See how visible the eclipse is from where you are!
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export type CoverageCell = { longitude: number latitude: number coverage: number size: number}
export type CoverageSurface = { centre: { longitude: number; latitude: number } cells: CoverageCell[]}
const HOUR = 60 * 60 * 1_000
function maximumCoverage(longitude: number, latitude: number, peak: Date): number { const start = peak.getTime() - 4 * HOUR const end = peak.getTime() + 4 * HOUR let bestTime = start let maximum = 0
for (let time = start; time <= end; time += 15 * 60_000) { const geometry = solarDiscGeometry({ latitude, longitude }, new Date(time)) if (geometry.sunAltitude > 0 && geometry.coverage > maximum) { maximum = geometry.coverage bestTime = time } }
for (let time = bestTime - 15 * 60_000; time <= bestTime + 15 * 60_000; time += 60_000) { const geometry = solarDiscGeometry({ latitude, longitude }, new Date(time)) if (geometry.sunAltitude > 0) maximum = Math.max(maximum, geometry.coverage) } return maximum}
function pointKey(longitude: number, latitude: number): string { return `${longitude.toFixed(2)},${latitude.toFixed(2)}`}
function addNeighbourhood(target: Map<string, [number, number]>, longitude: number, latitude: number, radius: number, step: number) { for (let candidateLatitude = latitude - radius; candidateLatitude <= latitude + radius; candidateLatitude += step) { if (candidateLatitude < -89 || candidateLatitude > 89) continue for (let candidateLongitude = longitude - radius; candidateLongitude <= longitude + radius; candidateLongitude += step) { const wrappedLongitude = ((candidateLongitude + 540) % 360) - 180 target.set(pointKey(wrappedLongitude, candidateLatitude), [wrappedLongitude, candidateLatitude]) } }}
export function generateCoverageSurface( peak: Date, suggestedCentre: { longitude?: number; latitude?: number } = {},): CoverageSurface { const fineCandidates = new Map<string, [number, number]>() for (let latitude = -88; latitude <= 88; latitude += 4) { for (let longitude = -180; longitude < 180; longitude += 4) { if (maximumCoverage(longitude, latitude, peak) >= .002) { addNeighbourhood(fineCandidates, longitude, latitude, 4, 2) } } }
const fineCells: CoverageCell[] = [] const hotspotCandidates = new Map<string, [number, number]>() let best = { longitude: suggestedCentre.longitude ?? -12, latitude: suggestedCentre.latitude ?? 48, coverage: 0, }
for (const [longitude, latitude] of fineCandidates.values()) { const coverage = maximumCoverage(longitude, latitude, peak) if (coverage < .005) continue fineCells.push({ longitude, latitude, coverage, size: 2.08 }) if (coverage > best.coverage) best = { longitude, latitude, coverage } if (coverage >= .55) addNeighbourhood(hotspotCandidates, longitude, latitude, 2, 1) }
const hotspotCells: CoverageCell[] = [] for (const [longitude, latitude] of hotspotCandidates.values()) { const coverage = maximumCoverage(longitude, latitude, peak) if (coverage < .5) continue hotspotCells.push({ longitude, latitude, coverage, size: 1.06 }) if (coverage > best.coverage) best = { longitude, latitude, coverage } }
return { centre: { longitude: best.longitude, latitude: best.latitude }, cells: [...fineCells, ...hotspotCells], }}