Files
astro/eclipse/svg/transit_local.go
b612 ccf5880269 feat: 完善水星与金星全球凌日搜索及制图导出
- 基于平均下合周期与节点相位预筛候选,减少无效星历计算;跳过无法求解的单个会合周期,避免有限覆盖星历导致搜索提前终止
- 引入影轴 γ、半影半径及地球尺度几何判定,结合站心可见性识别地心无接触、仅部分地区可见的掠凌
- 添加金星 243 年、水星 46 年周期族编号,并明确编号适用范围及未分配时的零值语义
- 为 SVG、GeoJSON 和 KML 增加站心部分凌日可见区,适配接触等时线、几何元数据、图层样式及取景;为地心无接触凌日事件增加正射图,按可见区球面面积加权居中
2026-10-20 22:35:39 +08:00

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package svg
import (
"fmt"
"html"
"math"
"strings"
"time"
"b612.me/astro"
"b612.me/astro/basic"
"b612.me/astro/internal/svgchart"
"b612.me/astro/internal/timenote"
)
const (
transitLocalDefaultWidth = 960
transitLocalDefaultHeight = 680
)
// TransitLocalSVGOptions 控制站心凌日日面图。
// TransitLocalSVGOptions controls a topocentric planetary-transit solar-disk chart.
type TransitLocalSVGOptions struct {
// Width 和 Height 是 SVG 画布尺寸;宽度小于 640 或高度小于 480 时使用 960x680 默认值。
// Width and Height are SVG canvas dimensions. Width values below 640 and height values below 480 use the 960x680 defaults.
Width int
Height int
// Step 是行星轨迹采样步长;非正值使用两分钟。
// Step is the planet-track sampling step. Non-positive values use two minutes.
Step time.Duration
// Language 为 "en"(不区分大小写)时使用英文,否则使用中文。
// Language uses English for "en" (case-insensitive) and Chinese otherwise.
Language string
// Location 控制显示的事件时刻;nil 使用 date.Location()。
// Location controls displayed event times. Nil uses date.Location().
Location *time.Location
// TimeScale 选择图中时刻的时标:零值 UTC;TimeScaleUT1 要求 Location 为 nil 或 UTC,否则返回 false。
// TimeScale selects the label scale: the zero value is UTC; TimeScaleUT1 requires Location to be nil or UTC, otherwise the renderer returns false.
TimeScale astro.TimeScale
// 空文本字段使用本地化的自动标签。
// Empty text fields use localized automatic labels.
Title string
FooterNote string
}
// TransitLocalSVG 绘制距 date 最近一次水星或金星凌日在观测地(经度 lon、纬度 lat,东经北纬为正,海拔 height 米)
// 的站心日面图:上北左东的天空视向,画出行星中心轨迹、各接触与凌甚时的行星圆面,以及接触时刻表。
// 轨迹上太阳中心在视地平下(计入标准大气折射)的部分画成灰色虚线。该地几何上看不到凌日、找不到凌日或选项无效时返回 false。
// TransitLocalSVG renders the topocentric solar-disk view of the Mercury or Venus transit closest to date, seen from
// longitude lon and latitude lat (east and north positive) at height metres: north up and east left as on the sky, with
// the planet-centre track, the planet disk at each contact and at greatest, and a contact table. Track parts where the
// Sun's centre is below the apparent horizon (standard refraction) are drawn grey and dashed. It returns false when the
// site sees no geometric transit, no transit is found or the options are invalid.
func TransitLocalSVG(planet TransitPlanet, date time.Time, lon, lat, height float64, options TransitLocalSVGOptions) (string, bool) {
transit, ok := closestPlanetTransit(planet, date)
if !ok {
return "", false
}
if options.TimeScale == astro.TimeScaleUT1 {
if options.Location != nil && options.Location != time.UTC {
return "", false
}
options.Location = time.UTC
}
local := basic.PlanetTransitLocal(transit, basic.Observer{Longitude: lon, Latitude: lat, Height: height})
if !local.Valid {
return "", false
}
if options.Step <= 0 {
options.Step = 2 * time.Minute
}
frames := basic.PlanetTransitLocalFrames(transit, local, options.Step.Hours()/24)
if len(frames) < 2 {
return "", false
}
options = normalizeTransitLocalSVGOptions(date, options)
return renderTransitLocalSVG(planet, local, frames, options), true
}
func normalizeTransitLocalSVGOptions(date time.Time, options TransitLocalSVGOptions) TransitLocalSVGOptions {
if options.Width < 640 {
options.Width = transitLocalDefaultWidth
}
if options.Height < 480 {
options.Height = transitLocalDefaultHeight
}
if strings.EqualFold(options.Language, "en") {
options.Language = "en"
} else {
options.Language = "zh"
}
if options.Location == nil {
options.Location = date.Location()
}
return options
}
// transitLocalEvent 是日面上标注的一个接触或凌甚。
type transitLocalEvent struct {
label, name string
contact basic.PlanetTransitLocalContact
separation float64
}
func transitLocalEvents(local basic.PlanetTransitLocalResult, language string) []transitLocalEvent {
names := []string{"一触", "二触", "凌甚", "三触", "四触"}
if language == "en" {
names = []string{"C1", "C2", "Greatest", "C3", "C4"}
}
external := local.SunSemidiameterArcsec + local.PlanetSemidiameterArcsec
internal := local.SunSemidiameterArcsec - local.PlanetSemidiameterArcsec
candidates := []transitLocalEvent{
{"C1", names[0], local.ExternalIngress, external},
{"C2", names[1], local.InternalIngress, internal},
{"G", names[2], local.Greatest, local.MinimumSeparationArcsec},
{"C3", names[3], local.InternalEgress, internal},
{"C4", names[4], local.ExternalEgress, external},
}
events := candidates[:0]
for _, event := range candidates {
if event.contact.Valid {
events = append(events, event)
}
}
return events
}
// transitLocalSunUp 判断太阳中心几何高度 altitude 是否在视地平上(标准大气折射)。
func transitLocalSunUp(altitude float64) bool {
return altitude > -basic.RefractionFromApparentAltitude(0, transitMapRefractionPressureHPa, transitMapRefractionTemperatureC)
}
func transitDisplayTime(value time.Time, scale astro.TimeScale, location *time.Location) time.Time {
if value.IsZero() {
return value
}
if scale == astro.TimeScaleUT1 {
return basic.UT1FromUTC(value)
}
return value.In(location)
}
func renderTransitLocalSVG(
planet TransitPlanet,
local basic.PlanetTransitLocalResult,
frames []basic.PlanetTransitLocalFrame,
options TransitLocalSVGOptions,
) string {
width, height := float64(options.Width), float64(options.Height)
at := func(jd float64) time.Time {
return transitDisplayTime(basic.JD2DateByZone(jd, time.UTC, false), options.TimeScale, options.Location)
}
title := options.Title
if title == "" {
date := at(local.Greatest.JD).Format("2006-01-02")
if options.Language == "en" {
title = fmt.Sprintf("%s Transit of %s, Local Circumstances", date, transitMapPlanetName(planet, "en"))
} else {
title = fmt.Sprintf("%s %s凌日站心图", date, transitMapPlanetName(planet, "zh"))
}
}
site := transitLocalSiteText(local.Observer, options.Language)
summary := transitLocalSummaryText(local, options.Language)
var b strings.Builder
fmt.Fprintf(&b, `<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="%d" viewBox="0 0 %d %d" role="img" aria-label="%s">`,
options.Width, options.Height, options.Width, options.Height, html.EscapeString(title))
b.WriteString(`<defs><radialGradient id="transit-sun" cx="40%" cy="34%" r="64%"><stop offset="0%" stop-color="#fff8bb"/><stop offset="58%" stop-color="#ffd55f"/><stop offset="100%" stop-color="#f5a623"/></radialGradient></defs>`)
b.WriteString(`<rect width="100%" height="100%" fill="#efefed"/>`)
fmt.Fprintf(&b, `<rect x="22" y="18" width="%.3f" height="%.3f" fill="#ffffff" stroke="#c9c9c6" stroke-width="1.2"/>`, width-44, height-36)
titleText := title
if options.Title != "" {
titleText = svgchart.EllipsizeText(title, width-52, 24)
}
fmt.Fprintf(&b, `<text x="%.3f" y="47" fill="#111111" font-family="Georgia, 'Times New Roman', serif" font-size="24" font-weight="700" text-anchor="middle">%s</text>`,
width/2, html.EscapeString(titleText))
for index, line := range []string{site, summary} {
line = svgchart.EllipsizeText(line, width-80, 13)
fmt.Fprintf(&b, `<text x="%.3f" y="%.3f" fill="#333" font-family="Georgia, 'Times New Roman', serif" font-size="13" text-anchor="middle">%s</text>`,
width/2, 72+float64(index)*19, html.EscapeString(line))
}
// 日面区占左侧,接触表占右侧;日面半径要容下盘外的东南西北轴标签,所以上下界由副标题与页脚算出。
panelWidth := 300.0
footerLines := transitLocalFooterLines(local, options, width)
footerBaselines := transitLocalFooterBaselines(len(footerLines), height)
footerTop := height - 30.0
if len(footerBaselines) > 0 {
footerTop = footerBaselines[0] - 10.2
}
const (
headerBottom = 72 + 19 + 10 // 经纬度行、摘要行与留白
axisLabelAbove = 33.0 // 盘顶到“北”字上沿
axisLabelBelow = 36.0 // 盘底到“南”字下沿
minimumDiskHeight = 150.0
)
top, bottom := headerBottom+axisLabelAbove, footerTop-axisLabelBelow
if bottom-top < minimumDiskHeight {
shrink := (minimumDiskHeight - (bottom - top)) / 2
top -= shrink
bottom += shrink
}
diskLeft, diskRight := 46.0, width-panelWidth-60
cx, cy := (diskLeft+diskRight)/2, (top+bottom)/2
extent := local.SunSemidiameterArcsec + 2.2*local.PlanetSemidiameterArcsec + 60
scale := math.Min((diskRight-diskLeft)/2, (bottom-top)/2) / extent
mapX := func(x float64) float64 { return cx - x*scale } // 东在左
mapY := func(y float64) float64 { return cy - y*scale }
sunRadius := local.SunSemidiameterArcsec * scale
fmt.Fprintf(&b, `<circle class="transit-sun" cx="%.3f" cy="%.3f" r="%.3f" fill="url(#transit-sun)" stroke="#c78211" stroke-width="1.4"/>`, cx, cy, sunRadius)
writeTransitLocalAxes(&b, cx, cy, sunRadius, options.Language)
writeTransitLocalTrack(&b, frames, mapX, mapY)
events := transitLocalEvents(local, options.Language)
planetRadius := math.Max(local.PlanetSemidiameterArcsec*scale, 2)
table := &svgchart.LabelTable{}
table.Reserve(30, footerTop-4, width-60, height-footerTop+4)
table.Reserve(cx-14, cy+sunRadius+16, 28, 18)
table.Reserve(cx-14, cy-sunRadius-32, 28, 20)
for _, event := range events {
x, y := transitLocalEventPosition(frames, event.contact.JD, mapX, mapY)
fill, stroke := "#1d1d1d", "#000000"
if !transitLocalSunUp(event.contact.SunAltitudeDeg) {
fill, stroke = "#9a9a9a", "#6d6d6d"
}
fmt.Fprintf(&b, `<circle class="transit-planet-%s" cx="%.3f" cy="%.3f" r="%.3f" fill="%s" fill-opacity="0.92" stroke="%s" stroke-width="0.8"/>`,
strings.ToLower(event.label), x, y, planetRadius, fill, stroke)
table.Reserve(x-planetRadius, y-planetRadius, 2*planetRadius, 2*planetRadius)
}
for _, event := range events {
x, y := transitLocalEventPosition(frames, event.contact.JD, mapX, mapY)
// 标签放在远离日心的一侧,避开日面内的轨迹与圆面。
dx, dy := x-cx, y-cy
norm := math.Hypot(dx, dy)
if norm < 1e-6 {
dx, dy, norm = 0, -1, 1
}
text := event.name + " " + at(event.contact.JD).Format("15:04:05")
var placement svgchart.LabelPlacement
placed := false
// 相邻接触相隔仅数分钟时近处位次全被占,逐圈外推并画引线,不得丢标签。
for ring := 0; ring < 6 && !placed; ring++ {
offset := planetRadius + 12 + float64(ring)*16
candidates := []svgchart.LabelPlacement{}
for _, turn := range []float64{0, 0.5, -0.5, 1, -1} {
ux := dx/norm*math.Cos(turn) - dy/norm*math.Sin(turn)
uy := dx/norm*math.Sin(turn) + dy/norm*math.Cos(turn)
anchor := "start"
if ux < -0.3 {
anchor = "end"
} else if ux < 0.3 {
anchor = "middle"
}
candidate := svgchart.LabelPlacement{X: x + ux*offset, Y: y + uy*offset + 4, Anchor: anchor}
// 标签平移进白色图框内、接触表左侧,不能伸出画面。
box := svgchart.LabelTextBox(candidate.X, candidate.Y, 11, text, anchor)
candidate.X += math.Max(0, 30-box.X) - math.Max(0, box.X+box.Width-(width-panelWidth-44))
candidate.Y += math.Max(0, top-8-box.Y) - math.Max(0, box.Y+box.Height-(footerTop-4))
candidates = append(candidates, candidate)
}
placement, placed = table.Place(text, 11, candidates)
if placed && transitLocalLabelGap(placement, text, x, y) > planetRadius+16 {
// 引线连到标签框上离接触点最近的位置。
box := svgchart.LabelTextBox(placement.X, placement.Y, 11, text, placement.Anchor)
endX := math.Max(box.X, math.Min(x, box.X+box.Width))
endY := math.Max(box.Y, math.Min(y, box.Y+box.Height))
fmt.Fprintf(&b, `<line class="transit-event-leader" x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f" stroke="#555" stroke-width="0.7" opacity="0.7"/>`,
x, y, endX, endY)
}
}
if !placed {
continue
}
fmt.Fprintf(&b, `<text class="transit-event-label" x="%.3f" y="%.3f" fill="#222" stroke="#ffffff" stroke-width="2.6" paint-order="stroke" font-family="Arial, sans-serif" font-size="11" text-anchor="%s">%s</text>`,
placement.X, placement.Y, placement.Anchor, html.EscapeString(text))
}
tableWidth := panelWidth
tableX := width - panelWidth - 36
if minimum := cx + sunRadius + 40; tableX < minimum {
tableX = minimum
tableWidth = width - tableX - 36
}
writeTransitLocalContactTable(&b, local, events, at, tableX, top+10, tableWidth, options.Language)
writeTransitLocalFooter(&b, footerLines, footerBaselines)
b.WriteString(`</svg>`)
return b.String()
}
// transitLocalLabelGap 是接触点到标签框的最近距离。
func transitLocalLabelGap(placement svgchart.LabelPlacement, text string, x, y float64) float64 {
box := svgchart.LabelTextBox(placement.X, placement.Y, 11, text, placement.Anchor)
return math.Hypot(x-math.Max(box.X, math.Min(x, box.X+box.Width)), y-math.Max(box.Y, math.Min(y, box.Y+box.Height)))
}
func transitLocalSiteText(observer basic.Observer, language string) string {
ew, ns := "E", "N"
if language != "en" {
ew, ns = "东经", "北纬"
}
lon, lat := observer.Longitude, observer.Latitude
if lon < 0 {
ew = map[bool]string{true: "W", false: "西经"}[language == "en"]
lon = -lon
}
if lat < 0 {
ns = map[bool]string{true: "S", false: "南纬"}[language == "en"]
lat = -lat
}
if language == "en" {
return fmt.Sprintf("Site %.4f°%s %.4f°%s, height %.0f m", lon, ew, lat, ns, observer.Height)
}
return fmt.Sprintf("观测地 %s %.4f° %s %.4f°,海拔 %.0f 米", ew, lon, ns, lat, observer.Height)
}
func transitLocalSummaryText(local basic.PlanetTransitLocalResult, language string) string {
kind := map[bool]string{true: "完整凌日", false: "掠凌(无内切接触)"}[local.HasInternal]
visible := map[bool]string{true: "可见", false: "全程太阳在地平下"}[local.Visible]
if language == "en" {
kind = map[bool]string{true: "full transit", false: "grazing transit (no internal contacts)"}[local.HasInternal]
visible = map[bool]string{true: "visible", false: "Sun below the horizon throughout"}[local.Visible]
return fmt.Sprintf("Topocentric %s, %s | minimum separation %.1f″ | Sun %.1f″ | planet %.2f″",
kind, visible, local.MinimumSeparationArcsec, local.SunSemidiameterArcsec, local.PlanetSemidiameterArcsec)
}
return fmt.Sprintf("站心%s,%s | 最小角距 %.1f″ | 太阳视半径 %.1f″ | 行星视半径 %.2f″",
kind, visible, local.MinimumSeparationArcsec, local.SunSemidiameterArcsec, local.PlanetSemidiameterArcsec)
}
// writeTransitLocalAxes 画过日心的南北、东西虚线与方向字。
func writeTransitLocalAxes(b *strings.Builder, cx, cy, radius float64, language string) {
reach := radius + 12
fmt.Fprintf(b, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f" stroke="#8b6a2b" stroke-width="0.8" stroke-dasharray="3 4" stroke-opacity="0.7"/>`, cx, cy-reach, cx, cy+reach)
fmt.Fprintf(b, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f" stroke="#8b6a2b" stroke-width="0.8" stroke-dasharray="3 4" stroke-opacity="0.7"/>`, cx-reach, cy, cx+reach, cy)
labels := [4]string{"北", "南", "东", "西"}
if language == "en" {
labels = [4]string{"N", "S", "E", "W"}
}
for index, item := range []struct{ x, y float64 }{
{cx, cy - reach - 6}, {cx, cy + reach + 16}, {cx - reach - 12, cy + 5}, {cx + reach + 12, cy + 5},
} {
fmt.Fprintf(b, `<text x="%.3f" y="%.3f" fill="#6b5222" font-family="Georgia, 'Times New Roman', serif" font-size="13" text-anchor="middle">%s</text>`,
item.x, item.y, labels[index])
}
}
// writeTransitLocalTrack 画行星中心轨迹:太阳在视地平上的段为实线,地平下为灰色虚线。
func writeTransitLocalTrack(b *strings.Builder, frames []basic.PlanetTransitLocalFrame, mapX, mapY func(float64) float64) {
start := 0
for index := 1; index <= len(frames); index++ {
if index < len(frames) && transitLocalSunUp(frames[index].SunAltitudeDeg) == transitLocalSunUp(frames[start].SunAltitudeDeg) {
continue
}
// 段尾取下一段首点,相邻两段首尾相接。
end := index
if end == len(frames) {
end--
}
class, color, dash := "transit-track", "#24518a", "none"
if !transitLocalSunUp(frames[start].SunAltitudeDeg) {
class, color, dash = "transit-track-below-horizon", "#8a8a8a", "5 4"
}
fmt.Fprintf(b, `<path class="%s" d="`, class)
for position := start; position <= end; position++ {
command := "L"
if position == start {
command = "M"
}
fmt.Fprintf(b, `%s %.3f %.3f `, command, mapX(frames[position].PlanetXArcsec), mapY(frames[position].PlanetYArcsec))
}
fmt.Fprintf(b, `" fill="none" stroke="%s" stroke-width="1.4" stroke-dasharray="%s" stroke-linecap="round"/>`, color, dash)
start = index
}
}
// transitLocalEventPosition 取时刻最接近 jd 的采样帧位置;接触与凌甚时刻本身在采样里。
func transitLocalEventPosition(frames []basic.PlanetTransitLocalFrame, jd float64, mapX, mapY func(float64) float64) (float64, float64) {
best := 0
for index := range frames {
if math.Abs(frames[index].JD-jd) < math.Abs(frames[best].JD-jd) {
best = index
}
}
return mapX(frames[best].PlanetXArcsec), mapY(frames[best].PlanetYArcsec)
}
func writeTransitLocalContactTable(
b *strings.Builder,
local basic.PlanetTransitLocalResult,
events []transitLocalEvent,
at func(float64) time.Time,
x, y, width float64,
language string,
) {
heading := [4]string{"接触时刻", "时刻", "太阳高度", "方位"}
if language == "en" {
heading = [4]string{"Contacts", "Time", "Sun alt.", "Az."}
}
fmt.Fprintf(b, `<text x="%.3f" y="%.3f" fill="#111" font-family="Georgia, 'Times New Roman', serif" font-size="15" font-weight="700">%s</text>`, x, y, heading[0])
columns := []float64{x, x + 78, x + 176, x + 252}
rowY := y + 26
for index, text := range []string{"", heading[1], heading[2], heading[3]} {
fmt.Fprintf(b, `<text x="%.3f" y="%.3f" fill="#555" font-family="Arial, sans-serif" font-size="11">%s</text>`, columns[index], rowY, text)
}
fmt.Fprintf(b, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f" stroke="#bbb" stroke-width="0.8"/>`, x, rowY+6, x+width-8, rowY+6)
for _, event := range events {
rowY += 22
fill := "#222"
if !transitLocalSunUp(event.contact.SunAltitudeDeg) {
fill = "#8a8a8a"
}
cells := []string{
event.name,
at(event.contact.JD).Format("15:04:05"),
fmt.Sprintf("%+.1f°", event.contact.SunAltitudeDeg),
fmt.Sprintf("%.1f°", event.contact.SunAzimuthDeg),
}
for index, text := range cells {
fmt.Fprintf(b, `<text class="transit-contact-row" x="%.3f" y="%.3f" fill="%s" font-family="Arial, sans-serif" font-size="12">%s</text>`,
columns[index], rowY, fill, html.EscapeString(text))
}
}
rowY += 30
lines := []string{}
duration := time.Duration((local.ExternalEgress.JD - local.ExternalIngress.JD) * 86400 * float64(time.Second)).Round(time.Second)
if language == "en" {
lines = append(lines, "Duration C1–C4 "+duration.String())
} else {
lines = append(lines, "一触至四触历时 "+duration.String())
}
for _, item := range []struct {
jd float64
zh, en string
}{{local.Sunrise, "凌日中日出 ", "Sunrise during transit "}, {local.Sunset, "凌日中日落 ", "Sunset during transit "}} {
if item.jd == 0 {
continue
}
label := item.zh
if language == "en" {
label = item.en
}
lines = append(lines, label+at(item.jd).Format("15:04:05"))
}
for _, line := range lines {
fmt.Fprintf(b, `<text x="%.3f" y="%.3f" fill="#333" font-family="Arial, sans-serif" font-size="12">%s</text>`, x, rowY, html.EscapeString(line))
rowY += 19
}
}
func transitLocalFooterLines(local basic.PlanetTransitLocalResult, options TransitLocalSVGOptions, width float64) []string {
note := options.FooterNote
if note == "" {
if options.Language == "en" {
note = "Sky view, north up and east left. Topocentric contacts; Sun altitudes are geometric centre altitudes, grey parts have the Sun's centre below the apparent horizon (standard refraction)."
} else {
note = "天空视向,上北左东;站心接触时刻,太阳高度为太阳中心几何高度,灰色部分太阳中心在视地平下(计入标准大气折射)。"
}
}
scaleNote := timenote.Scale(options.TimeScale, basic.JD2DateByZone(local.Greatest.JD, time.UTC, false), options.Location, options.Language)
return svgchart.FooterLinesWithScale(svgchart.WrapText(note, width-80, 12), scaleNote, width-80, 12, 3)
}
func transitLocalFooterBaselines(lineCount int, height float64) []float64 {
baselines, _ := svgchart.FooterBlock(lineCount, height, 12, svgchart.FooterLineHeight(12), svgchart.FooterBottomPadding(12)+18)
return baselines
}
func writeTransitLocalFooter(b *strings.Builder, lines []string, baselines []float64) {
for index, line := range lines {
fmt.Fprintf(b, `<text x="40" y="%.3f" fill="#555" font-family="Georgia, 'Times New Roman', serif" font-size="12">%s</text>`,
baselines[index], html.EscapeString(line))
}
}