97 lines
3.1 KiB
Go
97 lines
3.1 KiB
Go
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package basic
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import "math"
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const (
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orbitReferenceJD = 2451545.0
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gaussianGravitationalConstant = 0.01720209895 // rad/day
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lightTimeDaysPerAU = 0.0057755183
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orbitParabolicTolerance = 1e-12
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)
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// OrbitElements 日心二体圆锥曲线根数，参考系为 J2000 平黄道/平春分点。
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// EpochJD 与 TpJD 使用 TT/TDB 对应的儒略日。
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//
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// 两种输入形式：
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// 1. 椭圆经典根数：A/E/I/Omega/W/M0（原有形式）
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// 2. 近日点形式：Q/E/I/Omega/W/TpJD，用于高偏心、抛物或双曲轨道
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//
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// 线性 rates 仅作用于经典根数形式，单位均为“每天变化量”。
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type OrbitElements struct {
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EpochJD float64
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A float64 // 半长径 / semi-major axis in AU.
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E float64 // 离心率 / eccentricity.
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I float64 // 轨道倾角 / inclination in degrees.
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Omega float64 // 升交点黄经 / longitude of ascending node in degrees.
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W float64 // 近日点幅角 / argument of perihelion in degrees.
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M0 float64 // 历元平近点角 / mean anomaly at epoch in degrees.
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Q float64 // 近日点距离 / perihelion distance in AU.
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TpJD float64 // 近日点通过时刻 / perihelion passage TT/TDB Julian day.
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ADot float64 // 半长径日变化 / daily rate of A in AU/day.
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EDot float64 // 离心率日变化 / daily rate of E per day.
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IDot float64 // 倾角日变化 / daily rate of I in deg/day.
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OmegaDot float64 // 升交点黄经日变化 / daily rate of Omega in deg/day.
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WDot float64 // 近日点幅角日变化 / daily rate of W in deg/day.
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MDot float64 // 平近点角日变化 / daily rate of M in deg/day.
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}
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func (elements OrbitElements) usesPerihelionForm() bool {
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return isFinitePositive(elements.Q) && isFinite(elements.TpJD)
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}
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func (elements OrbitElements) validOrientation() bool {
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angles := [...]float64{elements.I, elements.Omega, elements.W}
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for _, angle := range angles {
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if !isFinite(angle) {
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return false
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}
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}
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return true
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}
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func (elements OrbitElements) validEllipticClassical() bool {
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if !isFinite(elements.EpochJD) || !isFinitePositive(elements.A) {
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return false
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}
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if !isFinite(elements.E) || elements.E < 0 || elements.E >= 1 {
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return false
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}
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if !isFinite(elements.M0) {
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return false
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}
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return elements.validOrientation()
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}
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func (elements OrbitElements) validPerihelionForm() bool {
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if !elements.usesPerihelionForm() {
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return false
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}
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if !isFinite(elements.E) || elements.E < 0 {
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return false
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}
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return elements.validOrientation()
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}
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func orbitElementsAt(jd float64, elements OrbitElements) OrbitElements {
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if elements.usesPerihelionForm() || !isFinite(jd) || !isFinite(elements.EpochJD) {
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return elements
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}
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deltaDays := jd - elements.EpochJD
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updated := elements
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updated.A += updated.ADot * deltaDays
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updated.E += updated.EDot * deltaDays
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updated.I += updated.IDot * deltaDays
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updated.Omega += updated.OmegaDot * deltaDays
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updated.W += updated.WDot * deltaDays
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return updated
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}
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func isFinite(value float64) bool {
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return !(math.IsNaN(value) || math.IsInf(value, 0))
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}
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func isFinitePositive(value float64) bool {
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return isFinite(value) && value > 0
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}
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