Further changes to Look4Sat Predictor.kt core class

2021-09-16 10:03:58 +01:00
1 parent bceeb01194
commit a82915c0ca
@@ -1,388 +0,0 @@
-/*
- * Look4Sat. Amateur radio satellite tracker and pass predictor.
- * Copyright (C) 2019-2021 Arty Bishop (bishop.arty@gmail.com)
- *
- * 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 3 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, see <https://www.gnu.org/licenses/>.
- */
-package com.rtbishop.look4sat.data
-
-import com.rtbishop.look4sat.domain.*
-import kotlinx.coroutines.CoroutineDispatcher
-import kotlinx.coroutines.flow.MutableSharedFlow
-import kotlinx.coroutines.flow.SharedFlow
-import kotlinx.coroutines.withContext
-import java.util.*
-import kotlin.math.max
-import kotlin.math.min
-import kotlin.math.pow
-import kotlin.math.sqrt
-
-class PassPredictor(private val defaultDispatcher: CoroutineDispatcher) {
-
-    // Radar view - beacon
-    private val _skyPosition = MutableSharedFlow<SatPos>(replay = 1)
-    val skyPosition: SharedFlow<SatPos> = _skyPosition
-
-    suspend fun getSkyPosition(pass: SatPass, stationPos: StationPos, date: Date) {
-        withContext(defaultDispatcher) {
-            _skyPosition.emit(pass.satellite.getPosition(stationPos, date.time))
-        }
-    }
-
-    // Radar view - track
-    private val _skyTrack = MutableSharedFlow<List<SatPos>>(replay = 1)
-    val skyTrack: SharedFlow<List<SatPos>> = _skyTrack
-
-    suspend fun getSkyTrack(pass: SatPass, stationPos: StationPos) {
-        withContext(defaultDispatcher) {
-            val positions = mutableListOf<SatPos>()
-            var currentTime = pass.aosTime
-            while (currentTime < pass.losTime) {
-                positions.add(pass.satellite.getPosition(stationPos, currentTime))
-                currentTime += 15000
-            }
-            _skyTrack.emit(positions)
-        }
-    }
-
-    // Map view - beacons
-    private val _mapPositions = MutableSharedFlow<Map<Satellite, GeoPos>>(replay = 1)
-    val mapPositions: SharedFlow<Map<Satellite, GeoPos>> = _mapPositions
-
-    suspend fun getMapPositions(satellites: List<Satellite>, stationPos: StationPos, date: Date) {
-        withContext(defaultDispatcher) {
-            val positions = mutableMapOf<Satellite, GeoPos>()
-            satellites.forEach { satellite ->
-                val satPos = satellite.getPosition(stationPos, date.time)
-                val osmLat = clipLat(Math.toDegrees(satPos.latitude))
-                val osmLon = clipLon(Math.toDegrees(satPos.longitude))
-                positions[satellite] = GeoPos(osmLat, osmLon)
-            }
-            _mapPositions.emit(positions)
-        }
-    }
-
-    // Map view - track
-    private val _mapTrack = MutableSharedFlow<List<List<GeoPos>>>(replay = 1)
-    val mapTrack: SharedFlow<List<List<GeoPos>>> = _mapTrack
-
-    suspend fun getMapTrack(satellite: Satellite, stationPos: StationPos, date: Date) {
-        withContext(defaultDispatcher) {
-            val positions = mutableListOf<SatPos>()
-            val orbitalPeriod = satellite.getQuarterOrbitMin() * 4
-            val endTime = date.time + (orbitalPeriod * 2.4 * 60L * 1000L).toLong()
-            var currentTime = date.time
-            while (currentTime < endTime) {
-                positions.add(satellite.getPosition(stationPos, currentTime))
-                currentTime += 15000
-            }
-
-            val satTracks = mutableListOf<List<GeoPos>>()
-            val currentTrack = mutableListOf<GeoPos>()
-            var oldLongitude = 0.0
-            positions.forEach { satPos ->
-                val osmLat = clipLat(Math.toDegrees(satPos.latitude))
-                val osmLon = clipLon(Math.toDegrees(satPos.longitude))
-                val currentPos = GeoPos(osmLat, osmLon)
-                if (oldLongitude < -170.0 && currentPos.longitude > 170.0) {
-                    // adding left terminal position
-                    currentTrack.add(GeoPos(osmLat, -180.0))
-                    satTracks.add(mutableListOf<GeoPos>().apply { addAll(currentTrack) })
-                    currentTrack.clear()
-                } else if (oldLongitude > 170.0 && currentPos.longitude < -170.0) {
-                    // adding right terminal position
-                    currentTrack.add(GeoPos(osmLat, 180.0))
-                    satTracks.add(mutableListOf<GeoPos>().apply { addAll(currentTrack) })
-                    currentTrack.clear()
-                }
-                oldLongitude = currentPos.longitude
-                currentTrack.add(currentPos)
-            }
-            satTracks.add(currentTrack)
-            _mapTrack.emit(satTracks)
-        }
-    }
-
-    private val _mapFootprint = MutableSharedFlow<List<GeoPos>>(replay = 1)
-    val mapFootprint: SharedFlow<List<GeoPos>> = _mapFootprint
-
-    suspend fun setSelectedSatFootprint(satellite: Satellite, stationPos: StationPos, date: Date) {
-        withContext(defaultDispatcher) {
-            val satPos = satellite.getPosition(stationPos, date.time)
-            val satFootprint = satPos.getRangeCircle().map { groundPos ->
-                val osmLat = clipLat(groundPos.latitude)
-                val osmLon = clipLon(groundPos.longitude)
-                GeoPos(osmLat, osmLon)
-            }
-            _mapFootprint.emit(satFootprint)
-        }
-    }
-
-    private val _satData = MutableSharedFlow<SatData>(replay = 1)
-    val satData: SharedFlow<SatData> = _satData
-
-    suspend fun setSelectedSatData(satellite: Satellite, stationPos: StationPos, date: Date) {
-        withContext(defaultDispatcher) {
-            val satPos = satellite.getPosition(stationPos, date.time)
-            val osmLat = clipLat(Math.toDegrees(satPos.latitude))
-            val osmLon = clipLon(Math.toDegrees(satPos.longitude))
-            val osmPos = GeoPos(osmLat, osmLon)
-            val qthLoc = QthConverter.positionToQTH(osmPos.latitude, osmPos.longitude) ?: "-- --"
-            val velocity = getOrbitalVelocity(satPos.altitude)
-            val satData = SatData(
-                satellite, satellite.params.catnum, satellite.params.name, satPos.range,
-                satPos.altitude, velocity, qthLoc, osmPos
-            )
-            _satData.emit(satData)
-        }
-    }
-
-    private fun getOrbitalVelocity(altitude: Double): Double {
-        val earthG = 6.674 * 10.0.pow(-11)
-        val earthM = 5.98 * 10.0.pow(24)
-        val radius = 6.37 * 10.0.pow(6) + altitude * 10.0.pow(3)
-        return sqrt(earthG * earthM / radius) / 1000
-    }
-
-    private fun clipLat(pLatitude: Double): Double {
-        return clip(pLatitude, -85.05, 85.05)
-    }
-
-    private fun clipLon(pLongitude: Double): Double {
-        var result = pLongitude
-        while (result < -180.0) result += 360.0
-        while (result > 180.0) result -= 360.0
-        return clip(result, -180.0, 180.0)
-    }
-
-    private fun clip(currentValue: Double, minValue: Double, maxValue: Double): Double {
-        return min(max(currentValue, minValue), maxValue)
-    }
-
-    fun getPositions(
-        satellite: Satellite,
-        stationPos: StationPos,
-        refDate: Date,
-        stepSec: Int,
-        minBefore: Int,
-        orbits: Double
-    ): List<SatPos> {
-        val positions = mutableListOf<SatPos>()
-        val orbitalPeriod = 24 * 60 / satellite.params.meanmo
-        val endDate = Date(refDate.time + (orbitalPeriod * orbits * 60L * 1000L).toLong())
-        val startDate = Date(refDate.time - minBefore * 60L * 1000L)
-        var currentDate = startDate
-        while (currentDate.before(endDate)) {
-            val satPos = satellite.getPosition(stationPos, currentDate.time)
-            positions.add(satPos)
-            currentDate = Date(currentDate.time + stepSec * 1000)
-        }
-        return positions
-    }
-
-    // List view - passes
-    private val _passes = MutableSharedFlow<List<SatPass>>(replay = 1)
-    private var selectedSatellites = emptyList<Satellite>()
-    val passes: SharedFlow<List<SatPass>> = _passes
-
-    suspend fun triggerCalculation(
-        satellites: List<Satellite>,
-        stationPos: StationPos,
-        refDate: Date = Date(),
-        hoursAhead: Int = 8
-    ) {
-        if (satellites.isEmpty()) {
-            _passes.emit(emptyList())
-        } else {
-            val oldCatNums = selectedSatellites.map { it.params.catnum }
-            val newCatNums = satellites.map { it.params.catnum }
-            if (oldCatNums != newCatNums) forceCalculation(
-                satellites,
-                stationPos,
-                refDate,
-                hoursAhead
-            )
-        }
-    }
-
-    suspend fun forceCalculation(
-        satellites: List<Satellite>,
-        stationPos: StationPos,
-        refDate: Date = Date(),
-        hoursAhead: Int = 8
-    ) {
-        if (satellites.isEmpty()) {
-            _passes.emit(emptyList())
-        } else {
-            withContext(defaultDispatcher) {
-                val allPasses = mutableListOf<SatPass>()
-                selectedSatellites = satellites
-                satellites.forEach { satellite ->
-                    val passes = getPasses(satellite, stationPos, refDate, hoursAhead)
-                    allPasses.addAll(passes)
-                }
-                _passes.emit(filterPasses(allPasses, refDate))
-            }
-        }
-    }
-
-    private fun getPasses(
-        satellite: Satellite,
-        stationPos: StationPos,
-        date: Date,
-        hoursAhead: Int
-    ): List<SatPass> {
-        val passes = mutableListOf<SatPass>()
-        val endDate = Date(date.time + hoursAhead * 60L * 60L * 1000L)
-        val quarterOrbitMin = satellite.getQuarterOrbitMin()
-        var startDate = date
-        var shouldWindBack = true
-        var lastAosDate: Date
-        var count = 0
-        if (satellite.willBeSeen(stationPos)) {
-            if (satellite.params.isDeepspace) {
-                passes.add(nextDeepSpacePass(satellite, stationPos, date))
-            } else {
-                do {
-                    if (count > 0) shouldWindBack = false
-                    val pass = nextNearEarthPass(satellite, stationPos, startDate, shouldWindBack)
-                    lastAosDate = Date(pass.aosTime)
-                    passes.add(pass)
-                    startDate = Date(pass.losTime + (quarterOrbitMin * 3) * 60L * 1000L)
-                    count++
-                } while (lastAosDate < endDate)
-            }
-        }
-        return passes
-    }
-
-    private fun filterPasses(
-        passes: List<SatPass>,
-        refDate: Date,
-        hoursAhead: Int = 8,
-        minElevation: Double = 16.0
-    ): List<SatPass> {
-        val timeFuture = refDate.time + (hoursAhead * 3600 * 1000)
-        return passes.filter { it.losTime > refDate.time }
-            .filter { it.aosTime < timeFuture }
-            .filter { it.maxElevation > minElevation }
-            .sortedBy { it.aosTime }
-    }
-
-    private fun nextDeepSpacePass(
-        satellite: Satellite,
-        stationPos: StationPos,
-        refDate: Date
-    ): SatPass {
-        val satPos = satellite.getPosition(stationPos, refDate.time)
-        val aos = Date(refDate.time - 24 * 60L * 60L * 1000L).time
-        val los = Date(refDate.time + 24 * 60L * 60L * 1000L).time
-        val tca = Date((aos + los) / 2).time
-        val az = Math.toDegrees(satPos.azimuth)
-        val elev = Math.toDegrees(satPos.elevation)
-        val alt = satPos.altitude
-        return SatPass(aos, az, los, az, tca, az, alt, elev, satellite)
-    }
-
-    private fun nextNearEarthPass(
-        satellite: Satellite,
-        stationPos: StationPos,
-        refDate: Date,
-        windBack: Boolean = false
-    ): SatPass {
-        val calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC")).apply {
-            clear()
-            timeInMillis = refDate.time
-        }
-        val quarterOrbitMin = satellite.getQuarterOrbitMin()
-
-        var elevation: Double
-        var maxElevation = 0.0
-        var alt = 0.0
-        var tcaAz = 0.0
-
-        // wind back time 1/4 of an orbit
-        if (windBack) calendar.add(Calendar.MINUTE, -quarterOrbitMin)
-        var satPos = satellite.getPosition(stationPos, calendar.time.time)
-
-        if (satPos.elevation > 0.0) {
-            // move forward in 30 second intervals until the sat goes below the horizon
-            do {
-                calendar.add(Calendar.SECOND, 30)
-                satPos = satellite.getPosition(stationPos, calendar.time.time)
-            } while (satPos.elevation > 0.0)
-            // move forward 3/4 of an orbit
-            calendar.add(Calendar.MINUTE, quarterOrbitMin * 3)
-        }
-
-        // find the next time sat comes above the horizon
-        do {
-            calendar.add(Calendar.SECOND, 60)
-            satPos = satellite.getPosition(stationPos, calendar.time.time)
-            elevation = satPos.elevation
-            if (elevation > maxElevation) {
-                maxElevation = elevation
-                alt = satPos.altitude
-                tcaAz = Math.toDegrees(satPos.azimuth)
-            }
-        } while (satPos.elevation < 0.0)
-
-        // refine to 3 seconds
-        calendar.add(Calendar.SECOND, -60)
-        do {
-            calendar.add(Calendar.SECOND, 3)
-            satPos = satellite.getPosition(stationPos, calendar.time.time)
-            elevation = satPos.elevation
-            if (elevation > maxElevation) {
-                maxElevation = elevation
-                alt = satPos.altitude
-                tcaAz = Math.toDegrees(satPos.azimuth)
-            }
-        } while (satPos.elevation < 0.0)
-
-        val aos = satPos.time
-        val aosAz = Math.toDegrees(satPos.azimuth)
-
-        // find when sat goes below
-        do {
-            calendar.add(Calendar.SECOND, 30)
-            satPos = satellite.getPosition(stationPos, calendar.time.time)
-            elevation = satPos.elevation
-            if (elevation > maxElevation) {
-                maxElevation = elevation
-                alt = satPos.altitude
-                tcaAz = Math.toDegrees(satPos.azimuth)
-            }
-        } while (satPos.elevation > 0.0)
-
-        // refine to 3 seconds
-        calendar.add(Calendar.SECOND, -30)
-        do {
-            calendar.add(Calendar.SECOND, 3)
-            satPos = satellite.getPosition(stationPos, calendar.time.time)
-            elevation = satPos.elevation
-            if (elevation > maxElevation) {
-                maxElevation = elevation
-                alt = satPos.altitude
-                tcaAz = Math.toDegrees(satPos.azimuth)
-            }
-        } while (satPos.elevation > 0.0)
-
-        val los = satPos.time
-        val losAz = Math.toDegrees(satPos.azimuth)
-        val tca = Date((aos + los) / 2).time
-        val elev = Math.toDegrees(maxElevation)
-        return SatPass(aos, aosAz, los, losAz, tca, tcaAz, alt, elev, satellite)
-    }
-}
@@ -0,0 +1,214 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2021 Arty Bishop (bishop.arty@gmail.com)
+ *
+ * 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 3 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, see <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.domain
+
+import com.rtbishop.look4sat.domain.*
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.SharedFlow
+import kotlinx.coroutines.withContext
+import java.util.*
+
+class Predictor(private val predictorDispatcher: CoroutineDispatcher) {
+
+    private val _passes = MutableSharedFlow<List<SatPass>>(replay = 1)
+    private var selectedSatIds = emptyList<Int>()
+    val passes: SharedFlow<List<SatPass>> = _passes
+
+    suspend fun getSatPos(sat: Satellite, pos: StationPos, date: Date): SatPos =
+        withContext(predictorDispatcher) {
+            return@withContext sat.getPosition(pos, date.time)
+        }
+
+    suspend fun getSatTrack(sat: Satellite, pos: StationPos, start: Date, end: Date): List<SatPos> =
+        withContext(predictorDispatcher) {
+            val positions = mutableListOf<SatPos>()
+            var currentTime = start.time
+            while (currentTime < end.time) {
+                positions.add(sat.getPosition(pos, currentTime))
+                currentTime += 15000
+            }
+            return@withContext positions
+        }
+
+    suspend fun triggerCalculation(
+        satellites: List<Satellite>,
+        pos: StationPos,
+        date: Date = Date(),
+        hoursAhead: Int = 8,
+        minElevation: Double = 16.0
+    ) {
+        if (satellites.isEmpty()) {
+            _passes.emit(emptyList())
+        } else {
+            val newCatNums = satellites.map { it.params.catnum }
+            if (selectedSatIds != newCatNums) {
+                forceCalculation(satellites, pos, date, hoursAhead, minElevation)
+            }
+        }
+    }
+
+    suspend fun forceCalculation(
+        satellites: List<Satellite>,
+        pos: StationPos,
+        date: Date = Date(),
+        hoursAhead: Int = 8,
+        minElevation: Double = 16.0
+    ) {
+        if (satellites.isEmpty()) {
+            _passes.emit(emptyList())
+        } else {
+            withContext(predictorDispatcher) {
+                val allPasses = mutableListOf<SatPass>()
+                selectedSatIds = satellites.map { it.params.catnum }
+                satellites.forEach { satellite ->
+                    allPasses.addAll(satellite.getPasses(pos, date, hoursAhead))
+                }
+                _passes.emit(allPasses.filter(date, hoursAhead, minElevation))
+            }
+        }
+    }
+
+    private fun Satellite.getPasses(pos: StationPos, date: Date, hours: Int): List<SatPass> {
+        val passes = mutableListOf<SatPass>()
+        val endDate = Date(date.time + hours * 60L * 60L * 1000L)
+        val quarterOrbitMin = (this.orbitalPeriod / 4.0).toInt()
+        var startDate = date
+        var shouldRewind = true
+        var lastAosDate: Date
+        var count = 0
+        if (this.willBeSeen(pos)) {
+            if (this.params.isDeepspace) {
+                passes.add(getGeoPass(this, pos, date))
+            } else {
+                do {
+                    if (count > 0) shouldRewind = false
+                    val pass = getLeoPass(this, pos, startDate, shouldRewind)
+                    lastAosDate = Date(pass.aosTime)
+                    passes.add(pass)
+                    startDate = Date(pass.losTime + (quarterOrbitMin * 3) * 60L * 1000L)
+                    count++
+                } while (lastAosDate < endDate)
+            }
+        }
+        return passes
+    }
+
+    private fun List<SatPass>.filter(date: Date, hoursAhead: Int, minElev: Double): List<SatPass> {
+        val timeFuture = date.time + (hoursAhead * 60L * 60L * 1000L)
+        return this.filter { it.losTime > date.time }
+            .filter { it.aosTime < timeFuture }
+            .filter { it.maxElevation > minElev }
+            .sortedBy { it.aosTime }
+    }
+
+    private fun getGeoPass(sat: Satellite, pos: StationPos, date: Date): SatPass {
+        val satPos = sat.getPosition(pos, date.time)
+        val aos = Date(date.time - 24 * 60L * 60L * 1000L).time
+        val los = Date(date.time + 24 * 60L * 60L * 1000L).time
+        val tca = Date((aos + los) / 2).time
+        val az = Math.toDegrees(satPos.azimuth)
+        val elev = Math.toDegrees(satPos.elevation)
+        val alt = satPos.altitude
+        return SatPass(aos, az, los, az, tca, az, alt, elev, sat)
+    }
+
+    private fun getLeoPass(sat: Satellite, pos: StationPos, date: Date, rewind: Boolean): SatPass {
+        val quarterOrbitMin = (sat.orbitalPeriod / 4.0).toInt()
+        val calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC")).apply {
+            clear()
+            timeInMillis = date.time
+        }
+        var elevation: Double
+        var maxElevation = 0.0
+        var alt = 0.0
+        var tcaAz = 0.0
+        // rewind 1/4 of an orbit
+        if (rewind) calendar.add(Calendar.MINUTE, -quarterOrbitMin)
+
+        var satPos = sat.getPosition(pos, calendar.time.time)
+        if (satPos.elevation > 0.0) {
+            // move forward in 30 second intervals until the sat goes below the horizon
+            do {
+                calendar.add(Calendar.SECOND, 30)
+                satPos = sat.getPosition(pos, calendar.time.time)
+            } while (satPos.elevation > 0.0)
+            // move forward 3/4 of an orbit
+            calendar.add(Calendar.MINUTE, quarterOrbitMin * 3)
+        }
+
+        // find the next time sat comes above the horizon
+        do {
+            calendar.add(Calendar.SECOND, 60)
+            satPos = sat.getPosition(pos, calendar.time.time)
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                alt = satPos.altitude
+                tcaAz = Math.toDegrees(satPos.azimuth)
+            }
+        } while (satPos.elevation < 0.0)
+
+        // refine to 3 seconds
+        calendar.add(Calendar.SECOND, -60)
+        do {
+            calendar.add(Calendar.SECOND, 3)
+            satPos = sat.getPosition(pos, calendar.time.time)
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                alt = satPos.altitude
+                tcaAz = Math.toDegrees(satPos.azimuth)
+            }
+        } while (satPos.elevation < 0.0)
+
+        val aos = satPos.time
+        val aosAz = Math.toDegrees(satPos.azimuth)
+
+        // find when sat goes below
+        do {
+            calendar.add(Calendar.SECOND, 30)
+            satPos = sat.getPosition(pos, calendar.time.time)
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                alt = satPos.altitude
+                tcaAz = Math.toDegrees(satPos.azimuth)
+            }
+        } while (satPos.elevation > 0.0)
+
+        // refine to 3 seconds
+        calendar.add(Calendar.SECOND, -30)
+        do {
+            calendar.add(Calendar.SECOND, 3)
+            satPos = sat.getPosition(pos, calendar.time.time)
+            elevation = satPos.elevation
+            if (elevation > maxElevation) {
+                maxElevation = elevation
+                alt = satPos.altitude
+                tcaAz = Math.toDegrees(satPos.azimuth)
+            }
+        } while (satPos.elevation > 0.0)
+
+        val los = satPos.time
+        val losAz = Math.toDegrees(satPos.azimuth)
+        val tca = Date((aos + los) / 2).time
+        val elev = Math.toDegrees(maxElevation)
+        return SatPass(aos, aosAz, los, losAz, tca, tcaAz, alt, elev, sat)
+    }
+}
@@ -41,6 +41,13 @@ data class SatPos(
        return (freq.toDouble() * (speedOfLight + this.rangeRate * 1000.0) / speedOfLight).toLong()
    }

+    fun getOrbitalVelocity(): Double {
+        val earthG = 6.674 * 10.0.pow(-11)
+        val earthM = 5.98 * 10.0.pow(24)
+        val radius = 6.37 * 10.0.pow(6) + altitude * 10.0.pow(3)
+        return sqrt(earthG * earthM / radius) / 1000
+    }
+
    fun getRangeCircle(): List<GeoPos> {
        val positions = mutableListOf<GeoPos>()
        val lat = this.latitude
@@ -31,26 +31,24 @@ abstract class Satellite(val params: TLE) {
    private val position = Vector4()
    private val velocity = Vector4()
    private var perigee = 0.0
+    val orbitalPeriod = 24 * 60 / params.meanmo
    val earthRadius = 6378.137
    val j3Harmonic = -2.53881E-6
    val twoPi = Math.PI * 2.0
    val twoThirds = 2.0 / 3.0
+    val xke = 7.43669161E-2
    val ck2 = 5.413079E-4
    val ck4 = 6.209887E-7
    var qoms24 = 0.0
    var s4 = 0.0
-    val xke = 7.43669161E-2
-
-    fun getQuarterOrbitMin(): Int {
-        return (24.0 * 60.0 / params.meanmo / 4.0).toInt()
-    }

    fun willBeSeen(pos: StationPos): Boolean {
-        return if (params.meanmo < 1e-8) false else {
-            var lin = params.incl
-            if (lin >= 90.0) lin = 180.0 - lin
+        return if (params.meanmo < 1e-8) false
+        else {
            val sma = 331.25 * exp(ln(1440.0 / params.meanmo) * (2.0 / 3.0))
            val apogee = sma * (1.0 + params.eccn) - earthRadius
+            var lin = params.incl
+            if (lin >= 90.0) lin = 180.0 - lin
            acos(earthRadius / (apogee + earthRadius)) + lin * deg2Rad > abs(pos.latitude * deg2Rad)
        }
    }
@@ -71,8 +69,7 @@ abstract class Satellite(val params: TLE) {
        // Angles in rads, dist in km, vel in km/S. Calculate sat Az, El, Range and Range-rate.
        calculateObs(julUTC, position, velocity, pos, squintVector, satPos)
        calculateLatLonAlt(julUTC, satPos, position)
-        satPos.time = time
-        return satPos
+        return satPos.apply { this.time = time }
    }

    // Read the system clock and return the number of days since 31Dec79 00:00:00 UTC (daynum 0)