b612
2bf8478639
- 新增日月食中心带、偏食带、阴影足迹、等时线、食分线及升落边界计算，支持极区与混合食拓扑 - 新增日食单时刻阴影求解器、站心状态查询、批量采样和 ΔT 覆盖接口 - 重构恒星与行星月掩路径，补充有限盘面接触、站心修正、掩带宽度、极区投影及升落边界 - 扩展 SVG 与 GeoJSON 输出，支持详细面板、全球/极区/地球投影、边界闭合、时间标记和拓扑签名 - 扩展日月食候选搜索、局地搜索、沙罗序列预计算与范围外推，补充系列锚点和成员一致性校验 - 补齐古历纪年、儒略历独有闰日、多公历候选、历法改革跨日及精确日期运算接口 - 优化 ΔT、章动、恒星时、月球地平线、事件根搜索和本地星历缓存，降低重复计算开销并提升边界稳定
106 lines
3.7 KiB
Go
106 lines
3.7 KiB
Go
package svg
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import (
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"fmt"
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"html"
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"math"
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"strings"
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"time"
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"b612.me/astro/moon"
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)
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// localOccultationMoonAppearance contains the apparent lunar illumination used
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// by the fixed-site occultation diagrams. The limb angle is topocentric so the
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// rendered bright side follows the same observer geometry as the occultation.
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type localOccultationMoonAppearance struct {
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illumination float64
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brightLimbPA float64
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}
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func localOccultationMoonAppearanceAt(date time.Time, observer moon.Observer) localOccultationMoonAppearance {
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illumination := moon.Phase(date)
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if !starOccultationFinite(illumination) {
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illumination = 1
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}
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illumination = math.Max(0, math.Min(1, illumination))
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brightLimbPA := moon.TopocentricBrightLimbPositionAngle(
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date, observer.Longitude, observer.Latitude, observer.Height,
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)
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if !starOccultationFinite(brightLimbPA) {
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brightLimbPA = 0
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}
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return localOccultationMoonAppearance{
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illumination: illumination,
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brightLimbPA: brightLimbPA,
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}
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}
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// writeLocalOccultationMoon draws a textured lunar disk with a phase-aware
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// terminator. clipID is unique within the SVG document because each stage
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// can have a different event time and therefore a different lunar phase.
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func writeLocalOccultationMoon(
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b *strings.Builder,
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cx, cy, radius float64,
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class string,
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appearance localOccultationMoonAppearance,
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clipID string,
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) {
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if !starOccultationFinite(radius) || radius <= 0 {
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return
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}
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illumination := math.Max(0, math.Min(1, appearance.illumination))
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brightLimbPA := appearance.brightLimbPA
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if !starOccultationFinite(brightLimbPA) {
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brightLimbPA = 0
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}
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fmt.Fprintf(b, `<g class="%s" data-illumination="%.6f" data-bright-limb-position-angle="%.3f">`,
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html.EscapeString(class), illumination, brightLimbPA)
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if illumination < 1-1e-6 {
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fmt.Fprintf(b, `<circle class="moon-phase-dark" cx="%.3f" cy="%.3f" r="%.3f" fill="#24272a"/>`, cx, cy, radius)
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}
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if illumination > 1e-6 {
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if illumination >= 1-1e-6 {
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writeLocalOccultationMoonTexture(b, cx, cy, radius)
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} else {
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path := localOccultationMoonPhasePath(radius, illumination)
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rotation := localOccultationMoonSVGRotation(brightLimbPA)
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fmt.Fprintf(b, `<clipPath id="%s"><path d="%s" transform="translate(%.3f %.3f) rotate(%.3f)"/></clipPath>`,
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html.EscapeString(clipID), path, cx, cy, rotation)
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fmt.Fprintf(b, `<g class="moon-phase-lit" clip-path="url(#%s)">`, html.EscapeString(clipID))
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writeLocalOccultationMoonTexture(b, cx, cy, radius)
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b.WriteString(`</g>`)
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}
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}
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fmt.Fprintf(b, `<circle cx="%.3f" cy="%.3f" r="%.3f" fill="none" stroke="#4f5d60" stroke-width="1.1" opacity="0.9"/>`, cx, cy, radius)
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b.WriteString(`</g>`)
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}
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func writeLocalOccultationMoonTexture(b *strings.Builder, cx, cy, radius float64) {
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fmt.Fprintf(b, `<use href="#le-moon" x="%.3f" y="%.3f" width="%.3f" height="%.3f"/>`,
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cx-radius, cy-radius, radius*2, radius*2)
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}
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// The chart uses north-up and east-left coordinates. SVG rotations are
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// clockwise from +X, so a celestial position angle of 0 points upward and 90
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// points left after this conversion.
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func localOccultationMoonSVGRotation(brightLimbPA float64) float64 {
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return -brightLimbPA - 90
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}
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// localOccultationMoonPhasePath returns the illuminated portion of a unit
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// projected lunar disk. The outer arc is the visible limb; the inner ellipse
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// is the projected terminator. The +X side is the bright side before rotation.
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func localOccultationMoonPhasePath(radius, illumination float64) string {
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cosPhase := 2*illumination - 1
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terminatorRadius := radius * math.Abs(cosPhase)
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sweep := 1
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if cosPhase < 0 {
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sweep = 0
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}
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return fmt.Sprintf(
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"M 0 %.3f A %.3f %.3f 0 0 1 0 %.3f A %.3f %.3f 0 0 %d 0 %.3f Z",
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-radius, radius, radius, radius, terminatorRadius, radius, sweep, -radius,
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)
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}
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