BurstSelector.java
/* Copyright 2002-2019 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.time;
import java.util.ArrayList;
import java.util.List;
import org.hipparchus.util.FastMath;
/** Selector generating high rate bursts of dates separated by some rest period.
* <p>
* The dates can be aligned to whole steps in some time scale. So for example
* if a rest period of 3600s is used and the alignment time scale is set to
* {@link org.orekit.time.TimeScalesFactory#getUTC() UTC}, the earliest date of
* each burst will occur at whole hours in UTC time.
* </p>
* <p>
* BEWARE! This class stores internally the last selected dates, so it is <em>neither</em>
* reusable across several {@link org.orekit.estimation.measurements.generation.EventBasedScheduler
* fixed step} or {@link org.orekit.estimation.measurements.generation.ContinuousScheduler
* continuous} schedulers, <em>nor</em> thread-safe. A separate selector should be used for each
* scheduler and for each thread in multi-threading context.
* </p>
* @author Luc Maisonobe
* @since 9.3
*/
public class BurstSelector implements DatesSelector {
/** Maximum number of selected dates in a burst. */
private final int maxBurstSize;
/** Step between two consecutive dates within a burst. */
private final double highRateStep;
/** Period between the start of each burst. */
private final double burstPeriod;
/** Alignment time scale (null is alignment is not needed). */
private final TimeScale alignmentTimeScale;
/** First date in last burst. */
private AbsoluteDate first;
/** Last selected date. */
private AbsoluteDate last;
/** Index of last selected date in current burst. */
private int index;
/** Simple constructor.
* <p>
* The {@code burstPeriod} ignores the duration of the burst itself. This
* means that if burst of {@code maxBurstSize=256} dates each separated by
* {@code highRateStep=100ms} should be selected with {@code burstPeriod=300s},
* then the first burst would contain 256 dates from {@code t0} to {@code t0+25.5s}
* and the second burst would start at {@code t0+300s}, <em>not</em> at
* {@code t0+325.5s}.
* </p>
* <p>
* If alignment to some time scale is needed, it applies only to the first date in
* each burst.
* </p>
* @param maxBurstSize maximum number of selected dates in a burst
* @param highRateStep step between two consecutive dates within a burst (s)
* @param burstPeriod period between the start of each burst (s)
* @param alignmentTimeScale alignment time scale for first date in burst
* (null is alignment is not needed)
*/
public BurstSelector(final int maxBurstSize, final double highRateStep,
final double burstPeriod, final TimeScale alignmentTimeScale) {
this.maxBurstSize = maxBurstSize;
this.highRateStep = highRateStep;
this.burstPeriod = burstPeriod;
this.alignmentTimeScale = alignmentTimeScale;
this.last = null;
this.first = null;
this.index = 0;
}
/** {@inheritDoc} */
@Override
public List<AbsoluteDate> selectDates(final AbsoluteDate start, final AbsoluteDate end) {
final int increment = end.durationFrom(start) > 0 ? +1 : -1;
final int firstIndex = increment > 0 ? 0 : maxBurstSize - 1;
final int lastIndex = maxBurstSize - 1 - firstIndex;
final double signedHighRateStep = FastMath.copySign(highRateStep, increment);
final double signedBurstPeriod = FastMath.copySign(burstPeriod, increment);
final List<AbsoluteDate> selected = new ArrayList<>();
final boolean reset = first == null || increment * start.durationFrom(first) > burstPeriod;
if (reset) {
first = null;
index = firstIndex;
}
for (AbsoluteDate next = reset ? start : last.shiftedBy(signedHighRateStep);
increment * next.durationFrom(end) <= 0;
next = last.shiftedBy(signedHighRateStep)) {
if (index == lastIndex + increment) {
// we have exceeded burst size, jump to next burst
next = first.shiftedBy(signedBurstPeriod);
first = null;
index = firstIndex;
if (increment * next.durationFrom(end) > 0) {
// next burst is out of current interval
break;
}
}
if (first == null && alignmentTimeScale != null) {
// align earliest burst date to time scale
final double offset = firstIndex * highRateStep;
final double t = next.getComponents(alignmentTimeScale).getTime().getSecondsInLocalDay() - offset;
final double dt = burstPeriod * FastMath.round(t / burstPeriod) - t;
next = next.shiftedBy(dt);
while (index != lastIndex && increment * next.durationFrom(start) < 0) {
next = next.shiftedBy(signedHighRateStep);
index += increment;
}
if (increment * next.durationFrom(start) < 0) {
// alignment shifted date out of interval
next = next.shiftedBy(signedBurstPeriod - (maxBurstSize - 1) * signedHighRateStep);
index = firstIndex;
}
}
if (increment * next.durationFrom(start) >= 0) {
if (increment * next.durationFrom(end) <= 0) {
// the date is within range, select it
if (first == null) {
first = next.shiftedBy(-signedHighRateStep * index);
}
selected.add(next);
} else {
// we have exceeded date range
break;
}
}
last = next;
index += increment;
}
return selected;
}
}