feat(gridfinder): VUCC 网格寻线实地导航 + LoTW 上传台址预填联动 + 移除地图入口

- GridGeometry 网格线/点几何 + QthConverter grid4/grid8；golden vectors 单测
- 独立定位流 ILocationRepo/LocationRepo（stop 时 removeUpdates），不自动写台址
- feature/gridfinder 模块：罗盘表盘、极坐标近距图、线上/点上精度门控（连续 3 次 ≤6.1m）
- 「设为 LoTW 上传台址」：跳证书配置页并预填当前网格（1/2/4 格），只改台站 grid 字段
- 地图页入口移除，设置页单入口；顶部间距改 ScreenColumn 结构（与设置页同构）
- 术语统一「最近网格点」（中英）

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/ILocationRepo.kt

@@ -0,0 +1,65 @@
+/*
+ * 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.core.domain.repository
+
+import kotlinx.coroutines.flow.StateFlow
+
+/**
+ * A single position fix from the device's location provider, with the
+ * horizontal accuracy reported by the platform.
+ */
+data class LocationFix(
+    val latitude: Double,
+    val longitude: Double,
+    val altitudeMeters: Double = 0.0,
+    val accuracyMeters: Float,
+    val epochMs: Long
+) {
+    /** ARRL VUCC work needs a fix good to the 20 ft (6.1 m) rule. */
+    fun isPreciseEnough(limitMeters: Float): Boolean = accuracyMeters in 0f..limitMeters
+}
+
+/** What the live-location source is currently able to give. */
+sealed interface LocationState {
+    /** No fix yet - either permission is missing or the provider is warming up. */
+    data class Waiting(val permissionGranted: Boolean, val providerEnabled: Boolean) : LocationState
+
+    data class Fix(val location: LocationFix) : LocationState
+}
+
+/**
+ * Live device position for field tools (currently the Grid Finder). Kept
+ * separate from [ISettingsRepo.stationPosition] on purpose: collecting fixes
+ * here must never move the user's station, which is what drives every pass
+ * prediction in the app.
+ *
+ * Callers register with [startUpdates] while their screen is alive and MUST
+ * call [stopUpdates] when it goes away.
+ */
+interface ILocationRepo {
+    val state: StateFlow<LocationState>
+
+    /** Whether the app currently holds the fine-location permission. */
+    fun hasPermission(): Boolean
+
+    /** Begins delivering fixes; no-op when permission is missing. */
+    fun startUpdates()
+
+    /** Stops delivering fixes and releases the platform listener. */
+    fun stopUpdates()
+}

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/IMainContainer.kt

@@ -38,8 +38,12 @@ interface IMainContainer {
     val qsoRepository: IQsoRepository
     val lotwUploadRepository: ILoTWUploadRepository
     val radioTrackingService: IRadioTrackingService
+    val locationRepo: ILocationRepo
     val mutualPassData: StateFlow<MutualPassData>
+    /** Grid Finder → LoTW station page prefill, consumed once by that page. */
+    val pendingLoTWStationGrid: StateFlow<String?>
     fun setMutualPassData(data: MutualPassData)
+    fun setPendingLoTWStationGrid(grid: String?)
     fun provideAddToCalendar(): IAddToCalendar
     fun provideShowToast(): IShowToast
     fun provideBluetoothReporter(): IReporter

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/utility/GridGeometry.kt

@@ -0,0 +1,189 @@
+/*
+ * 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.core.domain.utility
+
+import kotlin.math.abs
+import kotlin.math.atan2
+import kotlin.math.cos
+import kotlin.math.hypot
+import kotlin.math.round
+
+/**
+ * Grid-line / grid-corner geometry for the 4-character Maidenhead squares that
+ * VUCC credits, used by the Grid Finder field tool.
+ *
+ * A 4-character square is 1 degree tall (boundaries at integer latitudes) and
+ * 2 degrees wide (boundaries at even offsets from the -180 degree antimeridian),
+ * so a station's distance to the nearest VUCC line and corner is a matter of
+ * simple planar geometry at the station's latitude.
+ *
+ * Geometry ported from OrbitDeck for iOS (MIT License, (c) 2026 Paul Stoetzer,
+ * N8HM) - `GridGeometry` in `Views/HomeView.swift` and `vuccGrids` in
+ * `Engine/FeatureEngine.swift`. Golden values are pinned by GridGeometryTest.
+ */
+
+/** ARRL VUCC "20 ft rule": a fix within this distance of a boundary counts as on it. */
+const val VUCC_BOUNDARY_TOLERANCE_METERS = 20.0 * 0.3048
+
+/** One degree of latitude in metres; 4-character squares are 1 degree tall. */
+private const val METERS_PER_DEGREE_LATITUDE = 111_320.0
+
+/** Nudge used to name the square on the far side of a boundary (display only). */
+private const val NEIGHBOUR_NUDGE_DEGREES = 0.0005
+
+/** Nudge used by [vuccClaimableGrids] so the neighbour lands squarely across. */
+private const val CLAIM_NEIGHBOUR_NUDGE_DEGREES = 0.001
+
+private const val DEG_TO_RAD = 0.017453292519943295
+private const val RAD_TO_DEG = 57.29577951308232
+
+/** Where the nearest 4-character boundary lies relative to the fix. */
+enum class GridBoundaryDirection { NORTH, SOUTH, EAST, WEST }
+
+/** ARRL VUCC standing of a fix, derived from how many squares it may claim. */
+enum class GridFixStatus { INSIDE_GRID, ON_GRID_LINE, ON_GRID_CORNER }
+
+/**
+ * Distance and bearing to the nearest 4-character grid corner and grid line,
+ * plus the locators of the squares that meet there. All distances are metres
+ * computed on a flat approximation local to the fix (the same approximation
+ * the source implementation uses; over the <=100 km distances involved the
+ * error is far below a GPS fix's own accuracy).
+ */
+data class GridGeometry(
+    val grid4: String,
+    val grid6: String,
+    val grid8: String,
+    val latLineMeters: Double,
+    val latLineDirection: GridBoundaryDirection,
+    val lonLineMeters: Double,
+    val lonLineDirection: GridBoundaryDirection,
+    val cornerMeters: Double,
+    val cornerBearingDegrees: Double,
+    val cornerGrids: List<String>,
+    val nearestLineMeters: Double,
+    val nearestLineBearingDegrees: Double,
+    val nearestLineIsLatitude: Boolean,
+    val nearestLineGrids: List<String>
+)
+
+/**
+ * The geometry of the VUCC (4-character) grid around a position, or null when
+ * the position is out of range.
+ */
+fun gridGeometry(latitude: Double, longitude: Double): GridGeometry? {
+    val grid4 = positionToGrid4(latitude, longitude) ?: return null
+    val grid6 = positionToQth(latitude, longitude) ?: return null
+    val grid8 = positionToGrid8(latitude, longitude) ?: return null
+
+    // 4-character boundaries: integer latitudes, even-degree longitudes.
+    val latBoundary = round(latitude)
+    val lonBoundary = round((longitude + 180.0) / 2.0) * 2.0 - 180.0
+
+    val metersPerDegreeLon = METERS_PER_DEGREE_LATITUDE * cos(latitude * DEG_TO_RAD)
+    val dNorth = (latBoundary - latitude) * METERS_PER_DEGREE_LATITUDE
+    val dEast = (lonBoundary - longitude) * metersPerDegreeLon
+
+    val otherLat = latBoundary - if (latitude >= latBoundary) NEIGHBOUR_NUDGE_DEGREES else -NEIGHBOUR_NUDGE_DEGREES
+    val otherLon = lonBoundary - if (longitude >= lonBoundary) NEIGHBOUR_NUDGE_DEGREES else -NEIGHBOUR_NUDGE_DEGREES
+
+    val cornerGrids = setOfNotNull(
+        positionToGrid4(latitude, longitude),
+        positionToGrid4(otherLat, longitude),
+        positionToGrid4(latitude, otherLon),
+        positionToGrid4(otherLat, otherLon)
+    ).sorted()
+
+    val onLatitude = abs(dNorth) <= abs(dEast)
+    val nearestLineGrids = if (onLatitude) {
+        setOfNotNull(grid4, positionToGrid4(otherLat, longitude)).sorted()
+    } else {
+        setOfNotNull(grid4, positionToGrid4(latitude, otherLon)).sorted()
+    }
+
+    return GridGeometry(
+        grid4 = grid4,
+        grid6 = grid6,
+        grid8 = grid8,
+        latLineMeters = abs(dNorth),
+        latLineDirection = if (dNorth >= 0) GridBoundaryDirection.NORTH else GridBoundaryDirection.SOUTH,
+        lonLineMeters = abs(dEast),
+        lonLineDirection = if (dEast >= 0) GridBoundaryDirection.EAST else GridBoundaryDirection.WEST,
+        cornerMeters = hypot(dNorth, dEast),
+        cornerBearingDegrees = bearingDegrees(dNorth, dEast),
+        cornerGrids = cornerGrids,
+        nearestLineMeters = if (onLatitude) abs(dNorth) else abs(dEast),
+        nearestLineBearingDegrees = if (onLatitude) {
+            if (dNorth >= 0) 0.0 else 180.0
+        } else {
+            if (dEast >= 0) 90.0 else 270.0
+        },
+        nearestLineIsLatitude = onLatitude,
+        nearestLineGrids = nearestLineGrids
+    )
+}
+
+/**
+ * The 4-character squares a station at this position may claim under ARRL VUCC
+ * rules: normally one, but two when the fix is on the line between two squares
+ * and four when it is on the corner where four squares meet. A fix within
+ * [toleranceMeters] of a boundary is considered to be on it (the 20 ft rule).
+ */
+fun vuccClaimableGrids(
+    latitude: Double,
+    longitude: Double,
+    toleranceMeters: Double = VUCC_BOUNDARY_TOLERANCE_METERS
+): List<String> {
+    val own = positionToGrid4(latitude, longitude) ?: return emptyList()
+    val grids = mutableSetOf(own)
+
+    val latBoundary = round(latitude)
+    val lonBoundary = round((longitude + 180.0) / 2.0) * 2.0 - 180.0
+    val metersPerDegreeLon = METERS_PER_DEGREE_LATITUDE * cos(latitude * DEG_TO_RAD)
+
+    val onLatitude = abs(latitude - latBoundary) * METERS_PER_DEGREE_LATITUDE <= toleranceMeters
+    val onLongitude = abs(longitude - lonBoundary) * metersPerDegreeLon <= toleranceMeters
+    if (!onLatitude && !onLongitude) return grids.sorted()
+
+    // Step just past the boundary so the neighbour's locator is unambiguous.
+    val otherLat = latBoundary - if (latitude >= latBoundary) CLAIM_NEIGHBOUR_NUDGE_DEGREES else -CLAIM_NEIGHBOUR_NUDGE_DEGREES
+    val otherLon = lonBoundary - if (longitude >= lonBoundary) CLAIM_NEIGHBOUR_NUDGE_DEGREES else -CLAIM_NEIGHBOUR_NUDGE_DEGREES
+
+    if (onLatitude) {
+        positionToGrid4(otherLat, longitude)?.let(grids::add)
+    }
+    if (onLongitude) {
+        positionToGrid4(latitude, otherLon)?.let(grids::add)
+    }
+    if (onLatitude && onLongitude) {
+        positionToGrid4(otherLat, otherLon)?.let(grids::add)
+    }
+    return grids.sorted()
+}
+
+/** VUCC standing implied by the number of squares a fix may claim. */
+fun gridFixStatus(claimableGrids: List<String>): GridFixStatus = when {
+    claimableGrids.size >= 4 -> GridFixStatus.ON_GRID_CORNER
+    claimableGrids.size >= 2 -> GridFixStatus.ON_GRID_LINE
+    else -> GridFixStatus.INSIDE_GRID
+}
+
+private fun bearingDegrees(dNorth: Double, dEast: Double): Double {
+    val bearing = atan2(dEast, dNorth) * RAD_TO_DEG
+    return if (bearing < 0.0) bearing + 360.0 else bearing
+}

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/utility/QthConverter.kt

@@ -69,6 +69,45 @@ fun positionToQth(latitude: Double, longitude: Double): String? {
     return "$lonFirst$latFirst$lonSecond$latSecond$lonThird$latThird"
 }
 
+/**
+ * Convert a position to its 4-char Maidenhead locator (field + square), the
+ * square VUCC credits, upper-cased. Returns null outside the Maidenhead grid
+ * (lat >= 90 is out of range: the top row is 80..90 N). The longitude is
+ * wrapped into [-180, 180) first, so fixes either side of the antimeridian
+ * resolve to the square they are actually in.
+ */
+fun positionToGrid4(latitude: Double, longitude: Double): String? {
+    if (latitude < -90.0 || latitude >= 90.0) return null
+    val normalizedLon = normalizeLongitude(longitude)
+    val fieldLat = ((latitude + 90.0) / 10.0).toInt().coerceIn(0, 17)
+    val fieldLon = ((normalizedLon + 180.0) / 20.0).toInt().coerceIn(0, 17)
+    val subLat = ((latitude + 90.0) % 10.0).toInt()
+    val subLon = ((normalizedLon + 180.0) % 20.0 / 2.0).toInt()
+    return "${'A' + fieldLon}${'A' + fieldLat}$subLon$subLat"
+}
+
+/**
+ * Convert a position to its 8-char Maidenhead locator: the 6-char locator plus
+ * the numeric extended-square pair (the Maidenhead maximum). Returns null for
+ * out-of-range positions.
+ */
+fun positionToGrid8(latitude: Double, longitude: Double): String? {
+    val normalizedLon = normalizeLongitude(longitude)
+    val base = positionToQth(latitude, normalizedLon) ?: return null
+    val latitudeOffset = latitude.coerceIn(-90.0, 89.999999) + 90.0
+    val longitudeOffset = normalizedLon.coerceIn(-180.0, 179.999999) + 180.0
+    val subLon = 2.0 / 24.0
+    val subLat = 1.0 / 24.0
+    val lonDigit = minOf(9, ((longitudeOffset % subLon) / subLon * 10).toInt())
+    val latDigit = minOf(9, ((latitudeOffset % subLat) / subLat * 10).toInt())
+    return "$base$lonDigit$latDigit"
+}
+
+/** Wrap any longitude into [-180, 180). */
+private fun normalizeLongitude(longitude: Double): Double {
+    return ((longitude + 180.0) % 360.0 + 360.0) % 360.0 - 180.0
+}
+
 private fun isValidPosition(lat: Double, lon: Double): Boolean {
     return (lat >= -90.0 && lat <= 90.0) && (lon >= -180.0 && lon <= 360.0)
 }

core/domain/src/test/java/com/rtbishop/look4sat/core/domain/utility/GridGeometryTest.kt

@@ -0,0 +1,171 @@
+/*
+ * 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.core.domain.utility
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Golden values were produced by a line-by-line port of the reference
+ * implementation (OrbitDeck for iOS, MIT) covering four hemispheres/quadrant
+ * cases plus the two awkward longitudes: the Greenwich meridian and the
+ * antimeridian.
+ */
+class GridGeometryTest {
+
+    private val meterDelta = 0.5
+    private val bearingDelta = 0.05
+
+    @Test
+    fun `station at home square reports both boundaries and the corner`() {
+        val geometry = requireNotNull(gridGeometry(22.3542, 113.6250))
+        assertEquals("OL62", geometry.grid4)
+        assertEquals("OL62TI", geometry.grid6)
+        assertEquals("OL62TI55", geometry.grid8)
+        assertEquals(39429.5, geometry.latLineMeters, meterDelta)
+        assertEquals(GridBoundaryDirection.SOUTH, geometry.latLineDirection)
+        assertEquals(38607.9, geometry.lonLineMeters, meterDelta)
+        assertEquals(GridBoundaryDirection.EAST, geometry.lonLineDirection)
+        assertEquals(55183.8, geometry.cornerMeters, meterDelta)
+        assertEquals(135.60, geometry.cornerBearingDegrees, bearingDelta)
+        assertEquals(listOf("OL61", "OL62", "OL71", "OL72"), geometry.cornerGrids)
+        assertEquals(38607.9, geometry.nearestLineMeters, meterDelta)
+        assertEquals(90.0, geometry.nearestLineBearingDegrees, bearingDelta)
+        assertEquals(false, geometry.nearestLineIsLatitude)
+        assertEquals(listOf("OL62", "OL72"), geometry.nearestLineGrids)
+    }
+
+    @Test
+    fun `fix on the 114 east line sits on the boundary itself`() {
+        val geometry = requireNotNull(gridGeometry(22.3542, 114.0000))
+        assertEquals("OL72", geometry.grid4)
+        assertEquals("OL72AI", geometry.grid6)
+        assertEquals("OL72AI05", geometry.grid8)
+        assertEquals(39429.5, geometry.latLineMeters, meterDelta)
+        assertEquals(0.0, geometry.lonLineMeters, meterDelta)
+        assertEquals(39429.5, geometry.cornerMeters, meterDelta)
+        assertEquals(180.00, geometry.cornerBearingDegrees, bearingDelta)
+        assertEquals(listOf("OL62", "OL72"), geometry.nearestLineGrids)
+    }
+
+    @Test
+    fun `fix on the 22 north 114 east corner names all four squares`() {
+        val geometry = requireNotNull(gridGeometry(22.00002, 114.00003))
+        assertEquals("OL72", geometry.grid4)
+        assertEquals(2.2, geometry.latLineMeters, meterDelta)
+        assertEquals(3.1, geometry.lonLineMeters, meterDelta)
+        assertEquals(3.8, geometry.cornerMeters, meterDelta)
+        assertEquals(234.28, geometry.cornerBearingDegrees, bearingDelta)
+        assertEquals(listOf("OL61", "OL62", "OL71", "OL72"), geometry.cornerGrids)
+        assertEquals("OL71", geometry.nearestLineGrids.first())
+    }
+
+    @Test
+    fun `greenwich meridian fix reports a zero distance latitude line to the north`() {
+        val geometry = requireNotNull(gridGeometry(45.0000, -0.0004))
+        assertEquals("IN95", geometry.grid4)
+        assertEquals("IN95XA", geometry.grid6)
+        assertEquals("IN95XA90", geometry.grid8)
+        assertEquals(0.0, geometry.latLineMeters, meterDelta)
+        assertEquals(GridBoundaryDirection.NORTH, geometry.latLineDirection)
+        assertEquals(31.5, geometry.lonLineMeters, meterDelta)
+        assertEquals(listOf("IN94", "IN95", "JN04", "JN05"), geometry.cornerGrids)
+        assertEquals(true, geometry.nearestLineIsLatitude)
+        assertEquals(listOf("IN94", "IN95"), geometry.nearestLineGrids)
+    }
+
+    @Test
+    fun `antimeridian fix wraps into the eastern square`() {
+        val geometry = requireNotNull(gridGeometry(0.05, 179.9998))
+        assertEquals("RJ90", geometry.grid4)
+        assertEquals("RJ90XB", geometry.grid6)
+        assertEquals("RJ90XB92", geometry.grid8)
+        assertEquals(22.3, geometry.lonLineMeters, meterDelta)
+        assertEquals(GridBoundaryDirection.EAST, geometry.lonLineDirection)
+        assertEquals(179.77, geometry.cornerBearingDegrees, bearingDelta)
+        // The corner's four squares straddle the antimeridian, so the western
+        // pair rolls over to the A-series fields.
+        assertEquals(listOf("AI09", "AJ00", "RI99", "RJ90"), geometry.cornerGrids)
+        assertEquals(listOf("AJ00", "RJ90"), geometry.nearestLineGrids)
+    }
+
+    @Test
+    fun `southern hemisphere fix keeps its bearings right way round`() {
+        val geometry = requireNotNull(gridGeometry(-33.86, 151.21))
+        assertEquals("QF56", geometry.grid4)
+        assertEquals("QF56OD", geometry.grid6)
+        assertEquals(15584.8, geometry.latLineMeters, meterDelta)
+        assertEquals(GridBoundaryDirection.SOUTH, geometry.latLineDirection)
+        assertEquals(73027.8, geometry.lonLineMeters, meterDelta)
+        assertEquals(GridBoundaryDirection.EAST, geometry.lonLineDirection)
+        assertEquals(102.05, geometry.cornerBearingDegrees, bearingDelta)
+        assertEquals(180.0, geometry.nearestLineBearingDegrees, bearingDelta)
+    }
+
+    @Test
+    fun `out of range positions yield no geometry`() {
+        assertNull(gridGeometry(90.0, 0.0))
+        assertNull(gridGeometry(-91.0, 0.0))
+    }
+
+    @Test
+    fun `vucc claims one square when the fix is inside`() {
+        assertEquals(listOf("OL62"), vuccClaimableGrids(22.3542, 113.6250))
+        assertEquals(GridFixStatus.INSIDE_GRID, gridFixStatus(vuccClaimableGrids(22.3542, 113.6250)))
+    }
+
+    @Test
+    fun `vucc claims both squares on a line`() {
+        val claimed = vuccClaimableGrids(22.3542, 114.0000)
+        assertEquals(listOf("OL62", "OL72"), claimed)
+        assertEquals(GridFixStatus.ON_GRID_LINE, gridFixStatus(claimed))
+    }
+
+    @Test
+    fun `vucc claims all four squares on a corner`() {
+        val claimed = vuccClaimableGrids(22.00002, 114.00003)
+        assertEquals(listOf("OL61", "OL62", "OL71", "OL72"), claimed)
+        assertEquals(GridFixStatus.ON_GRID_CORNER, gridFixStatus(claimed))
+    }
+
+    @Test
+    fun `vucc claims nothing extra just outside the 20 foot tolerance`() {
+        // Same corner, but ~38 m away: outside the 20 ft (6.096 m) rule.
+        val claimed = vuccClaimableGrids(22.0002, 114.0003)
+        assertEquals(listOf("OL72"), claimed)
+        assertEquals(GridFixStatus.INSIDE_GRID, gridFixStatus(claimed))
+    }
+
+    @Test
+    fun `vucc tolerance boundary is 20 feet`() {
+        assertEquals(6.096, VUCC_BOUNDARY_TOLERANCE_METERS, 0.0001)
+        // 5 m north of the 22 N line: inside the tolerance for a custom, tighter
+        // call, outside it when the caller demands sub-metre precision.
+        assertTrue(vuccClaimableGrids(22.00005, 113.62).size >= 2)
+        assertEquals(1, vuccClaimableGrids(22.00005, 113.62, toleranceMeters = 1.0).size)
+    }
+
+    @Test
+    fun `grid4 ignores longitudes beyond the antimeridian`() {
+        assertNull(positionToGrid4(91.0, 0.0))
+        // A longitude of 200 degrees is the same meridian as -160 degrees.
+        assertEquals(positionToGrid4(30.0, -160.0), positionToGrid4(30.0, 200.0))
+    }
+}