248 lines
10 KiB
Go
248 lines
10 KiB
Go
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package basic
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import (
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"math"
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"sort"
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)
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const (
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starOccultationDiagramDefaultStepDays = 2.0 / 1440.0
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starOccultationDiagramMinStepDays = 1.0 / 86400.0
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starOccultationDiagramMaxSamples = 2000
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starOccultationDiagramDuplicateDays = 1e-10
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starOccultationDiagramGeometryArcsec = 0.05
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starOccultationDiagramPositionDeg = 0.01
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)
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// StarOccultationDiagramOptions 控制本地恒星月掩图的轨迹采样。
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// StarOccultationDiagramOptions controls local stellar-occultation diagram sampling.
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type StarOccultationDiagramOptions struct {
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// StepDays 是请求的轨迹采样步长，单位为日；非正值或非有限值使用两分钟，正值小于一秒时使用一秒。长事件可能增大实际步长，使基础轨迹不超过 2000 个采样点；必要阶段帧仍会额外保留。结果会报告实际采用的值。
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// StepDays is the requested track sampling step in days. Non-positive or non-finite values use two minutes, and positive values below one second use one second. Long events may increase the effective step to keep the base track within 2000 samples; required phase frames are retained in addition. The result reports the effective value.
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StepDays float64
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}
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// StarOccultationDiagramFrame 描述一个时刻的站心月球与恒星几何。
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// StarOccultationDiagramFrame describes topocentric Moon-star geometry at one instant.
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type StarOccultationDiagramFrame struct {
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// JDE 是 TT 儒略历书日。
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// JDE is the TT Julian ephemeris day.
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JDE float64
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// StarXArcsec 和 StarYArcsec 是相对月心的切平面偏移，单位为角秒。X 向东为正，Y 向北为正。
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// StarXArcsec and StarYArcsec are tangent-plane offsets from the lunar center. X is positive east and Y is positive north.
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StarXArcsec float64
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StarYArcsec float64
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// MoonRadiusArcsec 是站心月球视半径，单位为角秒。
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// MoonRadiusArcsec is the topocentric apparent lunar semidiameter.
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MoonRadiusArcsec float64
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// SeparationArcsec 和 PositionAngleDeg 描述恒星相对月心的位置。
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// SeparationArcsec and PositionAngleDeg describe the star relative to the lunar center.
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SeparationArcsec float64
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PositionAngleDeg float64
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// MoonAltitudeDeg 和 MoonAzimuthDeg 是站心地平坐标。
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// MoonAltitudeDeg and MoonAzimuthDeg are topocentric horizontal coordinates.
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MoonAltitudeDeg float64
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MoonAzimuthDeg float64
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// BehindMoon 表示点光源恒星位于月缘内侧。
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// BehindMoon is true while the point-source star lies strictly inside the lunar limb.
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BehindMoon bool
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// Label 是主阶段标识；Labels 在掠掩事件中保留重合阶段。
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// Label is the primary key phase; Labels retains coincident phases for grazing events.
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Label string
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Labels []string
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}
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// StarOccultationDiagramResult 包含固定地点恒星月掩的几何数据。
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// StarOccultationDiagramResult contains geometry for a fixed-site stellar occultation.
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type StarOccultationDiagramResult struct {
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Occultation StarOccultationInfo
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Frames []StarOccultationDiagramFrame
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// StepDays 是实际采用的基础轨迹采样步长，单位为日。
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// StepDays is the effective base-track sampling step in days.
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StepDays float64
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}
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type starOccultationDiagramTime struct {
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jde float64
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labels []string
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}
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// StarOccultationDiagram 为已求解的固定地点恒星月掩计算以月心为原点的切平面轨迹。事件数据无效或不完整时，结果不含帧。
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// StarOccultationDiagram computes a Moon-centered tangent-plane track for an already solved fixed-site stellar occultation. Invalid or incomplete event data produces a result without frames.
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func StarOccultationDiagram(
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info StarOccultationInfo,
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star StarCoordinate,
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options StarOccultationDiagramOptions,
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) StarOccultationDiagramResult {
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options = normalizeStarOccultationDiagramOptions(options)
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result := StarOccultationDiagramResult{Occultation: info, StepDays: options.StepDays}
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if star.Validate() != nil || info.Observer.Validate() != nil ||
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!info.ContactsComplete || info.Immersion.IsZero() || info.Greatest.IsZero() || info.Emersion.IsZero() ||
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info.Greatest.Before(info.Immersion) || info.Emersion.Before(info.Greatest) ||
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(info.Type != OccultationTotal && info.Type != OccultationGrazing) {
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return result
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}
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startTT := occultationTimeToTT(info.Immersion)
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greatestTT := occultationTimeToTT(info.Greatest)
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endTT := occultationTimeToTT(info.Emersion)
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immersionFrame, immersionOK := starOccultationDiagramFrameAt(startTT, star, info.Observer)
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greatestFrame, greatestOK := starOccultationDiagramFrameAt(greatestTT, star, info.Observer)
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emersionFrame, emersionOK := starOccultationDiagramFrameAt(endTT, star, info.Observer)
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if !immersionOK || !greatestOK || !emersionOK ||
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!starOccultationDiagramMatchesInfo(info, immersionFrame, greatestFrame, emersionFrame) {
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return result
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}
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times, stepDays := starOccultationDiagramTimes(startTT, greatestTT, endTT, options.StepDays)
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result.StepDays = stepDays
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result.Frames = make([]StarOccultationDiagramFrame, 0, len(times))
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for _, item := range times {
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frame, ok := starOccultationDiagramFrameAt(item.jde, star, info.Observer)
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if !ok {
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return StarOccultationDiagramResult{Occultation: info, StepDays: stepDays}
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}
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frame.Labels = append([]string(nil), item.labels...)
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frame.Label = starOccultationDiagramPrimaryLabel(item.labels)
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result.Frames = append(result.Frames, frame)
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}
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return result
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}
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func starOccultationDiagramMatchesInfo(
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info StarOccultationInfo,
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immersion, greatest, emersion StarOccultationDiagramFrame,
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) bool {
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if !finite(info.MinimumSeparationArcsec) || !finite(info.MoonSemidiameterArcsec) ||
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!finite(info.PositionAngleDeg) {
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return false
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}
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if math.Abs(immersion.SeparationArcsec-immersion.MoonRadiusArcsec) > starOccultationDiagramGeometryArcsec ||
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math.Abs(emersion.SeparationArcsec-emersion.MoonRadiusArcsec) > starOccultationDiagramGeometryArcsec {
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return false
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}
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return math.Abs(greatest.SeparationArcsec-info.MinimumSeparationArcsec) <= starOccultationDiagramGeometryArcsec &&
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math.Abs(greatest.MoonRadiusArcsec-info.MoonSemidiameterArcsec) <= starOccultationDiagramGeometryArcsec &&
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math.Abs(signedAngleDifference(greatest.PositionAngleDeg, info.PositionAngleDeg)) <= starOccultationDiagramPositionDeg
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}
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func normalizeStarOccultationDiagramOptions(options StarOccultationDiagramOptions) StarOccultationDiagramOptions {
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if options.StepDays <= 0 || !finite(options.StepDays) {
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options.StepDays = starOccultationDiagramDefaultStepDays
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}
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if options.StepDays < starOccultationDiagramMinStepDays {
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options.StepDays = starOccultationDiagramMinStepDays
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}
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return options
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}
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func starOccultationDiagramTimes(startTT, greatestTT, endTT, stepDays float64) ([]starOccultationDiagramTime, float64) {
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if !finite(startTT) || !finite(greatestTT) || !finite(endTT) || greatestTT < startTT || endTT < greatestTT {
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return nil, stepDays
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}
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if endTT > startTT {
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if sampleCount := int(math.Ceil((endTT-startTT)/stepDays)) + 1; sampleCount > starOccultationDiagramMaxSamples {
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stepDays = (endTT - startTT) / float64(starOccultationDiagramMaxSamples-1)
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}
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}
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times := []starOccultationDiagramTime{
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{jde: startTT, labels: []string{"Immersion"}},
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{jde: greatestTT, labels: []string{"Greatest"}},
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{jde: endTT, labels: []string{"Emersion"}},
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}
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for jde := startTT + stepDays; jde < endTT; jde += stepDays {
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times = append(times, starOccultationDiagramTime{jde: jde})
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}
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sort.SliceStable(times, func(i, j int) bool {
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if times[i].jde == times[j].jde {
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return starOccultationDiagramLabelPriority(times[i].labels) < starOccultationDiagramLabelPriority(times[j].labels)
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}
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return times[i].jde < times[j].jde
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})
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return uniqueStarOccultationDiagramTimes(times), stepDays
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}
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func uniqueStarOccultationDiagramTimes(times []starOccultationDiagramTime) []starOccultationDiagramTime {
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unique := times[:0]
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for _, item := range times {
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if !finite(item.jde) {
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continue
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}
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if len(unique) == 0 || math.Abs(item.jde-unique[len(unique)-1].jde) > starOccultationDiagramDuplicateDays {
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item.labels = append([]string(nil), item.labels...)
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unique = append(unique, item)
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continue
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}
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unique[len(unique)-1].labels = mergeStarOccultationDiagramLabels(unique[len(unique)-1].labels, item.labels)
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}
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return unique
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}
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func mergeStarOccultationDiagramLabels(existing, incoming []string) []string {
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for _, label := range incoming {
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found := false
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for _, current := range existing {
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if current == label {
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found = true
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break
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}
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}
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if !found {
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existing = append(existing, label)
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}
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}
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return existing
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}
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func starOccultationDiagramPrimaryLabel(labels []string) string {
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for _, label := range labels {
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if label == "Greatest" {
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return label
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}
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}
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if len(labels) == 0 {
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return ""
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}
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return labels[0]
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}
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func starOccultationDiagramLabelPriority(labels []string) int {
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if len(labels) == 0 {
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return 99
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}
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switch labels[0] {
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case "Immersion":
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return 0
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case "Greatest":
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return 1
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case "Emersion":
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return 2
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default:
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return 99
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}
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}
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func starOccultationDiagramFrameAt(tt float64, star StarCoordinate, observer Observer) (StarOccultationDiagramFrame, bool) {
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position := starMoonPositionAt(tt, star, observer)
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moonRadius := moonTopocentricSemidiameterN(tt, observer, -1)
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if !position.valid || !finite(moonRadius) || moonRadius <= 0 {
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return StarOccultationDiagramFrame{}, false
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}
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separation := angularSeparationDegrees(position.moonRA, position.moonDec, position.starRA, position.starDec) * 3600
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positionAngle := occultationPositionAngle(position.moonRA, position.moonDec, position.starRA, position.starDec)
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if !finite(separation) || !finite(positionAngle) {
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return StarOccultationDiagramFrame{}, false
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}
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angle := positionAngle * math.Pi / 180
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return StarOccultationDiagramFrame{
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JDE: tt,
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StarXArcsec: separation * math.Sin(angle),
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StarYArcsec: separation * math.Cos(angle),
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MoonRadiusArcsec: moonRadius,
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SeparationArcsec: separation,
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PositionAngleDeg: positionAngle,
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MoonAltitudeDeg: occultationAltitude(tt, observer, position.moonRA, position.moonDec),
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MoonAzimuthDeg: occultationAzimuth(tt, observer, position.moonRA, position.moonDec),
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BehindMoon: separation < moonRadius-starOccultationGrazingTolerance,
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}, true
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}
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