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 svgmap 提供日食和月掩 SVG 共用的无国界 Natural Earth 地图 / Package svgmap provides the shared, border-free Natural Earth map used by
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// 日食、月食和月掩 SVG 渲染器共用 / eclipse and lunar-occultation SVG renderers.
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package svgmap
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import (
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_ "embed"
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"fmt"
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"math"
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"strings"
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"b612.me/astro/internal/geodata"
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)
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const (
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worldLandWidth = 5760
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worldLandHeight = 2880
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polarLandSize = 2880
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)
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// Projection 标识受支持的地图投影 / Projection identifies one of the supported map projections.
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type Projection = geodata.Projection
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const (
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ProjectionEquirectangular = geodata.ProjectionEquirectangular
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ProjectionNorthPolar = geodata.ProjectionNorthPolar
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ProjectionSouthPolar = geodata.ProjectionSouthPolar
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)
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// GeoPoint 是以度表示的地理点，东经为正 / GeoPoint is a geographic point in degrees, with east longitude positive.
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type GeoPoint = geodata.GeoPoint
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// Frame 描述一个投影地图在 SVG 画布中的位置 / Frame places one projected map in an SVG canvas.
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type Frame struct {
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X float64
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Y float64
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Width float64
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Height float64
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Projection Projection
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}
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//go:generate go run ./internal/mapgen -output-dir .
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//go:embed land_equirectangular.path
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var equirectangularLandPath string
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//go:embed land_north_polar.path
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var northPolarLandPath string
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//go:embed land_south_polar.path
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var southPolarLandPath string
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// ResolveProjection 校验显式投影，或为高纬事件选择极区视图 / ResolveProjection validates an explicit projection or selects a polar view
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// 为始终位于一个半球内的高纬事件选择极区视图 / for a high-latitude event that stays in one hemisphere.
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func ResolveProjection(requested Projection, focusLatitude, minimumLatitude, maximumLatitude float64) Projection {
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switch requested {
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case ProjectionEquirectangular, ProjectionNorthPolar, ProjectionSouthPolar:
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return requested
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}
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if focusLatitude >= 60 && minimumLatitude >= -2 {
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return ProjectionNorthPolar
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}
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if focusLatitude <= -60 && maximumLatitude <= 2 {
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return ProjectionSouthPolar
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}
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return ProjectionEquirectangular
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}
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// IsPolar 判断当前画布是否使用半球方位投影 / IsPolar reports whether the frame uses a hemispheric azimuthal projection.
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func (frame Frame) IsPolar() bool {
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return frame.Projection == ProjectionNorthPolar || frame.Projection == ProjectionSouthPolar
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}
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// Project 将经纬度映射为 SVG 坐标；布尔值为 false 表示点在极区投影半球外 / Project maps longitude and latitude to SVG coordinates. The boolean is false
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// 点位于极区投影的可见半球之外时返回 false / when a point lies outside a polar projection's visible hemisphere.
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func (frame Frame) Project(longitude, latitude float64) (float64, float64, bool) {
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if !frame.IsPolar() {
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x := frame.X + (longitude+180)/360*frame.Width
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y := frame.Y + (90-latitude)/180*frame.Height
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return x, y, true
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}
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hemisphere := frame.hemisphere()
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if latitude*hemisphere < -1e-9 {
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return 0, 0, false
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}
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radius := (90 - hemisphere*latitude) / 90 * math.Min(frame.Width, frame.Height) / 2
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angle := longitude * math.Pi / 180
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return frame.X + frame.Width/2 + radius*math.Sin(angle),
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frame.Y + frame.Height/2 - radius*math.Cos(angle), true
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}
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// ClipDefinition 写入地图的矩形或圆形裁剪路径 / ClipDefinition writes the rectangular or circular clipping path for a map.
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func (frame Frame) ClipDefinition(id string) string {
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if frame.IsPolar() {
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return fmt.Sprintf(`<clipPath id="%s"><circle cx="%.3f" cy="%.3f" r="%.3f"/></clipPath>`,
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id, frame.X+frame.Width/2, frame.Y+frame.Height/2, math.Min(frame.Width, frame.Height)/2)
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}
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return fmt.Sprintf(`<clipPath id="%s"><rect x="%.3f" y="%.3f" width="%.3f" height="%.3f"/></clipPath>`,
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id, frame.X, frame.Y, frame.Width, frame.Height)
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}
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// WriteOcean 绘制地图的物理范围 / WriteOcean renders the map's physical extent.
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func (frame Frame) WriteOcean(builder *strings.Builder) {
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if frame.IsPolar() {
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fmt.Fprintf(builder, `<circle class="map-ocean" cx="%.3f" cy="%.3f" r="%.3f" fill="#edf3f2"/>`,
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frame.X+frame.Width/2, frame.Y+frame.Height/2, math.Min(frame.Width, frame.Height)/2)
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return
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}
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fmt.Fprintf(builder, `<rect class="map-ocean" x="%.3f" y="%.3f" width="%.3f" height="%.3f" fill="#edf3f2"/>`,
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frame.X, frame.Y, frame.Width, frame.Height)
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}
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// WriteGraticule 绘制符合投影的经线和纬线 / WriteGraticule renders projection-correct meridians and parallels.
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func (frame Frame) WriteGraticule(builder *strings.Builder, clipID string) {
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fmt.Fprintf(builder, `<g class="graticule" clip-path="url(#%s)" fill="none" stroke="#b8c4c3" stroke-width="0.65">`, clipID)
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if !frame.IsPolar() {
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for longitude := -150.0; longitude <= 150; longitude += 30 {
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x, _, _ := frame.Project(longitude, 0)
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fmt.Fprintf(builder, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f"/>`, x, frame.Y, x, frame.Y+frame.Height)
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}
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for latitude := -60.0; latitude <= 60; latitude += 30 {
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_, y, _ := frame.Project(0, latitude)
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fmt.Fprintf(builder, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f"/>`, frame.X, y, frame.X+frame.Width, y)
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}
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} else {
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centerX := frame.X + frame.Width/2
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centerY := frame.Y + frame.Height/2
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radius := math.Min(frame.Width, frame.Height) / 2
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for _, fraction := range []float64{1.0 / 3, 2.0 / 3, 1} {
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fmt.Fprintf(builder, `<circle cx="%.3f" cy="%.3f" r="%.3f"/>`, centerX, centerY, radius*fraction)
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}
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for longitude := -150.0; longitude <= 180; longitude += 30 {
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x, y, _ := frame.Project(longitude, 0)
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fmt.Fprintf(builder, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f"/>`, centerX, centerY, x, y)
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}
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}
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builder.WriteString(`</g>`)
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}
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// WriteLand 绘制无国界的 Natural Earth 1:50m 陆地 / WriteLand renders Natural Earth 1:50m physical land without borders.
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func (frame Frame) WriteLand(builder *strings.Builder, clipID string) {
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path := equirectangularLandPath
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viewWidth := float64(worldLandWidth)
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viewHeight := float64(worldLandHeight)
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if frame.Projection == ProjectionNorthPolar {
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path = northPolarLandPath
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viewWidth, viewHeight = polarLandSize, polarLandSize
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} else if frame.Projection == ProjectionSouthPolar {
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path = southPolarLandPath
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viewWidth, viewHeight = polarLandSize, polarLandSize
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}
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fmt.Fprintf(builder, `<g class="land-layer" clip-path="url(#%s)" fill="#d8d9d2" stroke="#a6aaa4" stroke-width="0.75" stroke-linejoin="round"><path class="land" d="`, clipID)
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builder.WriteString(path)
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fmt.Fprintf(builder, `" transform="matrix(%.9f 0 0 %.9f %.3f %.3f)" fill-rule="evenodd" vector-effect="non-scaling-stroke"/></g>`,
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frame.Width/viewWidth, frame.Height/viewHeight, frame.X, frame.Y)
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}
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// WriteFrame 绘制地图轮廓 / WriteFrame renders the map outline.
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func (frame Frame) WriteFrame(builder *strings.Builder) {
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if frame.IsPolar() {
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fmt.Fprintf(builder, `<circle class="map-frame" cx="%.3f" cy="%.3f" r="%.3f" fill="none" stroke="#707879" stroke-width="1.1"/>`,
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frame.X+frame.Width/2, frame.Y+frame.Height/2, math.Min(frame.Width, frame.Height)/2)
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return
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}
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fmt.Fprintf(builder, `<rect class="map-frame" x="%.3f" y="%.3f" width="%.3f" height="%.3f" fill="none" stroke="#707879" stroke-width="1.1"/>`,
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frame.X, frame.Y, frame.Width, frame.Height)
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}
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// PolylineSegments 将地理折线裁剪到选定投影并 / PolylineSegments clips a geographic polyline to the selected projection and
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// 在等经纬投影中按日界线拆分路径 / splits equirectangular paths at the antimeridian.
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func PolylineSegments(points []GeoPoint, projection Projection) [][]GeoPoint {
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return geodata.PolylineSegments(points, projection)
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}
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// PolygonFragments 将地理多边形裁剪到选定地图范围 / PolygonFragments clips a geographic polygon to the selected map extent.
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func PolygonFragments(points []GeoPoint, projection Projection) [][]GeoPoint {
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return geodata.PolygonFragments(points, projection)
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}
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func (frame Frame) hemisphere() float64 {
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if frame.Projection == ProjectionSouthPolar {
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return -1
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}
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return 1
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}
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