astro/basic/saturn_ring_test.go

package basic

import (
	"fmt"
	"math"
	"testing"

	"b612.me/astro/internal/ephem"
)

func TestSaturnRingParametersMeeusExample(t *testing.T) {
	earthLatitude, sunLatitude, positionAngle, deltaU, majorAxis, minorAxis := SaturnRingParameters(2448972.50068)

	assertClose(t, "EarthLatitude", earthLatitude, 16.4415, 0.0001)
	assertClose(t, "SunLatitude", sunLatitude, 14.6782, 0.0001)
	assertClose(t, "PositionAngle", positionAngle, 6.7406, 0.0001)
	assertClose(t, "DeltaU", deltaU, 4.1991, 0.0001)
	assertClose(t, "MajorAxis", majorAxis, 35.8687, 0.0001)
	assertClose(t, "MinorAxis", minorAxis, 10.1521, 0.0001)
}

func TestSaturnRingNFullMatchesDefault(t *testing.T) {
	jd := 2448972.50068

	defaultEarthLatitude, defaultSunLatitude, defaultPositionAngle, defaultDeltaU, defaultMajorAxis, defaultMinorAxis := SaturnRingParameters(jd)
	truncatedEarthLatitude, truncatedSunLatitude, truncatedPositionAngle, truncatedDeltaU, truncatedMajorAxis, truncatedMinorAxis := SaturnRingParametersN(jd, -1)

	assertSameFloat(t, "EarthLatitude", defaultEarthLatitude, truncatedEarthLatitude)
	assertSameFloat(t, "SunLatitude", defaultSunLatitude, truncatedSunLatitude)
	assertSameFloat(t, "PositionAngle", defaultPositionAngle, truncatedPositionAngle)
	assertSameFloat(t, "DeltaU", defaultDeltaU, truncatedDeltaU)
	assertSameFloat(t, "MajorAxis", defaultMajorAxis, truncatedMajorAxis)
	assertSameFloat(t, "MinorAxis", defaultMinorAxis, truncatedMinorAxis)
	assertSameFloat(t, "SaturnRingB", SaturnRingB(jd), SaturnRingBN(jd, -1))
	assertSameFloat(t, "SaturnRingSunB", SaturnRingSunB(jd), SaturnRingSunBN(jd, -1))
	assertSameFloat(t, "SaturnRingPositionAngle", SaturnRingPositionAngle(jd), SaturnRingPositionAngleN(jd, -1))
	assertSameFloat(t, "SaturnRingDeltaU", SaturnRingDeltaU(jd), SaturnRingDeltaUN(jd, -1))
}

func TestSaturnRingParametersNWithInstanceForwardsN(t *testing.T) {
	previous := ephem.Active()
	t.Cleanup(func() { ephem.SetActive(previous) })
	jd := 2458850.5
	names := []string{"EarthLatitude", "SunLatitude", "PositionAngle", "DeltaU", "MajorAxis", "MinorAxis"}
	for _, model := range []ephem.Model{ephem.Legacy, ephem.Semianalytic} {
		ephem.SetActive(model)
		inst := ephem.NewModelInstance(model)
		for _, n := range []int{-1, 0} {
			expectedEarthLatitude, expectedSunLatitude, expectedPositionAngle, expectedDeltaU, expectedMajorAxis, expectedMinorAxis := SaturnRingParametersN(jd, n)
			gotEarthLatitude, gotSunLatitude, gotPositionAngle, gotDeltaU, gotMajorAxis, gotMinorAxis := SaturnRingParametersNWithInstance(jd, n, inst)
			got := []float64{gotEarthLatitude, gotSunLatitude, gotPositionAngle, gotDeltaU, gotMajorAxis, gotMinorAxis}
			expected := []float64{expectedEarthLatitude, expectedSunLatitude, expectedPositionAngle, expectedDeltaU, expectedMajorAxis, expectedMinorAxis}
			for index := range names {
				assertClose(t, fmt.Sprintf("model=%d n=%d %s", model, n, names[index]), got[index], expected[index], 1e-10)
			}
		}
	}
}

func TestSaturnRingParametersNWithInstanceIsolatedFromGlobalModel(t *testing.T) {
	previous := ephem.Active()
	t.Cleanup(func() { ephem.SetActive(previous) })
	jd := 2458850.5
	names := []string{"EarthLatitude", "SunLatitude", "PositionAngle", "DeltaU", "MajorAxis", "MinorAxis"}
	for _, testCase := range []struct {
		globalModel   ephem.Model
		instanceModel ephem.Model
	}{
		{globalModel: ephem.Legacy, instanceModel: ephem.Semianalytic},
		{globalModel: ephem.Semianalytic, instanceModel: ephem.Legacy},
	} {
		inst := ephem.NewModelInstance(testCase.instanceModel)
		for _, n := range []int{-1, 0} {
			ephem.SetActive(testCase.instanceModel)
			expectedEarthLatitude, expectedSunLatitude, expectedPositionAngle, expectedDeltaU, expectedMajorAxis, expectedMinorAxis := SaturnRingParametersN(jd, n)
			ephem.SetActive(testCase.globalModel)
			gotEarthLatitude, gotSunLatitude, gotPositionAngle, gotDeltaU, gotMajorAxis, gotMinorAxis := SaturnRingParametersNWithInstance(jd, n, inst)
			got := []float64{gotEarthLatitude, gotSunLatitude, gotPositionAngle, gotDeltaU, gotMajorAxis, gotMinorAxis}
			expected := []float64{expectedEarthLatitude, expectedSunLatitude, expectedPositionAngle, expectedDeltaU, expectedMajorAxis, expectedMinorAxis}
			for index := range names {
				assertClose(t, fmt.Sprintf("global=%d instance=%d n=%d %s", testCase.globalModel, testCase.instanceModel, n, names[index]), got[index], expected[index], 1e-10)
			}
		}
	}
}

func assertClose(t *testing.T, name string, got, want, tolerance float64) {
	t.Helper()
	if math.Abs(got-want) > tolerance {
		t.Fatalf("%s mismatch: got %.12f want %.12f tolerance %.12f", name, got, want, tolerance)
	}
}

func assertSameFloat(t *testing.T, name string, got, want float64) {
	t.Helper()
	if math.Float64bits(got) != math.Float64bits(want) {
		t.Fatalf("%s full-n mismatch: got %.18f want %.18f", name, got, want)
	}
}