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

moon/svg/occultation_time_labels.go

@@ -0,0 +1,157 @@
+package svg
+
+import (
+	"fmt"
+	"html"
+	"math"
+	"strings"
+	"time"
+
+	"b612.me/astro/moon"
+)
+
+func writeOccultationTimeMarkers(
+	b *strings.Builder,
+	points []moon.OccultationPathPoint,
+	layout starOccultationSVGLayout,
+	options StarOccultationSVGOptions,
+	excluded []time.Time,
+	greatest time.Time,
+) {
+	if options.TimeLabelStep <= 0 || len(points) < 2 {
+		return
+	}
+	markers := occultationTimeMarkerPoints(points, options.TimeLabelStep, options.Location, excluded)
+	frame := layout.mapFrame()
+	projected := make([][2]float64, 0, len(markers))
+	for _, marker := range markers {
+		if marker.MoonAltitude < 0 {
+			continue
+		}
+		x, y, visible := frame.Project(marker.Longitude, marker.Latitude)
+		if !visible || x < frame.X+22 || x > frame.X+frame.Width-22 || y < frame.Y+12 || y > frame.Y+frame.Height-12 {
+			continue
+		}
+		tooClose := false
+		for _, previous := range projected {
+			if math.Hypot(x-previous[0], y-previous[1]) < 44 {
+				tooClose = true
+				break
+			}
+		}
+		if tooClose {
+			continue
+		}
+		projected = append(projected, [2]float64{x, y})
+		labelY := y - 8
+		if occultationTimesNear(marker.Time, greatest, occultationGreatestTimeLabelWindow(options.TimeLabelStep)) {
+			labelY = y + 15
+		} else if labelY < frame.Y+10 {
+			labelY = y + 15
+		}
+		fmt.Fprintf(b, `<g class="occultation-time-marker"><circle cx="%.3f" cy="%.3f" r="2.3" fill="#087f8c" stroke="#ffffff" stroke-width="1"/><text x="%.3f" y="%.3f" fill="#075f69" stroke="#ffffff" stroke-width="3" paint-order="stroke" font-family="Arial, sans-serif" font-size="9" font-weight="700" text-anchor="middle">%s</text></g>`,
+			x, y, x, labelY, html.EscapeString(marker.Time.In(options.Location).Format("15:04")))
+	}
+}
+
+func occultationGreatestTimeLabelWindow(step time.Duration) time.Duration {
+	window := step / 3
+	if window < 10*time.Minute {
+		return 10 * time.Minute
+	}
+	return window
+}
+
+func occultationTimeMarkerPoints(
+	points []moon.OccultationPathPoint,
+	step time.Duration,
+	location *time.Location,
+	excluded []time.Time,
+) []moon.OccultationPathPoint {
+	if len(points) < 2 || step <= 0 {
+		return nil
+	}
+	start := points[0].Time
+	end := points[len(points)-1].Time
+	current := firstOccultationTimeLabelAfter(start, step, location)
+	window := step / 4
+	if window > 5*time.Minute {
+		window = 5 * time.Minute
+	}
+	if window < 30*time.Second {
+		window = 30 * time.Second
+	}
+	result := make([]moon.OccultationPathPoint, 0)
+	segment := 1
+	for current.Before(end) {
+		for segment < len(points) && points[segment].Time.Before(current) {
+			segment++
+		}
+		if segment >= len(points) {
+			break
+		}
+		if !occultationTimeNearAny(current, excluded, window) {
+			a, next := points[segment-1], points[segment]
+			span := next.Time.Sub(a.Time)
+			if span > 0 {
+				fraction := float64(current.Sub(a.Time)) / float64(span)
+				result = append(result, interpolateOccultationTimeMarker(a, next, fraction, current))
+			}
+		}
+		current = current.Add(step)
+	}
+	return result
+}
+
+func interpolateOccultationTimeMarker(
+	a, b moon.OccultationPathPoint,
+	fraction float64,
+	value time.Time,
+) moon.OccultationPathPoint {
+	deltaLongitude := b.Longitude - a.Longitude
+	if deltaLongitude > 180 {
+		deltaLongitude -= 360
+	} else if deltaLongitude < -180 {
+		deltaLongitude += 360
+	}
+	longitude := a.Longitude + fraction*deltaLongitude
+	if longitude > 180 {
+		longitude -= 360
+	} else if longitude < -180 {
+		longitude += 360
+	}
+	point := starOccultationInterpolatePathPoint(a, b, fraction, longitude)
+	point.Time = value
+	return point
+}
+
+func firstOccultationTimeLabelAfter(value time.Time, step time.Duration, location *time.Location) time.Time {
+	local := value.In(location)
+	dayStart := time.Date(local.Year(), local.Month(), local.Day(), 0, 0, 0, 0, location)
+	elapsed := local.Sub(dayStart)
+	return dayStart.Add((elapsed/step + 1) * step)
+}
+
+func occultationTimeNearAny(value time.Time, excluded []time.Time, window time.Duration) bool {
+	for _, candidate := range excluded {
+		if candidate.IsZero() {
+			continue
+		}
+		delta := value.Sub(candidate)
+		if delta < 0 {
+			delta = -delta
+		}
+		if delta <= window {
+			return true
+		}
+	}
+	return false
+}
+
+func occultationTimesNear(a, b time.Time, window time.Duration) bool {
+	delta := a.Sub(b)
+	if delta < 0 {
+		delta = -delta
+	}
+	return delta <= window
+}