See the light before you go.
Move through time. Place an observer. Watch the terrain meet the sun.
Reference reconstruction / Spacetime integration
What the reference actually does
Fuji Sun by Alastair Tse predicts when the solar disc overlaps the summit of Mount Fuji from a selected viewpoint. The shared post demonstrates 2 November at 16:33 JST from Tokyo Tower.
- Read the observer’s ground elevation and add eye height.
- Compute distance, bearing and apparent summit elevation, including Earth curvature and a terrestrial refraction coefficient of 0.13.
- Compute the Sun’s apparent azimuth and elevation with NOAA / Meeus equations and atmospheric refraction.
- Search each day for an azimuth match; compare the residual elevation to the Sun’s angular radius.
- Sample terrain and buildings along sightlines to test occlusion; render map and observer view from the same state.
Inspection of the public deployed application identifies SvelteKit, MapLibre GL JS and Three.js, a terrain height-field renderer, sky scattering and terrain-tile adapters. No public application repository or license was located. The original offers multiple elevation sources, focal lengths, buildings and location search. It states that trees are absent and the weather control changes the picture only.
Original implementation in this reconstruction
This file implements the geometry independently. It does not reproduce the creator’s code, imagery or interface. The Ojai scene uses a deterministic synthetic valley and a sampled horizon. The Fuji mode isolates the documented Tokyo-to-summit geometry and analytic summit silhouette; intervening terrain is unknown.
NOAA calculation details describe the astronomical and refraction approximations. Atmospheric conditions can change observed alignment times; this prototype does not attach a certified error bound.
What carries into Spacetime
| Mechanism | Product use |
|---|---|
| Shared time state | Scrub a place and time across globe, FPV, probe and machine query. |
| Observer horizon | Terrain-limited optical visibility and sunlight availability. |
| Event solver | Search bounded intervals for visibility transitions, then refine brackets. |
| Evidence record | Return source, datum, resolution, sampling and missing coverage with the result. |
| Offline package | Cache a bounded area, source manifest and deterministic computation for edge operation. |
Production critical path
- Replace the analytic terrain adapter with a versioned DEM tile package. Resolve vertical datums before mixing terrain, eye heights or buildings.
- Add bounded ray intersection against terrain and surface/building geometry. Return unknown when required coverage is missing.
- Validate against surveyed horizons and timestamped observations at representative ranges and elevations.
- Expose the same state through
get_environment,explain_stateand a visibility event query.
Terrain attribution depends on the chosen package: the source cites Tilezen / AWS, Mapterhorn / Re:Earth, GSI Japan, and Overture / OpenStreetMap buildings. Verify the dataset’s current license and preserve required attribution before redistribution.