snow_rendering

Turn weather data into driving safety guidance. snow_rendering classifies road surface conditions, computes grip factors, and derives visibility and precipitation parameters from real weather observations.

Pure Dart — no Flutter dependency. Safe to use from any Dart environment.

0.3.0 fixes a safety defect present through 0.2.7. A road whose conditions could not be classified fell through to RoadSurfaceState.dry, gripFactor: 1.0, RecommendedResponse.proceed and the advisory "Conditions normal" — a confident green light over a road nobody had measured. surfaceState and gripFactor are now nullable and a conditionsUnknown response tier exists. Read the CHANGELOG before upgrading — the compile errors are the fix.

Features

• RoadSurfaceState — six-state classification (dry, wet, slush, compactedSnow, blackIce, standingWater) with grip factors, including the humidity-gated radiative-frost black-ice window (clear sky, ambient a few degrees above 0 °C, road surface frozen)
• RoadSurfaceState.announcement — driver-facing spoken lines (JA + EN) leading with the precise JP-domestic surface term (ブラックアイスバーン / 圧雪 / シャーベット), possibility-graded; plus invisibleBlackIceAnnouncement carrying the "looks merely wet" fact and the verbatim JAF advisory for invisible-ice paths
• DrivingConditionAssessment — combined assessment with advisory message from a single WeatherCondition
• PrecipitationConfig — particle count, velocity, size, and lifetime parameters by type and intensity
• VisibilityDegradation — opacity and blur sigma from visibility distance in metres
• HysteresisFilter<T> — debounce filter preventing rapid oscillation at boundary conditions

Install

dependencies:
  snow_rendering: ^0.3.0

Quick Start

import 'package:driving_weather/driving_weather.dart';
import 'package:snow_rendering/snow_rendering.dart';

final condition = WeatherCondition(
  precipType: PrecipitationType.snow,
  intensity: PrecipitationIntensity.heavy,
  temperatureCelsius: -5,
  visibilityMeters: 400,
  windSpeedKmh: 30,
  iceRisk: false,
  timestamp: DateTime.now(),
);

final assessment = DrivingConditionAssessment.fromCondition(condition);

// NULLABLE (0.3.0): a road the classifier could not assess has NO surface and
// NO grip coefficient. `null` does not mean `dry`, and it does not mean 1.0 —
// inventing either is the defect this release removes.
print(assessment.surfaceState);    // RoadSurfaceState.compactedSnow (or null)
print(assessment.gripFactor);      // 0.3 (or null — surface not classified)
print(assessment.advisoryMessage); // Compacted snow — use winter tyres, reduce speed
print(assessment.visibility?.blurSigma);        // 2.0 (or null — not measured)
print(assessment.precipitation?.particleCount); // 500 (or null — not measured)

// The tier tells you which case you are in — exhaustively.
switch (assessment.recommendedResponse) {
  case RecommendedResponse.proceed:            // assessed, and benign
  case RecommendedResponse.reduceSpeed:        // hazard
  case RecommendedResponse.considerTurningBack:// whiteout class
  case RecommendedResponse.conditionsUnknown:  // NOT assessed — say so
    print(RecommendedResponse.conditionsUnknown.announcement!.jaSpokenText);
    // 路面状況を取得できていません。見える範囲で運転してください。
}

Debounced Classification

Wrap in HysteresisFilter to prevent flickering at boundary conditions:

// NOTE the nullable type argument: `fromCondition` returns `RoadSurfaceState?`
// in 0.3.0 — a road it cannot classify has no surface, and must not be
// debounced into `dry`.
final filter = HysteresisFilter<RoadSurfaceState?>();
// Requires the same state in 2 of last 3 readings before transitioning.
final stable = filter.update(RoadSurfaceState.fromCondition(condition));

Road Surface States