71 lines
3.0 KiB
Go
71 lines
3.0 KiB
Go
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package svg
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import (
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"testing"
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"time"
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"b612.me/astro/basic"
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eclipsecore "b612.me/astro/eclipse"
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"b612.me/astro/internal/svgmap"
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)
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// TestLunarEclipseMapSVGPolarWitnessStaysOutsideEquirectangularVisibility 固定全球月食地图在
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// 极区的可见性契约。等距圆柱投影在高纬把经度拉伸：1° 的球面地平弧在极点附近可以横跨近
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// 180° 经度，只连端点就会把地平线以外画进可见区。1904-09-24 的 P1 在南极点附近有一个
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// 月心高度约 −0.05° 的见证点，曾经被画进 visible-at-p1 多边形。
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// TestLunarEclipseMapSVGPolarWitnessStaysOutsideEquirectangularVisibility pins the polar
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// visibility contract of the global lunar-eclipse map. Equirectangular projection stretches
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// longitude near a pole: a 1-degree spherical horizon arc can span almost 180 degrees there, so
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// joining endpoints alone paints sky below the horizon as visible. At P1 of 1904-09-24 a witness
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// near the south pole sits about 0.05 degrees below the Moon's horizon and used to be painted
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// inside the visible-at-p1 polygon.
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func TestLunarEclipseMapSVGPolarWitnessStaysOutsideEquirectangularVisibility(t *testing.T) {
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date := time.Date(1904, 9, 24, 0, 0, 0, 0, time.UTC)
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info, ok := eclipsecore.LunarEclipseOnDate(date)
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if !ok {
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t.Fatal("missing lunar eclipse")
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}
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frame := eclipseMapFrame(lunarEclipseMapDefaultWidth, lunarEclipseMapDefaultHeight,
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svgmap.ProjectionEquirectangular, 142, 92)
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path, boundary := lunarEclipseVisibilityPath(info.PenumbralStart, frame)
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if len(boundary) == 0 {
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t.Fatal("visibility path has no boundary")
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}
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rings := svgClosedPathRings(t, `<path d="`+path+`"/>`)
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if len(rings) == 0 {
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t.Fatal("visibility path has no rings")
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}
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jd := basic.Date2JDE(info.PenumbralStart)
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// 只取足够深入地平线以下的见证点：−89.9° 处月心高度约 −0.054°，而更靠近极点的
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// −89.99° 只有约 −0.004°，落在可见性判定本身的数值容差里，不能作为回归依据。
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// Only a witness clearly below the horizon is used: at -89.9 degrees the Moon centre sits
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// about 0.054 degrees down, while -89.99 degrees is only about 0.004 degrees down and lies
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// inside the numerical tolerance of the visibility test itself.
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witnesses := []struct {
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longitude float64
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latitude float64
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}{
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{-115, -89.9},
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}
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for _, witness := range witnesses {
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altitude := basic.HMoonHeight(jd, witness.longitude, witness.latitude, 0)
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if altitude >= -0.01 {
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// 见证点必须先确实是地平线以下，否则这个回归就失去意义。
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t.Fatalf("witness (%g,%g) altitude=%g, want below the horizon",
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witness.longitude, witness.latitude, altitude)
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}
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x, y, projectable := frame.Project(witness.longitude, witness.latitude)
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if !projectable {
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continue
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}
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inside := false
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for _, ring := range rings {
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inside = inside || pointInLunarVisibilityPolygon(x, y, ring)
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}
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if inside {
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t.Fatalf("below-horizon witness (%g,%g) altitude=%g is painted inside the visible region",
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witness.longitude, witness.latitude, altitude)
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}
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}
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}
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