feat: 新增月掩与日月食地理绘图并提升观测计算精度
- 新增月掩恒星和行星：支持搜索、掩甚点、全球掩带及固定地点轨迹计算 - 支持恒星星表坐标转换、有限盘面行星接触事件和月掩 SVG 输出 - 新增日月食及月掩全球投影图、时间标记和 GeoJSON 地理数据接口 - 扩展日食中心线、南北界及偏食足迹采样，支持极区投影 - 修正站心时角、月出月落、月球视半径、折射和恒星自行计算 - 优化内外行星事件搜索、边界选择、极端输入处理和计算稳定性
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package basic
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import (
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"math"
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"time"
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)
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const (
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planetOccultationFootprintBoundaryPoints = 180
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planetOccultationHorizonPoints = 360
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planetOccultationFootprintMaxSamples = 360
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)
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type planetOccultationFootprintSample struct {
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point OccultationPathPoint
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ok bool
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}
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func planetOccultationFootprints(
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startTT, endTT, greatestTT float64,
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frameAt occultationPathFrameFunc,
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options OccultationPathOptions,
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location *time.Location,
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) []PlanetOccultationFootprint {
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stepDays := float64(options.Step) / float64(24*time.Hour)
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times := occultationPathSampleTimesWithLimit(
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startTT, endTT, greatestTT, stepDays, planetOccultationFootprintMaxSamples,
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)
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footprints := make([]PlanetOccultationFootprint, 0, len(times))
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for _, tt := range times {
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footprint, ok := planetOccultationFootprintAt(tt, frameAt, location)
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if ok {
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footprints = append(footprints, footprint)
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}
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}
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return footprints
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}
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func planetOccultationFootprintAt(
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tt float64,
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frameAt occultationPathFrameFunc,
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location *time.Location,
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) (PlanetOccultationFootprint, bool) {
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frame, ok := frameAt(tt)
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if !ok {
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return PlanetOccultationFootprint{}, false
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}
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samples := make([]planetOccultationFootprintSample, planetOccultationFootprintBoundaryPoints)
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for index := range samples {
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theta := 2 * math.Pi * float64(index) / float64(len(samples))
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vector, _, valid := occultationPathBoundaryVector(frame, theta)
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if valid {
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samples[index] = planetOccultationFootprintSample{
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point: occultationPathPointFromVector(tt, vector, 0, location),
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ok: true,
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}
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}
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}
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segments, closed := planetOccultationFootprintSegments(samples)
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polygons := make([][]OccultationPathPoint, 0, len(segments))
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for _, segment := range segments {
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if len(segment) < 2 {
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continue
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}
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polygon := append([]OccultationPathPoint(nil), segment...)
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if closed {
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polygon = append(polygon, polygon[0])
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} else {
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polygon = append(polygon, planetOccultationHorizonArc(tt, frame, segment[len(segment)-1], segment[0], location)...)
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}
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if len(polygon) >= 4 {
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polygons = append(polygons, polygon)
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}
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}
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if len(polygons) == 0 {
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return PlanetOccultationFootprint{}, false
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}
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return PlanetOccultationFootprint{
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Time: occultationTTToLocation(tt, location),
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Polygons: polygons,
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}, true
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}
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func planetOccultationFootprintSegments(
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samples []planetOccultationFootprintSample,
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) ([][]OccultationPathPoint, bool) {
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segments := make([][]OccultationPathPoint, 0, 2)
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current := make([]OccultationPathPoint, 0, len(samples))
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allValid := len(samples) > 0
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for _, sample := range samples {
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if !sample.ok {
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allValid = false
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if len(current) > 0 {
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segments = append(segments, current)
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current = nil
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}
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continue
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}
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current = append(current, sample.point)
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}
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if len(current) > 0 {
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segments = append(segments, current)
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}
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if len(segments) > 1 && samples[0].ok && samples[len(samples)-1].ok {
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first := segments[0]
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last := segments[len(segments)-1]
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merged := make([]OccultationPathPoint, 0, len(last)+len(first))
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merged = append(merged, last...)
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merged = append(merged, first...)
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segments[0] = merged
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segments = segments[:len(segments)-1]
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}
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return segments, allValid && len(segments) == 1
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}
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func planetOccultationHorizonArc(
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tt float64,
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frame occultationPathFrame,
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from, to OccultationPathPoint,
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location *time.Location,
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) []OccultationPathPoint {
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sublunarLongitude, sublunarLatitude := occultationPathGeodetic(tt, frame.moon)
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circle := planetOccultationSphericalCircle(
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occultationTTToLocation(tt, location), sublunarLongitude, sublunarLatitude,
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90, planetOccultationHorizonPoints,
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)
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fromIndex := planetOccultationNearestPointIndex(circle, from)
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toIndex := planetOccultationNearestPointIndex(circle, to)
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forwardSteps := (toIndex - fromIndex + len(circle)) % len(circle)
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backwardSteps := (fromIndex - toIndex + len(circle)) % len(circle)
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direction := 1
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steps := forwardSteps
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if backwardSteps < forwardSteps {
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direction = -1
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steps = backwardSteps
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}
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arc := make([]OccultationPathPoint, 0, steps+1)
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for step := 1; step < steps; step++ {
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index := (fromIndex + direction*step) % len(circle)
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if index < 0 {
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index += len(circle)
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}
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arc = append(arc, circle[index])
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}
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return append(arc, to)
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}
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func planetOccultationSphericalCircle(
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value time.Time,
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centerLongitude, centerLatitude, radius float64,
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count int,
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) []OccultationPathPoint {
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centerLongitude *= math.Pi / 180
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centerLatitude *= math.Pi / 180
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radius *= math.Pi / 180
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points := make([]OccultationPathPoint, count)
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for index := range points {
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bearing := 2 * math.Pi * float64(index) / float64(count)
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latitude := math.Asin(
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math.Sin(centerLatitude)*math.Cos(radius) +
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math.Cos(centerLatitude)*math.Sin(radius)*math.Cos(bearing),
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)
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longitude := centerLongitude + math.Atan2(
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math.Sin(bearing)*math.Sin(radius)*math.Cos(centerLatitude),
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math.Cos(radius)-math.Sin(centerLatitude)*math.Sin(latitude),
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)
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points[index] = OccultationPathPoint{
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Time: value,
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Longitude: normalizeLongitude(longitude * 180 / math.Pi),
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Latitude: latitude * 180 / math.Pi,
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}
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}
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return points
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}
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func planetOccultationNearestPointIndex(points []OccultationPathPoint, target OccultationPathPoint) int {
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nearest := 0
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distance := math.Inf(1)
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for index, point := range points {
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candidate := occultationPathDistanceKM(point, target)
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if candidate < distance {
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nearest = index
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distance = candidate
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}
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}
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return nearest
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}
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