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Grids - rectangle grid (#121)
* Ported turf grids squareGrid function * Apply suggestions from code review * Fixed MaxLineLength detect issue --------- Co-authored-by: Derek Ellis <[email protected]>
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‎turf/src/commonMain/kotlin/io/github/dellisd/spatialk/turf/Grids.kt‎

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package io.github.dellisd.spatialk.turf
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import io.github.dellisd.spatialk.geojson.BoundingBox
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import io.github.dellisd.spatialk.geojson.Feature
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import io.github.dellisd.spatialk.geojson.FeatureCollection
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import io.github.dellisd.spatialk.geojson.Polygon
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import io.github.dellisd.spatialk.geojson.Position
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import kotlin.math.abs
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import kotlin.math.floor
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/**
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* Creates a rectangle grid within a [BoundingBox].
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*
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* @param [BoundingBox] bbox extent
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* @param double cellWidth of each cell, in units
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* @param double cellHeight of each cell, in units
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* @param units The unit of measurement of the cellSide length
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* @returns [FeatureCollection] a grid of polygons
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*/
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@ExperimentalTurfApi
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fun rectangleGrid(
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bbox: BoundingBox,
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cellWidth: Double,
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cellHeight: Double,
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units: Units = Units.Kilometers
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): FeatureCollection {
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val featureList = mutableListOf<Feature>()
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val west = bbox.southwest.longitude
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val south = bbox.southwest.latitude
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val east = bbox.northeast.longitude
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val north = bbox.northeast.latitude
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val bboxWidth = east - west
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val cellWidthDeg = convertLength(cellWidth, units, Units.Degrees)
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val bboxHeight = north - south;
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val cellHeightDeg = convertLength(cellHeight, units, Units.Degrees);
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val columns = floor(abs(bboxWidth) / cellWidthDeg)
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val rows = floor(abs(bboxHeight) / cellHeightDeg)
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val deltaX = (bboxWidth - columns * cellWidthDeg) / 2
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val deltaY = (bboxHeight - rows * cellHeightDeg) / 2
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var currentX = west + deltaX
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repeat (columns.toInt()) {
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var currentY = south + deltaY
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repeat (rows.toInt()) {
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val positions = mutableListOf<Position>().apply {
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add(Position(currentX, currentY))
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add(Position(currentX, currentY + cellHeightDeg))
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add(Position(currentX + cellWidthDeg, currentY + cellHeightDeg))
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add(Position(currentX + cellWidthDeg, currentY))
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add(Position(currentX, currentY))
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}
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mutableListOf<List<Position>>().apply {
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add(positions)
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}.also {
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featureList.add(Feature(Polygon(it)))
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}
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currentY += cellHeightDeg;
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}
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currentX += cellWidthDeg;
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}
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return FeatureCollection(featureList)
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}

‎turf/src/commonMain/kotlin/io/github/dellisd/spatialk/turf/Measurement.kt‎

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@@ -243,7 +243,7 @@ fun bbox(feature: Feature): BoundingBox = computeBbox(feature.coordAll() ?: empt
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fun bbox(featureCollection: FeatureCollection): BoundingBox = computeBbox(featureCollection.coordAll())
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@Suppress("MagicNumber")
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private fun computeBbox(coordinates: List<Position>): BoundingBox {
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fun computeBbox(coordinates: List<Position>): BoundingBox {
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val result = doubleArrayOf(
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Double.POSITIVE_INFINITY,
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Double.POSITIVE_INFINITY,

‎turf/src/commonTest/kotlin/io/github/dellisd/spatialk/turf/GridsTest.kt‎

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package io.github.dellisd.spatialk.turf
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import io.github.dellisd.spatialk.geojson.BoundingBox
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import io.github.dellisd.spatialk.geojson.FeatureCollection
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import io.github.dellisd.spatialk.geojson.Polygon
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import io.github.dellisd.spatialk.geojson.Position
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import io.github.dellisd.spatialk.turf.utils.readResource
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import kotlin.test.BeforeTest
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import kotlin.test.Test
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import kotlin.test.assertEquals
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class GridsTest {
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private lateinit var box: BoundingBox
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@BeforeTest
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fun before() {
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Polygon.fromJson(readResource("grids/bbox.json")).also {
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box = computeBbox(it.coordinates[0])
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}
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}
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@OptIn(ExperimentalTurfApi::class)
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@Test
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fun testRectangleGrid() {
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rectangleGrid(bbox = box, cellWidth = 200.0, cellHeight = 200.0, units = Units.Meters).also {
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verifyValidGrid(it)
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}
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}
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@OptIn(ExperimentalTurfApi::class)
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@Test
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fun testRectangleGridSameCellSizeButDifferentUnitWillHaveSameResult() {
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rectangleGrid(bbox = box, cellWidth = 0.2, cellHeight = 0.2, units = Units.Kilometers).also {
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verifyValidGrid(it)
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}
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}
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@OptIn(ExperimentalTurfApi::class)
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@Test
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fun defaultUnitsValueIsKilometers() {
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rectangleGrid(bbox = box, cellWidth = 0.2, cellHeight = 0.2).also {
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verifyValidGrid(it)
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}
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}
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@OptIn(ExperimentalTurfApi::class)
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private fun verifyValidGrid(grid: FeatureCollection) {
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assertEquals(16, grid.features.size)
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val expectedFistItem = mutableListOf(
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Position(13.170147683370761, 52.515969323342695),
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Position(13.170147683370761, 52.517765865),
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Position(13.17194422502807, 52.517765865),
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Position(13.17194422502807, 52.515969323342695),
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Position(13.170147683370761, 52.515969323342695))
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assertEquals(expectedFistItem, grid.features.first().geometry!!.coordAll())
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val expectedLastItem = mutableListOf(
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Position(13.18272347497193, 52.517765865),
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Position(13.18272347497193, 52.51956240665731),
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Position(13.18452001662924, 52.51956240665731),
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Position(13.18452001662924, 52.517765865),
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Position(13.18272347497193, 52.517765865))
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assertEquals(expectedLastItem, grid.features.last().geometry!!.coordAll())
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}
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@OptIn(ExperimentalTurfApi::class)
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@Test
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fun cellSizeBiggerThanBboxExtendLeadIntoEmptyGrid() {
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rectangleGrid(bbox = box, cellWidth = 2000.0, cellHeight = 2000.0, units = Units.Meters).also {
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assertEquals(0, it.features.size)
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}
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}
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@OptIn(ExperimentalTurfApi::class)
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@Test
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fun smallerCellSizeWillOutputMoreCellsInGrid() {
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rectangleGrid(bbox = box, cellWidth = 0.1, cellHeight = 0.1).also {
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assertEquals(85, it.features.size)
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}
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}
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@OptIn(ExperimentalTurfApi::class)
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@Test
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fun increasedCellSizeWillOutputLessCellsInGrid() {
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rectangleGrid(bbox = box, cellWidth = 0.3, cellHeight = 0.3).also {
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assertEquals(5, it.features.size)
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}
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}
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}

‎turf/src/commonTest/resources/grids/bbox.json‎

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{
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"type": "Polygon",
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"coordinates": [
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[
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[
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13.16949919,
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52.51513922
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],
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[
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13.16949919,
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52.52039251
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],
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[
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13.18516851,
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52.52039251
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],
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[
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13.18516851,
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52.51513922
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],
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[
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13.16949919,
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52.51513922
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]
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]
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],
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"crs": {
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"type": "name",
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"properties": {
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"name": "EPSG:3857"
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}
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}
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}

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