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Converted the PassPredictor class to Kotlin. Removed the class reference to Apache Commons Logging library which was causing an error during the code minification.
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/**
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* predict4java: An SDP4 / SGP4 library for satellite orbit predictions
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*
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* Copyright (C) 2004-2010 David A. B. Johnson, G4DPZ.
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*
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* This class is a Java port of one of the core elements of
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* the Predict program, Copyright John A. Magliacane,
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* KD2BD 1991-2003: http://www.qsl.net/kd2bd/predict.html
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*
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* Dr. T.S. Kelso is the author of the SGP4/SDP4 orbital models,
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* originally written in Fortran and Pascal, and released into the
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* public domain through his website (http://www.celestrak.com/).
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* Neoklis Kyriazis, 5B4AZ, later re-wrote Dr. Kelso's code in C,
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* and released it under the GNU GPL in 2002.
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* PREDICT's core is based on 5B4AZ's code translation efforts.
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*
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* Author: David A. B. Johnson, G4DPZ <dave></dave>@g4dpz.me.uk>
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*
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* Comments, questions and bugreports should be submitted via
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* http://sourceforge.net/projects/websat/
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* More details can be found at the project home page:
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*
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* http://websat.sourceforge.net
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, visit http://www.fsf.org/
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*/
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package com.rtbishop.look4sat.predict4kotlin
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import com.github.amsacode.predict4java.*
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import java.util.*
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class PassPredictor(private val tle: TLE, private val qth: GroundStationPosition) {
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private val sat: Satellite = SatelliteFactory.createSatellite(tle)
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private val south = "south"
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private val north = "north"
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private val deadSpotNone = "none"
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private val speedOfLight = 2.99792458E8
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private val twoPi = Math.PI * 2.0
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private val timeZone: TimeZone = TimeZone.getTimeZone("UTC")
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private var iterationCount = 0
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fun getDownlinkFreq(freq: Long, date: Date): Long {
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val cal = Calendar.getInstance(timeZone).apply {
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clear()
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timeInMillis = date.time
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}
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val satPos = getSatPos(cal.time)
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val rangeRate = satPos.rangeRate
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return (freq.toDouble() * (speedOfLight - rangeRate * 1000.0) / speedOfLight).toLong()
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}
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fun getUplinkFreq(freq: Long, date: Date): Long {
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val cal = Calendar.getInstance(timeZone).apply {
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clear()
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timeInMillis = date.time
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}
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val satPos = getSatPos(cal.time)
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val rangeRate = satPos.rangeRate
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return (freq.toDouble() * (speedOfLight + rangeRate * 1000.0) / speedOfLight).toLong()
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}
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fun getSatPos(time: Date): SatPos {
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iterationCount++
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return sat.getPosition(qth, time)
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}
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fun getPositions(
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referenceDate: Date,
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incrementSeconds: Int,
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minutesBefore: Int,
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minutesAfter: Int
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): List<SatPos> {
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val positions: MutableList<SatPos> = ArrayList()
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val endDateDate = Date(referenceDate.time + minutesAfter * 60L * 1000L)
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var trackDate = Date(referenceDate.time - minutesBefore * 60L * 1000L)
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while (trackDate.before(endDateDate)) {
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positions.add(getSatPos(trackDate))
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trackDate = Date(trackDate.time + incrementSeconds * 1000)
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}
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return positions
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}
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fun getPasses(start: Date, hoursAhead: Int, windBack: Boolean): List<SatPassTime> {
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iterationCount = 0
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val passes: MutableList<SatPassTime> = ArrayList()
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val trackEndDate = Date(start.time + hoursAhead * 60L * 60L * 1000L)
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var trackStartDate = start
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var windBackTime = windBack
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var lastAOS: Date
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var count = 0
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do {
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if (count > 0) windBackTime = false
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val pass = nextSatPass(trackStartDate, windBackTime)
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lastAOS = pass.startTime
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passes.add(pass)
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trackStartDate = Date(pass.endTime.time + threeQuarterOrbitMinutes() * 60L * 1000L)
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count++
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} while (lastAOS < trackEndDate)
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return passes
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}
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private fun nextSatPass(date: Date, windBack: Boolean = false): SatPassTime {
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val aosAzimuth: Int
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val losAzimuth: Int
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var maxElevation = 0.0
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var elevation: Double
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var prevPos: SatPos
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var tca: Date? = null
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var polePassed = deadSpotNone
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// get the current position
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val cal = Calendar.getInstance(timeZone).apply {
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clear()
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timeInMillis = date.time
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}
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// wind back time 1/4 of an orbit
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if (windBack) {
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val meanMotion = tle.meanmo
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cal.add(Calendar.MINUTE, (-24.0 * 60.0 / meanMotion / 4.0).toInt())
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}
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var satPos = getSatPos(cal.time)
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// test for the elevation being above the horizon
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if (satPos.elevation > 0.0) {
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// move time forward in 30 second intervals until the sat goes below the horizon
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do {
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satPos = getPosition(cal, 60)
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} while (satPos.elevation > 0.0)
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// move time forward 3/4 orbit
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cal.add(Calendar.MINUTE, threeQuarterOrbitMinutes())
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}
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// now find the next time it comes above the horizon
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do {
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satPos = getPosition(cal, 60)
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val now = cal.time
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elevation = satPos.elevation
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if (elevation > maxElevation) {
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maxElevation = elevation
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tca = now
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}
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} while (satPos.elevation < 0.0)
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// refine it to 5 seconds
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cal.add(Calendar.SECOND, -60)
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do {
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satPos = getPosition(cal, 5)
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val now = cal.time
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elevation = satPos.elevation
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if (elevation > maxElevation) {
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maxElevation = elevation
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tca = now
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}
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prevPos = satPos
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} while (satPos.elevation < 0.0)
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val startDate = satPos.time
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aosAzimuth = (satPos.azimuth / (2.0 * Math.PI) * 360.0).toInt()
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// now find when it goes below
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do {
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satPos = getPosition(cal, 30)
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val now = cal.time
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val currPolePassed = getPolePassed(prevPos, satPos)
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if (currPolePassed != deadSpotNone) {
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polePassed = currPolePassed
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}
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elevation = satPos.elevation
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if (elevation > maxElevation) {
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maxElevation = elevation
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tca = now
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}
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prevPos = satPos
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} while (satPos.elevation > 0.0)
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// refine it to 5 seconds
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cal.add(Calendar.SECOND, -30)
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do {
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satPos = getPosition(cal, 5)
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val now = cal.time
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elevation = satPos.elevation
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if (elevation > maxElevation) {
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maxElevation = elevation
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tca = now
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}
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} while (satPos.elevation > 0.0)
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val endDate = satPos.time
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losAzimuth = (satPos.azimuth / (2.0 * Math.PI) * 360.0).toInt()
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return SatPassTime(
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startDate, endDate, tca, polePassed, aosAzimuth,
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losAzimuth, maxElevation / (2.0 * Math.PI) * 360.0
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)
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}
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private fun getPosition(cal: Calendar, offSet: Int): SatPos {
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cal.add(Calendar.SECOND, offSet)
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return getSatPos(cal.time)
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}
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private fun getPolePassed(prevPos: SatPos, satPos: SatPos): String {
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var polePassed = deadSpotNone
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val az1 = prevPos.azimuth / twoPi * 360.0
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val az2 = satPos.azimuth / twoPi * 360.0
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if (az1 > az2) { // we may be moving from 350 or greater through north
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if (az1 > 350 && az2 < 10) polePassed = north
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else { // we may be moving from 190 or greater through south
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if (az1 > 180 && az2 < 180) polePassed = south
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}
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} else { // we may be moving from 10 or less through north
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if (az1 < 10 && az2 > 350) polePassed = north
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else { // we may be moving from 170 or more through south
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if (az1 < 180 && az2 > 180) polePassed = south
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}
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}
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return polePassed
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}
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private fun threeQuarterOrbitMinutes(): Int {
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return (24.0 * 60.0 / tle.meanmo * 0.75).toInt()
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}
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}
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