Converted the PassPredictor class to Kotlin. Removed the class reference to Apache Commons Logging library which was causing an error during the code minification.

app/src/main/java/com/rtbishop/look4sat/predict4kotlin/PassPredictor.kt

@@ -0,0 +1,239 @@
+/**
+ * predict4java: An SDP4 / SGP4 library for satellite orbit predictions
+ *
+ * Copyright (C)  2004-2010  David A. B. Johnson, G4DPZ.
+ *
+ * This class is a Java port of one of the core elements of
+ * the Predict program, Copyright John A. Magliacane,
+ * KD2BD 1991-2003: http://www.qsl.net/kd2bd/predict.html
+ *
+ * Dr. T.S. Kelso is the author of the SGP4/SDP4 orbital models,
+ * originally written in Fortran and Pascal, and released into the
+ * public domain through his website (http://www.celestrak.com/).
+ * Neoklis Kyriazis, 5B4AZ, later re-wrote Dr. Kelso's code in C,
+ * and released it under the GNU GPL in 2002.
+ * PREDICT's core is based on 5B4AZ's code translation efforts.
+ *
+ * Author: David A. B. Johnson, G4DPZ <dave></dave>@g4dpz.me.uk>
+ *
+ * Comments, questions and bugreports should be submitted via
+ * http://sourceforge.net/projects/websat/
+ * More details can be found at the project home page:
+ *
+ * http://websat.sourceforge.net
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, visit http://www.fsf.org/
+ */
+package com.rtbishop.look4sat.predict4kotlin
+
+import com.github.amsacode.predict4java.*
+import java.util.*
+
+class PassPredictor(private val tle: TLE, private val qth: GroundStationPosition) {
+    private val sat: Satellite = SatelliteFactory.createSatellite(tle)
+    private val south = "south"
+    private val north = "north"
+    private val deadSpotNone = "none"
+    private val speedOfLight = 2.99792458E8
+    private val twoPi = Math.PI * 2.0
+    private val timeZone: TimeZone = TimeZone.getTimeZone("UTC")
+    private var iterationCount = 0
+
+    fun getDownlinkFreq(freq: Long, date: Date): Long {
+        val cal = Calendar.getInstance(timeZone).apply {
+            clear()
+            timeInMillis = date.time
+        }
+        val satPos = getSatPos(cal.time)
+        val rangeRate = satPos.rangeRate
+        return (freq.toDouble() * (speedOfLight - rangeRate * 1000.0) / speedOfLight).toLong()
+    }
+
+    fun getUplinkFreq(freq: Long, date: Date): Long {
+        val cal = Calendar.getInstance(timeZone).apply {
+            clear()
+            timeInMillis = date.time
+        }
+        val satPos = getSatPos(cal.time)
+        val rangeRate = satPos.rangeRate
+        return (freq.toDouble() * (speedOfLight + rangeRate * 1000.0) / speedOfLight).toLong()
+    }
+
+    fun getSatPos(time: Date): SatPos {
+        iterationCount++
+        return sat.getPosition(qth, time)
+    }
+
+    fun getPositions(
+        referenceDate: Date,
+        incrementSeconds: Int,
+        minutesBefore: Int,
+        minutesAfter: Int
+    ): List<SatPos> {
+        val positions: MutableList<SatPos> = ArrayList()
+        val endDateDate = Date(referenceDate.time + minutesAfter * 60L * 1000L)
+        var trackDate = Date(referenceDate.time - minutesBefore * 60L * 1000L)
+
+        while (trackDate.before(endDateDate)) {
+            positions.add(getSatPos(trackDate))
+            trackDate = Date(trackDate.time + incrementSeconds * 1000)
+        }
+
+        return positions
+    }
+
+    fun getPasses(start: Date, hoursAhead: Int, windBack: Boolean): List<SatPassTime> {
+        iterationCount = 0
+
+        val passes: MutableList<SatPassTime> = ArrayList()
+        val trackEndDate = Date(start.time + hoursAhead * 60L * 60L * 1000L)
+        var trackStartDate = start
+        var windBackTime = windBack
+        var lastAOS: Date
+        var count = 0
+
+        do {
+            if (count > 0) windBackTime = false
+            val pass = nextSatPass(trackStartDate, windBackTime)
+            lastAOS = pass.startTime
+            passes.add(pass)
+            trackStartDate = Date(pass.endTime.time + threeQuarterOrbitMinutes() * 60L * 1000L)
+            count++
+        } while (lastAOS < trackEndDate)
+
+        return passes
+    }
+
+    private fun nextSatPass(date: Date, windBack: Boolean = false): SatPassTime {
+        val aosAzimuth: Int
+        val losAzimuth: Int
+        var maxElevation = 0.0
+        var elevation: Double
+        var prevPos: SatPos
+        var tca: Date? = null
+        var polePassed = deadSpotNone
+
+        // get the current position
+        val cal = Calendar.getInstance(timeZone).apply {
+            clear()
+            timeInMillis = date.time
+        }
+
+        // wind back time 1/4 of an orbit
+        if (windBack) {
+            val meanMotion = tle.meanmo
+            cal.add(Calendar.MINUTE, (-24.0 * 60.0 / meanMotion / 4.0).toInt())
+        }
+        var satPos = getSatPos(cal.time)
+
+        // test for the elevation being above the horizon
+        if (satPos.elevation > 0.0) {
+            // move time forward in 30 second intervals until the sat goes below the horizon
+            do {
+                satPos = getPosition(cal, 60)
+            } while (satPos.elevation > 0.0)
+            // move time forward 3/4 orbit
+            cal.add(Calendar.MINUTE, threeQuarterOrbitMinutes())
+        }
+
+        // now find the next time it comes above the horizon
+        do {
+            satPos = getPosition(cal, 60)
+            val now = cal.time
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                tca = now
+            }
+        } while (satPos.elevation < 0.0)
+
+        // refine it to 5 seconds
+        cal.add(Calendar.SECOND, -60)
+        do {
+            satPos = getPosition(cal, 5)
+            val now = cal.time
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                tca = now
+            }
+            prevPos = satPos
+        } while (satPos.elevation < 0.0)
+        val startDate = satPos.time
+        aosAzimuth = (satPos.azimuth / (2.0 * Math.PI) * 360.0).toInt()
+
+        // now find when it goes below
+        do {
+            satPos = getPosition(cal, 30)
+            val now = cal.time
+            val currPolePassed = getPolePassed(prevPos, satPos)
+            if (currPolePassed != deadSpotNone) {
+                polePassed = currPolePassed
+            }
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                tca = now
+            }
+            prevPos = satPos
+        } while (satPos.elevation > 0.0)
+
+        // refine it to 5 seconds
+        cal.add(Calendar.SECOND, -30)
+        do {
+            satPos = getPosition(cal, 5)
+            val now = cal.time
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                tca = now
+            }
+        } while (satPos.elevation > 0.0)
+
+        val endDate = satPos.time
+        losAzimuth = (satPos.azimuth / (2.0 * Math.PI) * 360.0).toInt()
+
+        return SatPassTime(
+            startDate, endDate, tca, polePassed, aosAzimuth,
+            losAzimuth, maxElevation / (2.0 * Math.PI) * 360.0
+        )
+    }
+
+    private fun getPosition(cal: Calendar, offSet: Int): SatPos {
+        cal.add(Calendar.SECOND, offSet)
+        return getSatPos(cal.time)
+    }
+
+    private fun getPolePassed(prevPos: SatPos, satPos: SatPos): String {
+        var polePassed = deadSpotNone
+        val az1 = prevPos.azimuth / twoPi * 360.0
+        val az2 = satPos.azimuth / twoPi * 360.0
+        if (az1 > az2) { // we may be moving from 350 or greater through north
+            if (az1 > 350 && az2 < 10) polePassed = north
+            else { // we may be moving from 190 or greater through south
+                if (az1 > 180 && az2 < 180) polePassed = south
+            }
+        } else { // we may be moving from 10 or less through north
+            if (az1 < 10 && az2 > 350) polePassed = north
+            else { // we may be moving from 170 or more through south
+                if (az1 < 180 && az2 > 180) polePassed = south
+            }
+        }
+        return polePassed
+    }
+
+    private fun threeQuarterOrbitMinutes(): Int {
+        return (24.0 * 60.0 / tle.meanmo * 0.75).toInt()
+    }
+}