Reflect terrain lab

The standalone explorer lives at /reflect/terrain/. No framework, external CDN, API key, or server-side simulation is required. Canvas 2D draws the isometric heightfield; a module Web Worker precomputes the day’s radiation with transferable typed arrays. The largest grid is 256 × 256. The solver retains one reusable frame, a four-value per-cell coefficient cache and a scalar energy timeline instead of storing all frames. At 256 × 256, returned simulation arrays occupy about 2 MiB (excluding inputs, the live frame and canvas). Rendering targets 60 fps, with controls updated at 20 Hz. Cached procedural paths add ripples, ice cracks and hummocks, forest canopies, grass tufts, rocks and snow drifts without image downloads. Dense grids are grouped according to available screen pixels for drawing; physics and tile inspection retain the full selected resolution. Canvas pixel count and device pixel ratio are capped. Reduced motion disables decorative light packets. Workers terminate after transferring their results.

Where to edit

• _pages/reflect-terrain.html: page copy, options, and the science explanation.
• assets/css/reflect.css: colours, typography, and responsive layout.
• assets/js/reflect/app.mjs: seeded world generation, surface presets and painting, inspector input ranges, canvas drawing, playback and CSV export.
• assets/js/reflect/model.mjs: the equation port, horizon shadows and energy integration. Constants match the supplied SpeedyWeather Julia implementation.
• assets/js/reflect/worker.mjs: background computation and transferable results.

The model consumes twelve values per cell in the order documented by FIELDS. The eleven learned land inputs include elevation, converted to geopotential with 9.80665 m/s², and snow depth, converted to percentage snow cover using the 0.05 m scale. The twelfth field is sea-ice concentration, used only over water. Vegetation fractions sum to at most 1. Temperatures are kelvin; soil moisture is m³/m³. Physical tile edits preserve other values, except vegetation adjustments which reduce the other cover when necessary. Painting replaces a tile’s surface properties with the brush preset; raising land applies a circular Gaussian brush with a 100 m peak, tapering to zero at a radius of max(2, grid width / 16) cells. Elevation is capped at 3000 m.

The 0–180° display is a solar arc, not zenith. Zenith is 90° → 0° → 90°. Midpoint integration uses 1440 intervals over the chosen daylight duration and is independent of animation timing. Cells are horizontal patches with terrain heights: shadows use east–west horizons, direct sunlight is blocked in shadow, and diffuse sunlight is not. This is not a latitude/date astronomical model, a full atmospheric radiation model, or a terrain-slope/vegetation shadow model. The original broadband weights (which sum to 1.0084) are preserved, followed by the original final clamp. No renormalisation is applied.

Vertical gauges show instantaneous incident and reflected irradiance in W/m². Accumulated energy is interpolated from the integrated timeline. kWh/m² is the area mean across every cell. Each cell is 10,000 m²; the MWh figure is the landscape total. CSV exports contain 1441 cumulative timeline points. Edits invalidate results and reset energy. Playback speed (0.5× to 8×) changes only animation duration, never the integration interval or final energy.

Desktop layout fits the viewport, with compact controls and dialogs for science and tile inputs. Small screens use normal vertical scrolling for readability.

Validation and preview

node scripts/test_reflect.mjs
bundle exec jekyll build
bundle exec jekyll serve

Open http://127.0.0.1:4000/reflect/terrain/. ES modules and Web Workers require HTTP; opening the HTML directly with file:// will not run the application.

Numerical checks cover analytical flat-day irradiation, energy conservation, snow/ice endpoints, daylight scaling, terrain shadows, diffuse-only invariance, and Julia-derived C45 fixtures. Three reference BRDF cases were independently evaluated using Julia 1.12 and matched the JavaScript implementation to machine precision. Local Chrome checks covered worker startup, scrubbing, tile editing, preset generation, positive daily totals, and a 390 px mobile viewport.