feat: dual-station radar track plot (satlover/satmatch style)

- MutualPass now carries TrackSample (azimuth/elevation for both stations)
- New MutualRadarView: polar plot with elevation rings (30/60/90),
  cardinal spokes, solid A-track vs dashed B-track, AOS/LOS markers
- Shown in expanded mutual pass card and radar page mutual card

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualPass.kt

@@ -27,6 +27,7 @@ package com.rtbishop.look4sat.feature.mutual
  * @param maxElevationA Peak elevation for station A
  * @param maxElevationB Peak elevation for station B
  * @param elevationSamples List of (time, (elevationA, elevationB)) pairs
+ * @param trackSamples List of radar-track samples (azimuth/elevation for both stations, degrees)
  */
 data class MutualPass(
     val catNum: Int,
@@ -35,5 +36,18 @@ data class MutualPass(
     val endTime: Long,
     val maxElevationA: Double,
     val maxElevationB: Double,
-    val elevationSamples: List<Pair<Long, Pair<Double, Double>>>
+    val elevationSamples: List<Pair<Long, Pair<Double, Double>>>,
+    val trackSamples: List<TrackSample> = emptyList()
+)
+
+/**
+ * One radar-track sample: satellite position as seen from both stations.
+ * All angles are in degrees.
+ */
+data class TrackSample(
+    val time: Long,
+    val azimuthA: Double,
+    val elevationA: Double,
+    val azimuthB: Double,
+    val elevationB: Double
 )

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualRadarView.kt

@@ -0,0 +1,192 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * 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.feature.mutual
+
+import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.graphics.PathEffect
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.graphics.drawscope.Stroke
+import androidx.compose.ui.text.TextMeasurer
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.drawText
+import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import kotlin.math.PI
+import kotlin.math.cos
+import kotlin.math.sin
+
+private const val CIRCLES = 3 // 30°, 60°, 90° rings
+private const val STROKE_WIDTH = 2.5f
+
+/**
+ * Polar radar chart showing the satellite track as seen from both stations
+ * on one plot. Station A is drawn solid, station B dashed.
+ */
+@Composable
+fun MutualRadarView(
+    trackSamples: List<TrackSample>,
+    labelA: String = "站点A",
+    labelB: String = "站点B",
+    modifier: Modifier = Modifier
+) {
+    if (trackSamples.isEmpty()) return
+
+    val colorA = MaterialTheme.colorScheme.primary
+    val colorB = MaterialTheme.colorScheme.tertiary
+    val gridColor = MaterialTheme.colorScheme.outlineVariant
+    val textColor = MaterialTheme.colorScheme.onSurfaceVariant
+    val measurer = rememberTextMeasurer()
+
+    Column(modifier = modifier.fillMaxWidth()) {
+        Canvas(
+            modifier = Modifier
+                .fillMaxWidth()
+                .aspectRatio(1f)
+                .padding(4.dp)
+        ) {
+            val radius = size.minDimension / 2f * 0.92f
+            val center = Offset(size.width / 2f, size.height / 2f)
+
+            // Grid: elevation rings + azimuth spokes + cardinal labels
+            drawRadarGrid(center, radius, gridColor, textColor, measurer)
+
+            // Track paths (only the above-horizon arc)
+            val pathA = Path()
+            val pathB = Path()
+            var firstVisibleA = true
+            var firstVisibleB = true
+            trackSamples.forEach { sample ->
+                if (sample.elevationA > 0f) {
+                    val p = sph2Cart(center, sample.azimuthA, sample.elevationA, radius)
+                    if (firstVisibleA) {
+                        pathA.moveTo(p.x, p.y)
+                        firstVisibleA = false
+                    } else {
+                        pathA.lineTo(p.x, p.y)
+                    }
+                }
+                if (sample.elevationB > 0f) {
+                    val p = sph2Cart(center, sample.azimuthB, sample.elevationB, radius)
+                    if (firstVisibleB) {
+                        pathB.moveTo(p.x, p.y)
+                        firstVisibleB = false
+                    } else {
+                        pathB.lineTo(p.x, p.y)
+                    }
+                }
+            }
+
+            // Solid line for station A, dashed for station B
+            drawPath(pathA, colorA, style = Stroke(STROKE_WIDTH))
+            drawPath(
+                pathB, colorB,
+                style = Stroke(STROKE_WIDTH, pathEffect = PathEffect.dashPathEffect(floatArrayOf(14f, 10f)))
+            )
+
+            // AOS / LOS markers on both tracks
+            val first = trackSamples.first()
+            val last = trackSamples.last()
+            val aosA = sph2Cart(center, first.azimuthA, first.elevationA, radius)
+            val aosB = sph2Cart(center, first.azimuthB, first.elevationB, radius)
+            val losA = sph2Cart(center, last.azimuthA, last.elevationA, radius)
+            val losB = sph2Cart(center, last.azimuthB, last.elevationB, radius)
+            // AOS: hollow circle, LOS: filled circle
+            if (first.elevationA > 0f) drawCircle(colorA, 7f, aosA, style = Stroke(2.5f))
+            if (first.elevationB > 0f) drawCircle(colorB, 7f, aosB, style = Stroke(2.5f))
+            if (last.elevationA > 0f) drawCircle(colorA, 5f, losA)
+            if (last.elevationB > 0f) drawCircle(colorB, 5f, losB)
+
+            // Center dot
+            drawCircle(gridColor, 4f, center)
+        }
+
+        // Legend
+        Row(
+            modifier = Modifier.fillMaxWidth().padding(horizontal = 8.dp, vertical = 4.dp),
+            horizontalArrangement = Arrangement.SpaceEvenly
+        ) {
+            Text("● $labelA", color = colorA, fontSize = 12.sp)
+            Text("- - $labelB", color = colorB, fontSize = 12.sp)
+        }
+    }
+}
+
+private fun DrawScope.drawRadarGrid(
+    center: Offset,
+    radius: Float,
+    color: Color,
+    textColor: Color,
+    measurer: TextMeasurer
+) {
+    // Elevation rings: 30°, 60°, 90°(center) — outer edge is horizon (0°)
+    val step = radius / CIRCLES
+    for (i in 0 until CIRCLES) {
+        drawCircle(color, radius - step * i, center, style = Stroke(1.5f))
+    }
+    // Cardinal spokes
+    drawLine(color, Offset(center.x - radius, center.y), Offset(center.x + radius, center.y), 1.5f)
+    drawLine(color, Offset(center.x, center.y - radius), Offset(center.x, center.y + radius), 1.5f)
+    // Diagonal spokes (lighter)
+    val diag = radius * 0.7071f
+    drawLine(
+        color.copy(alpha = 0.5f),
+        Offset(center.x - diag, center.y - diag), Offset(center.x + diag, center.y + diag), 1f
+    )
+    drawLine(
+        color.copy(alpha = 0.5f),
+        Offset(center.x - diag, center.y + diag), Offset(center.x + diag, center.y - diag), 1f
+    )
+
+    // Elevation ring labels
+    val style = TextStyle(color = textColor, fontSize = 11.sp)
+    for (i in 0 until CIRCLES) {
+        val deg = 30 * (CIRCLES - i)
+        val y = (center.y - (radius - step * i)) - 24f
+        drawText(measurer, "$deg°", Offset(center.x + 6f, y), style = style)
+    }
+    // Cardinal labels
+    drawText(measurer, "N", Offset(center.x - 8f, center.y - radius - 20f), style = style)
+    drawText(measurer, "E", Offset(center.x + radius + 4f, center.y - 10f), style = style)
+    drawText(measurer, "S", Offset(center.x - 6f, center.y + radius + 2f), style = style)
+    drawText(measurer, "W", Offset(center.x - radius - 24f, center.y - 10f), style = style)
+}
+
+/** Convert azimuth (deg, 0=N, clockwise) and elevation (deg) to canvas offset. */
+private fun sph2Cart(center: Offset, azimDeg: Double, elevDeg: Double, r: Float): Offset {
+    val azimRad = azimDeg * PI / 180.0
+    val elevRad = elevDeg * PI / 180.0
+    val radius = r * (PI / 2 - elevRad) / (PI / 2)
+    return Offset(
+        x = center.x + (radius * cos(PI / 2 - azimRad)).toFloat(),
+        y = center.y - (radius * sin(PI / 2 - azimRad)).toFloat()
+    )
+}

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualScreen.kt

@@ -58,6 +58,7 @@ import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import com.rtbishop.look4sat.core.domain.repository.MutualPassData
+import com.rtbishop.look4sat.core.domain.repository.TrackSampleData
 import com.rtbishop.look4sat.core.presentation.IconCard
 import com.rtbishop.look4sat.core.presentation.R
 import com.rtbishop.look4sat.core.presentation.ScreenColumn
@@ -326,6 +327,14 @@ private fun MutualContent(
         itemsIndexed(state.mutualPasses) { index, pass ->
             val mutualData = MutualPassData(
                 samples = pass.elevationSamples,
+                trackSamples = pass.trackSamples.map {
+                    TrackSampleData(
+                        azimuthA = it.azimuthA,
+                        elevationA = it.elevationA,
+                        azimuthB = it.azimuthB,
+                        elevationB = it.elevationB
+                    )
+                },
                 startTime = pass.startTime,
                 endTime = pass.endTime,
                 maxElev = maxOf(pass.maxElevationA, pass.maxElevationB, 10.0),
@@ -399,6 +408,21 @@ private fun MutualPassCard(
             ) {
                 Column {
                     HorizontalDivider(modifier = Modifier.padding(vertical = 8.dp))
+                    // Dual-station radar track (polar plot)
+                    if (pass.trackSamples.isNotEmpty()) {
+                        Text(
+                            text = "双方轨迹（雷达图）",
+                            style = MaterialTheme.typography.titleSmall,
+                            fontWeight = FontWeight.Medium,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
+                        MutualRadarView(
+                            trackSamples = pass.trackSamples,
+                            labelA = "你",
+                            labelB = "友台"
+                        )
+                        Spacer(Modifier.height(8.dp))
+                    }
                     if (pass.elevationSamples.isNotEmpty()) {
                         ElevationCurveChart(
                             samples = pass.elevationSamples,

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualViewModel.kt

@@ -224,16 +224,28 @@ class MutualViewModel(
                 val refinedLos = refineEdge(sat, posA, posB, minElevADeg, minElevBDeg, los, step = 1_000L, goingUp = false)
 
                 val samples = mutableListOf<Pair<Long, Pair<Double, Double>>>()
+                val tracks = mutableListOf<TrackSample>()
                 var maxElevA = 0.0
                 var maxElevB = 0.0
 
                 var tSample = refinedAos
                 while (tSample <= refinedLos) {
-                    val elevA = elevationDeg(sat, posA, tSample)
-                    val elevB = elevationDeg(sat, posB, tSample)
+                    val fullA = sat.getFullPosition(posA, tSample)
+                    val fullB = sat.getFullPosition(posB, tSample)
+                    val elevA = fullA.elevation * 180.0 / PI
+                    val elevB = fullB.elevation * 180.0 / PI
                     if (elevA > maxElevA) maxElevA = elevA
                     if (elevB > maxElevB) maxElevB = elevB
                     samples.add(tSample to (elevA to elevB))
+                    tracks.add(
+                        TrackSample(
+                            time = tSample,
+                            azimuthA = fullA.azimuth * 180.0 / PI,
+                            elevationA = elevA,
+                            azimuthB = fullB.azimuth * 180.0 / PI,
+                            elevationB = elevB
+                        )
+                    )
                     tSample += sampleInterval
                 }
 
@@ -246,7 +258,8 @@ class MutualViewModel(
                             endTime = refinedLos,
                             maxElevationA = (maxElevA * 10).roundToInt() / 10.0,
                             maxElevationB = (maxElevB * 10).roundToInt() / 10.0,
-                            elevationSamples = samples
+                            elevationSamples = samples,
+                            trackSamples = tracks
                         )
                     )
                 }