Cavok 0.1.1

Cavok

A METAR and TAF parser for .NET that treats the European ICAO format as a first-class citizen.

Metar metar = Metar.Parse("METAR EHAM 211125Z 24012G25KT 200V280 9999 -SHRA FEW012 BKN030CB 12/09 Q1013 TEMPO 4000 SHRA");

metar.Wind?.Direction         // 240
metar.Wind?.Gust?.Value       // 25
metar.Clouds[1].Type          // Cumulonimbus
metar.Pressure?.Hectopascals  // 1013
metar.FlightCategory          // Mvfr
metar.Describe(Language.Dutch)

METAR EHAM, waarneming dag 21 om 11:25 UTC
Wind:         240° met 12 kt, windstoten tot 25 kt, variërend tussen 200° en 280°
Zicht:        10 km of meer
Weer:         lichte regenbuien
Bewolking:    enkele wolken (1–2/8) op 1.200 ft, gebroken (5–7/8) op 3.000 ft met cumulonimbus
Temperatuur:  12 °C, dauwpunt 9 °C
QNH:          1013 hPa
Categorie:    MVFR
Trend:        tijdelijk: zicht 4.000 m; regenbuien

Why Cavok?

Most METAR libraries are written with US reports in mind. Cavok handles what European reports actually contain:

• CAVOK, QNH in hectopascals, NSC, NCD and NSW
• METAR trends — NOSIG, BECMG and TEMPO with FM, TL and AT
• TAF change groups — FM, BECMG, TEMPO, PROB30, PROB40 and PROB30 TEMPO, plus TX/TN
• Missing values from automatic stations (/////KT, ////, //////CB, 17///, RE//) without errors
• Runway visual range, runway state (including CLRD and SNOCLO), wind shear, sea state and military colour states (BLU+BLU+, BLACKBLU+, TEMPO WHT)

US and other reports parse as well: statute miles (1 1/2SM), A2992, CLR, RMK. US TAF low-level wind shear groups (WS020/24040KT) are not supported yet and are reported as errors.

Features

• Typed, immutable records for every group, with Parse (lenient) and ParseStrict (throws on errors)
• Precise diagnostics: every problem has a stable code (CAV004), the offending text and its position, and a caret view:

  error CAV004: invalid visibility group "2400O"; expected 4 digits (e.g. 0800, 9999)
    METAR EHAM 211125Z 24012KT 2400O -RA FEW012 12/09 Q1013
                               ^^^^^
  

• Never throws on bad input: one broken group does not stop the rest of the report from being parsed
• Flight category (VFR, MVFR, IFR, LIFR) for observations and every forecast block
• Plain-language descriptions in English and Dutch
• No dependencies; targets .NET Standard 2.0 and .NET 8

Install

dotnet add package Cavok

Usage

using Cavok;

Taf taf = Taf.Parse("TAF EHAM 210440Z 2106/2212 27005KT 9999 FEW035 BECMG 2106/2109 31011KT PROB30 TEMPO 2114/2118 TSRA");

foreach (TafChange change in taf.Changes)
{
    Console.WriteLine($"{change.Kind} {change.Probability} {change.Period}");
}

Console.WriteLine(taf.Describe(Language.English));

More examples are in the documentation.

How it is tested

• Unit tests for every group type, including the ICAO Annex 3 examples and edge cases
• Thousands of real METARs and TAFs from European aerodromes, fetched from the free aviationweather.gov Data API, must parse without errors
• A check that every group in the corpus is either understood or reported — nothing is dropped silently
• Snapshot tests of the parsed model and both descriptions for a diverse selection of reports
• Property-based fuzzing with FsCheck: random strings, random sequences of report groups and mutated real reports never make the parser throw

Development

dotnet test                                               # all tests
CAVOK_FUZZ_CASES=10000 dotnet test                        # more fuzzing
dotnet run --project tools/Cavok.Corpus -- fetch          # add fresh reports to the corpus
dotnet run --project tools/Cavok.Corpus -- triage         # see what the parser reports on the corpus
CAVOK_ACCEPT_SNAPSHOTS=1 dotnet test                      # accept intended snapshot changes

License

MIT