79 lines
3.0 KiB
Go
79 lines
3.0 KiB
Go
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package basic
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import "math"
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// PlanetTransitVisibilityColumn 子午线上的可见纬度区间，端点单位为度 / visible latitude intervals on a meridian, in degrees.
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type PlanetTransitVisibilityColumn struct {
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Longitude float64
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Intervals [][2]float64
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}
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// PlanetTransitVisibilityColumnsWithInstance 按 2° 经度、1° 纬度探测站心可见区并细化边界 / sample topocentric visibility at 2-degree longitude and 1-degree latitude spacing and refine boundaries.
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func PlanetTransitVisibilityColumnsWithInstance(transit PlanetTransitResult, inst *Instance) []PlanetTransitVisibilityColumn {
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snapshot, ok := newPlanetTransitSnapshot(transit, inst)
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if !ok {
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return nil
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}
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snapshot.visibilityOnce.Do(func() {
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for column := 0; column <= 180; column++ {
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longitude := -180 + float64(column)*2
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visible := func(latitude float64) bool {
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local := snapshot.local(transit, Observer{Longitude: longitude, Latitude: latitude})
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return local.Valid && local.Visible
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}
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value := PlanetTransitVisibilityColumn{Longitude: longitude}
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previous, start := visible(-90), -90.0
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for latitude := -89.0; latitude <= 90; latitude++ {
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current := visible(latitude)
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if current != previous {
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left, right := latitude-1, latitude
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for right-left > 0.0001 {
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middle := (left + right) / 2
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if visible(middle) == previous {
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left = middle
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} else {
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right = middle
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}
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}
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boundary := (left + right) / 2
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if current {
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start = boundary
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} else {
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value.Intervals = append(value.Intervals, [2]float64{start, boundary})
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}
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}
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previous = current
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}
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if previous {
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value.Intervals = append(value.Intervals, [2]float64{start, 90})
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}
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snapshot.visibility = append(snapshot.visibility, value)
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}
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})
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result := make([]PlanetTransitVisibilityColumn, len(snapshot.visibility))
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for index, column := range snapshot.visibility {
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result[index] = PlanetTransitVisibilityColumn{Longitude: column.Longitude, Intervals: append([][2]float64(nil), column.Intervals...)}
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}
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return result
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}
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// PlanetTransitVisibilityPolygonsWithInstance 可见区的经度条带多边形 / longitude-strip polygons of the visible region.
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func PlanetTransitVisibilityPolygonsWithInstance(transit PlanetTransitResult, inst *Instance) [][]PlanetTransitIsochronePoint {
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columns := PlanetTransitVisibilityColumnsWithInstance(transit, inst)
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var result [][]PlanetTransitIsochronePoint
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for index := 1; index < len(columns); index++ {
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left, right := columns[index-1], columns[index]
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for _, interval := range left.Intervals {
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for _, other := range right.Intervals {
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if math.Min(interval[1], other[1]) <= math.Max(interval[0], other[0]) {
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continue
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}
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result = append(result, []PlanetTransitIsochronePoint{
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{Longitude: left.Longitude, Latitude: interval[0]}, {Longitude: right.Longitude, Latitude: other[0]},
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{Longitude: right.Longitude, Latitude: other[1]}, {Longitude: left.Longitude, Latitude: interval[1]},
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})
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}
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}
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}
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return result
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}
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