Grids - rectangle grid

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

@@ -0,0 +1,61 @@
+package io.github.dellisd.spatialk.turf
+
+import io.github.dellisd.spatialk.geojson.BoundingBox
+import io.github.dellisd.spatialk.geojson.Feature
+import io.github.dellisd.spatialk.geojson.FeatureCollection
+import io.github.dellisd.spatialk.geojson.Polygon
+import io.github.dellisd.spatialk.geojson.Position
+import kotlin.math.abs
+import kotlin.math.floor
+
+/**
+ * Creates a rectangle grid within a [BoundingBox].
+ *
+ * @param [BoundingBox] bbox extent
+ * @param double cellWidth of each cell, in units
+ * @param double cellHeight of each cell, in units
+ * @param units The unit of measurement of the cellSide length
+ * @returns [FeatureCollection] a grid of polygons
+ */
+@ExperimentalTurfApi
+fun rectangleGrid(bbox: BoundingBox, cellWidth: Double, cellHeight: Double, units: Units = Units.Kilometers): FeatureCollection {
+    val featureList = mutableListOf<Feature>()
+    val west = bbox.southwest.longitude
+    val south = bbox.southwest.latitude
+    val east = bbox.northeast.longitude
+    val north = bbox.northeast.latitude
+
+    val bboxWidth = east - west
+    val cellWidthDeg = convertLength(cellWidth, units, Units.Degrees)
+
+    val bboxHeight = north - south;
+    val cellHeightDeg = convertLength(cellHeight, units, Units.Degrees);
+
+    val columns = floor(abs(bboxWidth) / cellWidthDeg)
+    val rows = floor(abs(bboxHeight) / cellHeightDeg)
+
+    val deltaX = (bboxWidth - columns * cellWidthDeg) / 2
+    val deltaY = (bboxHeight - rows * cellHeightDeg) / 2
+
+    var currentX = west + deltaX
+    repeat (columns.toInt()) {
+        var currentY = south + deltaY
+        repeat (rows.toInt()) {
+            val positions = mutableListOf<Position>().apply {
+                add(Position(currentX, currentY))
+                add(Position(currentX, currentY + cellHeightDeg))
+                add(Position(currentX + cellWidthDeg, currentY + cellHeightDeg))
+                add(Position(currentX + cellWidthDeg, currentY))
+                add(Position(currentX, currentY))
+            }
+            mutableListOf<List<Position>>().apply {
+                add(positions)
+            }.also {
+                featureList.add(Feature(Polygon(it)))
+            }
+            currentY += cellHeightDeg;
+        }
+        currentX += cellWidthDeg;
+    }
+    return FeatureCollection(featureList)
+}

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

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

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

@@ -0,0 +1,88 @@
+package io.github.dellisd.spatialk.turf
+
+import io.github.dellisd.spatialk.geojson.BoundingBox
+import io.github.dellisd.spatialk.geojson.FeatureCollection
+import io.github.dellisd.spatialk.geojson.Polygon
+import io.github.dellisd.spatialk.geojson.Position
+import io.github.dellisd.spatialk.turf.utils.readResource
+import kotlin.test.BeforeTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class GridsTest {
+
+    private lateinit var box: BoundingBox
+
+    @BeforeTest
+    fun before() {
+        Polygon.fromJson(readResource("grids/bbox.json")).also {
+            box = computeBbox(it.coordinates[0])
+        }
+    }
+    @OptIn(ExperimentalTurfApi::class)
+    @Test
+    fun testRectangleGrid() {
+        rectangleGrid(bbox = box, cellWidth = 200.0, cellHeight = 200.0, units = Units.Meters).also {
+            verifyValidGrid(it)
+        }
+    }
+
+    @OptIn(ExperimentalTurfApi::class)
+    @Test
+    fun testRectangleGridSameCellSizeButDifferentUnitWillHaveSameResult() {
+        rectangleGrid(bbox = box, cellWidth = 0.2, cellHeight = 0.2, units = Units.Kilometers).also {
+            verifyValidGrid(it)
+        }
+    }
+
+    @OptIn(ExperimentalTurfApi::class)
+    @Test
+    fun defaultUnitsValueIsKilometers() {
+        rectangleGrid(bbox = box, cellWidth = 0.2, cellHeight = 0.2).also {
+            verifyValidGrid(it)
+        }
+    }
+
+    @OptIn(ExperimentalTurfApi::class)
+    private fun verifyValidGrid(grid: FeatureCollection) {
+        assertEquals(16, grid.features.size)
+        val expectedFistItem = mutableListOf(
+            Position(13.170147683370761, 52.515969323342695),
+            Position(13.170147683370761, 52.517765865),
+            Position(13.17194422502807, 52.517765865),
+            Position(13.17194422502807, 52.515969323342695),
+            Position(13.170147683370761, 52.515969323342695))
+        assertEquals(expectedFistItem, grid.features.first().geometry!!.coordAll())
+        val expectedLastItem = mutableListOf(
+            Position(13.18272347497193, 52.517765865),
+            Position(13.18272347497193, 52.51956240665731),
+            Position(13.18452001662924, 52.51956240665731),
+            Position(13.18452001662924, 52.517765865),
+            Position(13.18272347497193, 52.517765865))
+        assertEquals(expectedLastItem, grid.features.last().geometry!!.coordAll())
+    }
+
+    @OptIn(ExperimentalTurfApi::class)
+    @Test
+    fun cellSizeBiggerThanBboxExtendLeadIntoEmptyGrid() {
+        rectangleGrid(bbox = box, cellWidth = 2000.0, cellHeight = 2000.0, units = Units.Meters).also {
+            assertEquals(0, it.features.size)
+        }
+    }
+
+    @OptIn(ExperimentalTurfApi::class)
+    @Test
+    fun smallerCellSizeWillOutputMoreCellsInGrid() {
+        rectangleGrid(bbox = box, cellWidth = 0.1, cellHeight = 0.1).also {
+            assertEquals(85, it.features.size)
+        }
+    }
+
+    @OptIn(ExperimentalTurfApi::class)
+    @Test
+    fun increasedCellSizeWillOutputLessCellsInGrid() {
+        rectangleGrid(bbox = box, cellWidth = 0.3, cellHeight = 0.3).also {
+            assertEquals(5, it.features.size)
+        }
+    }
+}

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

@@ -0,0 +1,33 @@
+{
+  "type": "Polygon",
+  "coordinates": [
+    [
+      [
+        13.16949919,
+        52.51513922
+      ],
+      [
+        13.16949919,
+        52.52039251
+      ],
+      [
+        13.18516851,
+        52.52039251
+      ],
+      [
+        13.18516851,
+        52.51513922
+      ],
+      [
+        13.16949919,
+        52.51513922
+      ]
+    ]
+  ],
+  "crs": {
+    "type": "name",
+    "properties": {
+      "name": "EPSG:3857"
+    }
+  }
+}