From 89a1b3a540abe0603b54e5c064e9f8931afd0d79 Mon Sep 17 00:00:00 2001 From: Meno Hochschild Date: Tue, 8 Sep 2020 21:49:19 +0200 Subject: [PATCH] determining time for given length of shadow --- .../net/time4j/calendar/astro/SolarTime.java | 175 ++++++++++++++++-- .../time4j/calendar/astro/SunPosition.java | 3 +- 2 files changed, 159 insertions(+), 19 deletions(-) diff --git a/time4j-android/src/main/java/net/time4j/calendar/astro/SolarTime.java b/time4j-android/src/main/java/net/time4j/calendar/astro/SolarTime.java index 7f71d72..55c1d75 100644 --- a/time4j-android/src/main/java/net/time4j/calendar/astro/SolarTime.java +++ b/time4j-android/src/main/java/net/time4j/calendar/astro/SolarTime.java @@ -25,6 +25,7 @@ import net.time4j.PlainDate; import net.time4j.PlainTime; import net.time4j.PlainTimestamp; +import net.time4j.base.MathUtils; import net.time4j.base.ResourceLoader; import net.time4j.engine.CalendarDate; import net.time4j.engine.ChronoCondition; @@ -205,6 +206,7 @@ public final class SolarTime static final double STD_ZENITH = 90.0 + (SUN_RADIUS + STD_REFRACTION) / 60.0; static final String DECLINATION = "declination"; static final String RIGHT_ASCENSION = "right-ascension"; + static final double ARC_MIN = 1.0 / 60; private static final Calculator DEFAULT_CALCULATOR; private static final ConcurrentMap CALCULATORS; @@ -936,6 +938,104 @@ public Moment apply(CalendarDate date) { } + /** + *

Calculates the moment before noon when the given shadow occurs on given date + * at the location of this instance.

+ * + *

The function is not supported in polar regions (+/- 66°) because the angle of sun + * is often changing too slowly to guarantee reliable results. Furthermore, the function + * might obtain a null result if the given shadow is too short for the date in question.

+ * + * @param objectHeight the height of object in meters, must be positive + * @param shadowLength the length of shadow thrown by the object in meters, must not be negative + * @return function for calculating the time of shadow applicable on any calendar date in minute precision + * @throws IllegalArgumentException if one or both parameters are not finite or out of range + * @throws UnsupportedOperationException if this instance is within the arctic or antarctic circle + * @see SunPosition#getShadowLength(double) + * @see #timeOfShadowAfterNoon(double, double) + * @since 4.7 + */ + /*[deutsch] + *

Berechnet den Moment in der ersten Tageshälfte, zu dem der fragliche Schatten beobachtet + * wird, an der Position dieser Instanz.

+ * + *

Die Funktion wird in Polargebieten (+/- 66°) nicht unterstützt, weil sich der Winkel der Sonne + * oft zu wenig verändert, um zuverlässige Ergebnisse zu ermöglichen. Außerdem kann + * die Funktion ohne Ergebnis sein, wenn der angegebene Schatten zum fraglichen Tag zu kurz ist.

+ * + * @param objectHeight the height of object in meters, must be positive + * @param shadowLength the length of shadow thrown by the object in meters, must not be negative + * @return function for calculating the time of shadow applicable on any calendar date in minute precision + * @throws IllegalArgumentException if one or both parameters are not finite or out of range + * @throws UnsupportedOperationException if this instance is within the arctic or antarctic circle + * @see SunPosition#getShadowLength(double) + * @see #timeOfShadowAfterNoon(double, double) + * @since 4.7 + */ + public ChronoFunction timeOfShadowBeforeNoon( + final double objectHeight, + final double shadowLength + ) { + + this.checkShadow(objectHeight, shadowLength); + return new ChronoFunction() { + @Override + public Moment apply(CalendarDate date) { + return SolarTime.this.timeOfShadow(date, false, objectHeight, shadowLength); + } + }; + + } + + /** + *

Calculates the moment after noon when the given shadow occurs on given date + * at the location of this instance.

+ * + *

The function is not supported in polar regions (+/- 66°) because the angle of sun + * is often changing too slowly to guarantee reliable results. Furthermore, the function + * might obtain a null result if the given shadow is too short for the date in question.

+ * + * @param objectHeight the height of object in meters, must be positive + * @param shadowLength the length of shadow thrown by the object in meters, must not be negative + * @return function for calculating the time of shadow applicable on any calendar date in minute precision + * @throws IllegalArgumentException if one or both parameters are not finite or out of range + * @throws UnsupportedOperationException if this instance is within the arctic or antarctic circle + * @see SunPosition#getShadowLength(double) + * @see #timeOfShadowBeforeNoon(double, double) + * @since 4.7 + */ + /*[deutsch] + *

Berechnet den Moment in der zweiten Tageshälfte, zu dem der fragliche Schatten beobachtet + * wird, an der Position dieser Instanz.

+ * + *

Die Funktion wird in Polargebieten (+/- 66°) nicht unterstützt, weil sich der Winkel der Sonne + * oft zu wenig verändert, um zuverlässige Ergebnisse zu ermöglichen. Außerdem kann + * die Funktion ohne Ergebnis sein, wenn der angegebene Schatten zum fraglichen Tag zu kurz ist.

+ * + * @param objectHeight the height of object in meters, must be positive + * @param shadowLength the length of shadow thrown by the object in meters, must not be negative + * @return function for calculating the time of shadow applicable on any calendar date in minute precision + * @throws IllegalArgumentException if one or both parameters are not finite or out of range + * @throws UnsupportedOperationException if this instance is within the arctic or antarctic circle + * @see SunPosition#getShadowLength(double) + * @see #timeOfShadowBeforeNoon(double, double) + * @since 4.7 + */ + public ChronoFunction timeOfShadowAfterNoon( + final double objectHeight, + final double shadowLength + ) { + + this.checkShadow(objectHeight, shadowLength); + return new ChronoFunction() { + @Override + public Moment apply(CalendarDate date) { + return SolarTime.this.timeOfShadow(date, true, objectHeight, shadowLength); + } + }; + + } + @Override public boolean equals(Object obj) { @@ -1235,14 +1335,12 @@ static Moment fromLocalEvent( } private static PlainTimestamp onAverage(Moment context, ZonalOffset offset) { - Moment ut = Moment.of( context.getElapsedTime(TimeScale.UT) + 2 * 365 * 86400, context.getNanosecond(TimeScale.UT), TimeScale.POSIX); return ut.toZonalTimestamp(offset); - } private static Moment transitAtNoon( @@ -1250,10 +1348,8 @@ private static Moment transitAtNoon( double longitude, String calculator ) { - Moment utc = fromLocalEvent(date, 12, longitude, calculator); return utc.with(Moment.PRECISION, precision(calculator)); - } private static Moment transitAtMidnight( @@ -1261,28 +1357,78 @@ private static Moment transitAtMidnight( double longitude, String calculator ) { - Moment utc = fromLocalEvent(date, 0, longitude, calculator); return utc.with(Moment.PRECISION, precision(calculator)); + } + private void checkShadow( + double objectHeight, + double shadowLength + ) { + if (Double.isInfinite(objectHeight) || Double.isNaN(objectHeight) || (objectHeight <= 0.0)) { + throw new IllegalArgumentException("Object height must be finite and positive."); + } else if (Double.isInfinite(shadowLength) || Double.isNaN(shadowLength) || (shadowLength < 0.0)) { + throw new IllegalArgumentException("Length of shadow must be finite and not negative."); + } else if (Math.abs(this.latitude) > 66.0) { + throw new UnsupportedOperationException("Cannot calculate time of shadow for polar regions."); + } } - private static TimeUnit precision(String calculator) { + private Moment timeOfShadow( + CalendarDate date, + boolean afterNoon, + double objectHeight, + double shadowLength + ) { + PlainDate d = toGregorian(toLMT(date)); + Moment riseset = afterNoon ? d.get(sunset()) : d.get(sunrise()); + assert riseset != null; + Moment noon = d.get(transitAtNoon()); + double maxE = SunPosition.at(noon, this).getElevation(); + + if (maxE <= ARC_MIN) { + return riseset; + } else { + double elevation = ( + (shadowLength == 0.0) + ? 90.0 + : Math.toDegrees(Math.atan(objectHeight / shadowLength))); - return (calculator.equals(StdSolarCalculator.SIMPLE.name()) ? TimeUnit.MINUTES : TimeUnit.SECONDS); + if (elevation > maxE + ARC_MIN) { + return null; + } else { + return timeOfShadow(riseset.getPosixTime(), noon.getPosixTime(), elevation); + } + } + } + + private Moment timeOfShadow( + long lowSun, + long highSun, + double elevation + ) { + Moment center = Moment.of(MathUtils.safeAdd(lowSun, highSun) / 2, TimeScale.POSIX); + double sunpos = SunPosition.at(center, this).getElevation(); + + if (Math.abs(sunpos - elevation) < ARC_MIN) { + return center; + } else if (Double.compare(elevation, sunpos) > 0.0) { + return timeOfShadow(center.getPosixTime(), highSun, elevation); + } else { + return timeOfShadow(lowSun, center.getPosixTime(), elevation); + } + } + private static TimeUnit precision(String calculator) { + return (calculator.equals(StdSolarCalculator.SIMPLE.name()) ? TimeUnit.MINUTES : TimeUnit.SECONDS); } private double geodeticAngle() { - return this.getCalculator().getGeodeticAngle(this.latitude, this.altitude); - } private double zenithAngle() { - return this.getCalculator().getZenithAngle(this.latitude, this.altitude); - } private static void check( @@ -1291,7 +1437,6 @@ private static void check( int altitude, String calculator ) { - if (Double.isNaN(latitude) || Double.isInfinite(latitude)) { throw new IllegalArgumentException("Latitude must be a finite value: " + latitude); } else if (Double.isNaN(longitude) || Double.isInfinite(longitude)) { @@ -1309,11 +1454,9 @@ private static void check( } else if (!CALCULATORS.containsKey(calculator)) { throw new IllegalArgumentException("Unknown calculator: " + calculator); } - } private CalendarDate toLMT(CalendarDate input) { - if ((this.observerZoneID == null) || (Math.abs(this.longitude) < 150.0)) { return input; } @@ -1328,14 +1471,12 @@ private CalendarDate toLMT(CalendarDate input) { ZonalOffset lmtOffset = ZonalOffset.atLongitude(new BigDecimal(this.longitude)); return noon.inTimezone(this.observerZoneID).toZonalTimestamp(lmtOffset).getCalendarDate(); - } private static boolean equalZones( TZID z1, TZID z2 ) { - if (z1 == null) { return (z2 == null); } else if (z2 == null) { @@ -1343,7 +1484,6 @@ private static boolean equalZones( } else { return z1.canonical().equals(z2.canonical()); } - } /** @@ -1358,7 +1498,6 @@ private void readObject(ObjectInputStream in) in.defaultReadObject(); check(this.latitude, this.longitude, this.altitude, this.calculator); - } //~ Innere Klassen ---------------------------------------------------- diff --git a/time4j-android/src/main/java/net/time4j/calendar/astro/SunPosition.java b/time4j-android/src/main/java/net/time4j/calendar/astro/SunPosition.java index 953d15c..120f91a 100644 --- a/time4j-android/src/main/java/net/time4j/calendar/astro/SunPosition.java +++ b/time4j-android/src/main/java/net/time4j/calendar/astro/SunPosition.java @@ -284,7 +284,8 @@ public double getShadowLength(double objectHeight) { } else if (e == 90.0) { return 0.0; } else { - return objectHeight / Math.tan(Math.toRadians(e)); + double len = objectHeight / Math.tan(Math.toRadians(e)); + return (len < SolarTime.ARC_MIN) ? 0.0 : len; } } else { throw new IllegalArgumentException("Object height must be finite and positive: " + objectHeight);