from(epoch.minute),
epoch.second,
)
}
pub(crate) fn dominant_obs_interval_s(times: &[ObsEpochTime]) -> Option<f64> {
let mut counts: BTreeMap<i64, usize> = BTreeMap::new();
for pair in times.windows(2) {
let delta_ms =
((obs_epoch_seconds(pair[1]) - obs_epoch_seconds(pair[0])) * 1000.0).round() as i64;
if delta_ms > 0 {
*counts.entry(delta_ms).or_default() += 1;
}
}
counts
.into_iter()
.max_by_key(|(delta_ms, count)| (*count, -(*delta_ms)))
.map(|(delta_ms, _)| delta_ms as f64 / 1000.0)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn known_labels_round_trip() {
for label in ["GPS", "QZS", "GAL", "BDT", "UTC", "TAI"] {
let scale = time_scale_label(label).expect("known label");
assert_eq!(time_scale_rinex_label(scale), label);
}
}
#[test]
fn glonass_label_is_utc() {
assert_eq!(time_scale_label("GLO"), Some(TimeScale::Utc));
// UTC serializes back as UTC (GLO and UTC are indistinguishable).
assert_eq!(time_scale_rinex_label(TimeScale::Utc), "UTC");
}
#[test]
fn unknown_label_is_none() {
assert_eq!(time_scale_label("XYZ"), None);
assert_eq!(time_scale_label(""), None);
}
}