FixedStepSelector.java
/* Copyright 2002-2022 CS GROUP
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* 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,
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package org.orekit.time;
import java.util.ArrayList;
import java.util.List;
import org.hipparchus.util.FastMath;
/** Selector generating a continuous stream of dates separated by a constant step.
* <p>
* The dates can be aligned to whole steps in some time scale. So for example
* if a step of 60s is used and the alignment time scale is set to
* {@link org.orekit.time.TimeScales#getUTC() UTC}, dates will be selected
* at whole minutes 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 FixedStepSelector implements DatesSelector {
/** Step between two consecutive dates. */
private final double step;
/** Alignment time scale (null is alignment is not needed). */
private final TimeScale alignmentTimeScale;
/** Last selected date. */
private AbsoluteDate last;
/** Simple constructor.
* @param step step between two consecutive dates (s)
* @param alignmentTimeScale alignment time scale (null is alignment is not needed)
*/
public FixedStepSelector(final double step, final TimeScale alignmentTimeScale) {
this.step = step;
this.alignmentTimeScale = alignmentTimeScale;
this.last = null;
}
/** {@inheritDoc} */
@Override
public List<AbsoluteDate> selectDates(final AbsoluteDate start, final AbsoluteDate end) {
final double sign = FastMath.copySign(1, end.durationFrom(start));
final List<AbsoluteDate> selected = new ArrayList<>();
final boolean reset = last == null || sign * start.durationFrom(last) > step;
for (AbsoluteDate next = reset ? start : last.shiftedBy(sign * step);
sign * next.durationFrom(end) <= 0;
next = last.shiftedBy(sign * step)) {
if (alignmentTimeScale != null) {
// align date to time scale
final double t = next.getComponents(alignmentTimeScale).getTime().getSecondsInLocalDay();
final double dt = step * FastMath.round(t / step) - t;
next = next.shiftedBy(dt);
}
if (sign * next.durationFrom(start) >= 0) {
if (sign * next.durationFrom(end) <= 0) {
// the date is within range, select it
selected.add(next);
} else {
// we have exceeded date range
break;
}
}
last = next;
}
return selected;
}
}