feat: 完善时标与天象几何计算并扩展输出接口

- 新增时标、ΔT 模型、质心时间与 UT1 支持
- 改进日月食、月掩、行星事件及路径边界计算
- 完善恒星三维自行与动态距离传播
- 扩展 SVG、GeoJSON、KML 输出与底层距离换算工具
- 整理中英文手册、示例资源及回归测试

internal/svgmap/map.go

@@ -163,11 +163,13 @@ func (frame Frame) WriteGraticule(builder *strings.Builder, clipID string) {
 	}
 	fmt.Fprintf(builder, `<g class="graticule" clip-path="url(#%s)" fill="none" stroke="#b8c4c3" stroke-width="0.65">`, clipID)
 	if !frame.IsPolar() {
-		first, last := -150.0, 150.0
+		// 居中视图循环到窗口另一端会同一条接缝经线，只画一次。
+		first, count := -150.0, 11
 		if frame.CenterLongitude != 0 {
-			first, last = frame.CenterLongitude-180, frame.CenterLongitude+180
+			first, count = frame.CenterLongitude-180, 12
 		}
-		for longitude := first; longitude <= last; longitude += 30 {
+		for index := 0; index < count; index++ {
+			longitude := first + 30*float64(index)
 			x, _, _ := frame.Project(longitude, 0)
 			if frame.CenterLongitude != 0 && (x < frame.X-0.5 || x > frame.X+frame.Width+0.5) {
 				continue
@@ -269,17 +271,18 @@ func (frame Frame) hemisphere() float64 {
 	return 1
 }
 
-// equirectangularLongitudeOffset 返回经度相对居中经线的偏移，换算成 0…360 的剂量。
-// 居中经线落在画面正中，其对面的经线落在左右任一边界上。
+// equirectangularLongitudeOffset 返回经度相对画面左边缘的偏移，换算成 0…360 的剂量。
+// 居中经线落在画面正中，其对面的经线同时是左右边缘：已经在窗口内的经度按原值返回，
+// 让接缝两侧的点各自贴住自己那一侧的边缘，窗口外的经度再按 360 折回。
 func equirectangularLongitudeOffset(longitude, center float64) float64 {
-	offset := math.Mod(longitude-center, 360)
+	offset := longitude - (center - 180)
+	if offset >= 0 && offset <= 360 {
+		return offset
+	}
+	offset = math.Mod(offset, 360)
 	if offset < 0 {
 		offset += 360
 	}
-	offset += 180
-	if offset >= 360 {
-		offset -= 360
-	}
 	return offset
 }
 

internal/svgmap/seam_test.go

@@ -0,0 +1,92 @@
+package svgmap
+
+import (
+	"math"
+	"testing"
+)
+
+// 居中经线对面的接缝同时是画面左右边缘：贴右边缘的分段必须落在窗口右端，
+// 折回左端会让闭合边横穿整幅图。
+func TestEquirectangularSeamKeepsBothWindowEdges(t *testing.T) {
+	frame := Frame{X: 52, Y: 168, Width: 610.8, Height: 305.4,
+		Projection: ProjectionEquirectangular, CenterLongitude: 176.271}
+	left := frame.CenterLongitude - 180
+	right := frame.CenterLongitude + 180
+	if x, _, _ := frame.Project(left, 0); math.Abs(x-frame.X) > 1e-9 {
+		t.Fatalf("seam at the left edge maps to x=%.6f, want %.6f", x, frame.X)
+	}
+	if x, _, _ := frame.Project(right, 0); math.Abs(x-(frame.X+frame.Width)) > 1e-9 {
+		t.Fatalf("the same seam in the adjacent world maps to x=%.6f, want %.6f", x, frame.X+frame.Width)
+	}
+	if x, _, _ := frame.Project(right-0.5, 0); x >= frame.X+frame.Width {
+		t.Fatalf("a point just west of the seam maps to x=%.6f, want inside the frame", x)
+	}
+
+	ring := make([]GeoPoint, 0, 40)
+	for longitude := -10.0; longitude <= 5; longitude += 5 {
+		ring = append(ring, GeoPoint{Longitude: longitude, Latitude: 0})
+	}
+	for latitude := 5.0; latitude <= 20; latitude += 5 {
+		ring = append(ring, GeoPoint{Longitude: 5, Latitude: latitude})
+	}
+	for longitude := 0.0; longitude >= -10; longitude -= 5 {
+		ring = append(ring, GeoPoint{Longitude: longitude, Latitude: 20})
+	}
+	for latitude := 15.0; latitude >= 5; latitude -= 5 {
+		ring = append(ring, GeoPoint{Longitude: -10, Latitude: latitude})
+	}
+	fragments := PolygonFragments(ring, frame.Clip())
+	if len(fragments) != 2 {
+		t.Fatalf("straddling ring fragments = %d, want 2", len(fragments))
+	}
+	for index, fragment := range fragments {
+		minX, maxX := math.Inf(1), math.Inf(-1)
+		for _, point := range fragment {
+			x, _, ok := frame.Project(point.Longitude, point.Latitude)
+			if !ok {
+				t.Fatalf("fragment %d dropped a point", index)
+			}
+			minX, maxX = math.Min(minX, x), math.Max(maxX, x)
+		}
+		if maxX-minX > frame.Width/2 {
+			t.Fatalf("fragment %d spans %.3f px, want one side of the seam only", index, maxX-minX)
+		}
+	}
+}
+
+// 绕极点一圈的环靠地图上边缘闭合，闭合边两端必须分贴左右边缘。
+func TestEquirectangularPoleClosureUsesMapEdges(t *testing.T) {
+	frame := Frame{X: 52, Y: 168, Width: 610.8, Height: 305.4,
+		Projection: ProjectionEquirectangular, CenterLongitude: 176.271}
+	ring := make([]GeoPoint, 0, 36)
+	for longitude := -180.0; longitude < 180; longitude += 10 {
+		ring = append(ring, GeoPoint{Longitude: longitude, Latitude: 70})
+	}
+	fragments := PolygonFragments(ring, frame.Clip())
+	if len(fragments) != 1 {
+		t.Fatalf("cap ring fragments = %d, want 1", len(fragments))
+	}
+	left, right, top := false, false, false
+	for _, point := range fragments[0] {
+		if math.Abs(point.Latitude) < 89.999 {
+			continue
+		}
+		x, y, _ := frame.Project(point.Longitude, point.Latitude)
+		if math.Abs(y-frame.Y) > 1e-6 {
+			t.Fatalf("pole closure at y=%.3f, want the map top edge %.3f", y, frame.Y)
+		}
+		switch {
+		case math.Abs(x-frame.X) < 1e-6:
+			left = true
+		case math.Abs(x-(frame.X+frame.Width)) < 1e-6:
+			right = true
+		}
+		top = true
+	}
+	if !top || !left || !right {
+		t.Fatalf("pole closure left=%v right=%v top=%v, want the cap closed along both edges", left, right, top)
+	}
+	if fragments := PolygonFragments(ring, ClipView{Projection: ProjectionEquirectangular}); len(fragments) != 1 {
+		t.Fatalf("uncentred cap fragments = %d, want 1", len(fragments))
+	}
+}