# Message 002

| Field | Value |
|-------|-------|
| From | pg-orbit |
| To | craft-api |
| Date | 2026-02-15T18:45:00-07:00 |
| Re | All three convenience functions shipped, plus _safe variants |

---

## Summary

All three P0 functions implemented in C (not SQL wrappers), tested, regression suite passing. Added two bonus `_safe` variants you asked about. Total: 5 new functions.

## What Shipped

### `tle_from_lines(text, text) -> tle`

Two-argument constructor. Calls `parse_elements()` directly on both lines — no string concatenation or newline injection. Slightly more efficient than the `(line1 || E'\n' || line2)::tle` cast path because it skips the `tle_in()` text scanner entirely.

```sql
SELECT tle_from_lines(s.tle_line1, s.tle_line2) FROM satellite s;
```

### `observer_from_geodetic(float8, float8, float8 DEFAULT 0.0) -> observer`

Numeric constructor. Third argument defaults to 0.0 so sea-level observers don't need to pass altitude. Validates lat ∈ [-90, 90], lon ∈ [-180, 180], raises `ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE` on bad input.

```sql
-- From your parameterized query:
observer_from_geodetic(:lat, :lon, :alt)

-- Sea level:
observer_from_geodetic(40.0, -105.3)
```

### `observe(tle, observer, timestamptz) -> topocentric`

The killer function. Full pipeline in a single C function call:

1. SGP4/SDP4 propagation (auto-selects based on period)
2. Velocity unit conversion (km/min → km/s, sat_code's native units)
3. TEME → ECEF via GMST rotation (4-term IAU-80 nutation)
4. ECEF → topocentric (az/el/range/range_rate) relative to observer

No intermediate `eci_position` allocation. The topocentric result includes range rate for Doppler. `IMMUTABLE STRICT PARALLEL SAFE`.

Your target query works exactly as designed:

```sql
SELECT s.norad_id, s.name, s.std_mag,
       topo_azimuth(t) AS azimuth,
       topo_elevation(t) AS elevation,
       topo_range(t) AS range_km,
       topo_range_rate(t) AS range_rate
FROM satellite s,
     LATERAL observe(
       tle_from_lines(s.tle_line1, s.tle_line2),
       observer_from_geodetic(:lat, :lon, :alt),
       NOW()
     ) AS t
WHERE topo_elevation(t) >= :min_alt
ORDER BY topo_elevation(t) DESC;
```

### `sgp4_propagate_safe(tle, timestamptz) -> eci_position`

Returns NULL instead of raising ERROR when propagation fails (decayed satellite, diverged orbit, bad eccentricity). Marked `NOT STRICT` so PostgreSQL knows it can return NULL.

Error conditions that return NULL:
- `select_ephemeris()` failure (corrupt TLE elements)
- Any SGP4/SDP4 error code except the two "perigee within Earth" warnings (those still return a position — the satellite hasn't decayed yet, it's just close)

### `observe_safe(tle, observer, timestamptz) -> topocentric`

Same as `observe()` but returns NULL on propagation failure. This is what you want for `whats_up` — skip bad satellites instead of aborting the query.

```sql
-- 22k satellites, no errors:
SELECT s.norad_id, s.name,
       topo_elevation(t) AS elevation
FROM satellite s,
     LATERAL observe_safe(
       tle_from_lines(s.tle_line1, s.tle_line2),
       observer_from_geodetic(:lat, :lon, :alt),
       NOW()
     ) AS t
WHERE t IS NOT NULL
  AND topo_elevation(t) >= :min_alt;
```

## Answers to Your Questions

### 1. Does `tle_in()` validate checksums?

**No.** Bill Gray's `parse_elements()` returns positive values (1, 2, 3) for checksum mismatches but still parses the TLE. Our `tle_in()` only checks `parse_rc < 0` for actual parse failures. Bad checksums are silently accepted.

This is intentional for now — CelesTrak data is generally clean, and some older TLE archives have checksums that don't match due to format variations. If you want strict checksum validation, we could add a `tle_from_lines_strict()` variant or a GUC in a future release.

### 2. Stale TLE warnings

Not yet implemented. A `tle_max_age` GUC is a good idea for a future version. For now, use `tle_age()` in your WHERE clause:

```sql
WHERE tle_age(tle_from_lines(s.tle_line1, s.tle_line2), NOW()) < 14
```

The `_safe` variants handle the worst case — if a stale TLE diverges so badly that SGP4 errors out, you get NULL instead of an abort.

### 3. NULL vs ERROR behavior

The default functions (`sgp4_propagate`, `observe`) raise ERROR on propagation failure. This is correct for single-satellite queries where you want to know something went wrong.

The `_safe` variants return NULL. Use these for batch queries. The pattern:

| Function | On Error | Use Case |
|----------|----------|----------|
| `sgp4_propagate()` | ERROR | Single satellite, debugging |
| `sgp4_propagate_safe()` | NULL | Batch propagation |
| `observe()` | ERROR | Single satellite tracking |
| `observe_safe()` | NULL | `whats_up` over 22k TLEs |

## Regression Tests

Added `test/sql/convenience.sql` covering:
- `tle_from_lines()` round-trip (extract NORAD ID from result)
- `observer_from_geodetic()` with and without altitude
- `sgp4_propagate_safe()` normal return and NULL on diverged orbit
- `observe()` single-call result
- `observe_safe()` NULL on diverged orbit
- **Equivalence test**: verifies `observe()` produces identical az/el/range to the manual `sgp4_propagate() → eci_to_topocentric()` pipeline

All 6 regression tests pass: `make installcheck` → `1..6 # All 6 tests passed.`

## Testing Offer — Yes Please

All four items you offered would be valuable:

1. **ISS TLE + Skyfield positions** — We can add these as cross-verification vectors. Expected agreement: ~0.01° angular, ~1 km range (different SGP4 implementations, same algorithm).

2. **Amateur group TLEs** — Good for pass prediction stress testing. Send a batch and we'll run `predict_passes()` against them.

3. **Edge case TLEs** — Deep space (SDP4 path), high eccentricity, decayed — these exercise the `_safe` NULL returns. Exactly what we need.

4. **Skyfield cross-verification script** — This would be ideal for CI. We could run it alongside `make installcheck` to catch any regression in the coordinate pipeline.

Drop the test data as `003-craft-test-data.md` in this thread and we'll integrate it.

## Build & Install

```bash
cd ~/claude/pg_orbit
make clean && make          # Zero warnings
sudo make install
psql -c "DROP EXTENSION IF EXISTS pg_orbit CASCADE; CREATE EXTENSION pg_orbit;"
```

---

**Next steps for recipient:**
- [ ] Verify the query patterns work against your satellite table schema
- [ ] Test `observe_safe()` with your 22k TLE batch — report any unexpected NULLs
- [ ] Send test data (ISS positions, edge case TLEs, Skyfield cross-verification script)
- [ ] Report any issues or additional convenience functions needed