fix H3 geometry constructor (#374)

* fix H3 geometry constructor

* fix function names

* add test for str function

* lint with scalafmt

* add comments

.jvmopts

@@ -0,0 +1 @@
+-Djts.overlay=ng

src/main/scala/com/databricks/labs/mosaic/core/index/H3IndexSystem.scala

@@ -3,14 +3,15 @@ package com.databricks.labs.mosaic.core.index
 import com.databricks.labs.mosaic.core.geometry.MosaicGeometry
 import com.databricks.labs.mosaic.core.geometry.api.GeometryAPI
 import com.databricks.labs.mosaic.core.types.model.Coordinates
-import com.databricks.labs.mosaic.core.types.model.GeometryTypeEnum.POLYGON
+import com.databricks.labs.mosaic.core.types.model.GeometryTypeEnum.{LINESTRING, POLYGON}
 import com.uber.h3core.H3Core
 import com.uber.h3core.util.GeoCoord
 import org.apache.spark.sql.types.LongType
 import org.apache.spark.unsafe.types.UTF8String
 import org.locationtech.jts.geom.Geometry
 
 import scala.collection.JavaConverters._
+import scala.collection.mutable
 import scala.util.{Success, Try}
 
 /**
@@ -93,10 +94,9 @@ object H3IndexSystem extends IndexSystem(LongType) with Serializable {
     override def indexToGeometry(index: Long, geometryAPI: GeometryAPI): MosaicGeometry = {
         val boundary = h3.h3ToGeoBoundary(index).asScala
         val extended = boundary ++ List(boundary.head)
-        geometryAPI.geometry(
-          extended.map(p => geometryAPI.fromGeoCoord(Coordinates(p.lat, p.lng))),
-          POLYGON
-        )
+
+        if (crossesNorthPole(index) || crossesSouthPole(index)) makePoleGeometry(boundary, crossesNorthPole(index), geometryAPI)
+        else makeSafeGeometry(extended, geometryAPI)
     }
 
     /**
@@ -198,10 +198,9 @@ object H3IndexSystem extends IndexSystem(LongType) with Serializable {
     override def indexToGeometry(index: String, geometryAPI: GeometryAPI): MosaicGeometry = {
         val boundary = h3.h3ToGeoBoundary(index).asScala
         val extended = boundary ++ List(boundary.head)
-        geometryAPI.geometry(
-          extended.map(p => geometryAPI.fromGeoCoord(Coordinates(p.lat, p.lng))),
-          POLYGON
-        )
+
+        if (crossesNorthPole(index) || crossesSouthPole(index)) makePoleGeometry(boundary, crossesNorthPole(index), geometryAPI)
+        else makeSafeGeometry(extended, geometryAPI)
     }
 
     override def format(id: Long): String = {
@@ -227,4 +226,172 @@ object H3IndexSystem extends IndexSystem(LongType) with Serializable {
 
     override def distance(cellId: Long, cellId2: Long): Long = Try(h3.h3Distance(cellId, cellId2)).map(_.toLong).getOrElse(0)
 
+    // Find all cells that cross the north pole. There always is exactly one cell per resolution.
+    private lazy val northPoleCells = Range.inclusive(0, 15).map(h3.geoToH3(90, 0, _))
+
+    // Find all cells that cross the south pole. There always is exactly one cell per resolution.
+    private lazy val southPoleCells = Range.inclusive(0, 15).map(h3.geoToH3(-90, 0, _))
+
+    private def crossesNorthPole(cell_id: Long): Boolean = northPoleCells contains cell_id
+    private def crossesSouthPole(cell_id: Long): Boolean = southPoleCells contains cell_id
+    private def crossesNorthPole(cell_id: String): Boolean = northPoleCells contains h3.stringToH3(cell_id)
+    private def crossesSouthPole(cell_id: String): Boolean = southPoleCells contains h3.stringToH3(cell_id)
+
+    /**
+      * Check if H3 cell crosses the anti-meridian. This check is not
+      * generalizable for arbitrary polygons.
+      * @param geometry
+      *   H3 Geometry to be checked.
+      * @return
+      *   boolean True if the geometry crosses the anti-meridian, false
+      *   otherwise.
+      */
+    private def crossesAntiMeridian(geometry: MosaicGeometry): Boolean = {
+        val minX = geometry.minMaxCoord("X", "MIN")
+        val maxX = geometry.minMaxCoord("X", "MAX")
+        minX < 0 && maxX >= 0 && ((maxX - minX > 180) || !geometry.isValid)
+    }
+
+    /**
+      * Shift point that falls into the western hemisphere by 360 degrees to the
+      * east.
+      * @param lng
+      *   Longitude of the point to be shifted.
+      * @param lat
+      *   Latitude of the point to be shifted.
+      * @return
+      *   Shifted point.
+      */
+    private def shiftEast(lng: Double, lat: Double): (Double, Double) = {
+        if (lng < 0) (lng + 360.0, lat)
+        else (lng, lat)
+    }
+
+    /**
+      * Shift point that lie east of the eastern hemisphere by 360 degrees to
+      * the west.
+      * @param lng
+      *   Longitude of the point to be shifted.
+      * @param lat
+      *   Latitude of the point to be shifted.
+      * @return
+      *   Shifted point.
+      */
+    private def shiftWest(lng: Double, lat: Double): (Double, Double) = {
+        if (lng >= 180.0) (lng - 360.0, lat)
+        else (lng, lat)
+    }
+
+    /**
+      * @param coordinates
+      *   A collection of [[GeoCoord]]s to be used to create a
+      *   [[MosaicGeometry]].
+      * @param geometryAPI
+      *   An instance of [[GeometryAPI]] to be used to create a
+      *   [[MosaicGeometry]].
+      * @return
+      *   A [[MosaicGeometry]] instance. Generates a polygon using the
+      *   cooridaates for the outer ring in the order they are provided. This
+      *   method will not check for validity of the geometry and may return an
+      *   invalid geometry.
+      */
+    private def makeUnsafeGeometry(coordinates: mutable.Buffer[GeoCoord], geometryAPI: GeometryAPI): MosaicGeometry = {
+        geometryAPI.geometry(
+          coordinates.map(p => geometryAPI.fromGeoCoord(Coordinates(p.lat, p.lng))),
+          POLYGON
+        )
+    }
+
+    /**
+      * A BBox that covers the eastern Hemisphere
+      * @param geometryAPI
+      *   An instance of [[GeometryAPI]] to be used to create the geometry.
+      * @return
+      *   A [[MosaicGeometry]] instance.
+      */
+    private def makeEastBBox(geometryAPI: GeometryAPI): MosaicGeometry =
+        makeUnsafeGeometry(
+          mutable.Buffer(new GeoCoord(-90, 0), new GeoCoord(90, 0), new GeoCoord(90, 180), new GeoCoord(-90, 180), new GeoCoord(-90, 0)),
+          geometryAPI: GeometryAPI
+        )
+
+    /**
+      * A BBox that covers the western Hemisphere shifted by 360 degrees to the
+      * East
+      * @param geometryAPI
+      *   An instance of [[GeometryAPI]] to be used to create the geometry.
+      * @return
+      *   A [[MosaicGeometry]] instance.
+      */
+    private def makeShiftedWestBBox(geometryAPI: GeometryAPI): MosaicGeometry =
+        makeUnsafeGeometry(
+          mutable
+              .Buffer(new GeoCoord(-90, 180), new GeoCoord(90, 180), new GeoCoord(90, 360), new GeoCoord(-90, 360), new GeoCoord(-90, 180)),
+          geometryAPI: GeometryAPI
+        )
+
+    /**
+      * Generate a pole-safe H3 geometry. Pole geometries require two additional
+      * vertices where the pole touches the anti-meridian. This method is not
+      * generalizable for arbitrary polygons.
+      *
+      * @param coordinates
+      *   A collection of [[GeoCoord]]s to be used to create a
+      *   [[MosaicGeometry]].
+      * @param isNorthPole
+      *   Boolean indicating if the pole is the north or south pole.
+      * @param geometryAPI
+      *   An instance of [[GeometryAPI]] to be used to create a
+      *   [[MosaicGeometry]].
+      * @return
+      *   A [[MosaicGeometry]] instance.
+      */
+    private def makePoleGeometry(coordinates: mutable.Buffer[GeoCoord], isNorthPole: Boolean, geometryAPI: GeometryAPI): MosaicGeometry = {
+
+        val lat = if (isNorthPole) 90 else -90
+
+        val coords = coordinates.map(geoCoord => shiftEast(geoCoord.lng, geoCoord.lat)).sortBy(_._1)
+        val lineString = geometryAPI.geometry(
+          coords.map(p => geometryAPI.fromGeoCoord(Coordinates(p._2, p._1))),
+          LINESTRING
+        )
+
+        val westernLine = lineString.intersection(makeEastBBox(geometryAPI))
+        val easternLine = lineString.intersection(makeShiftedWestBBox(geometryAPI)).mapXY(shiftWest)
+
+        val vertices = westernLine.getShellPoints.head ++
+            Seq(geometryAPI.fromGeoCoord(Coordinates(lat, 180)), geometryAPI.fromGeoCoord(Coordinates(lat, -180))) ++
+            easternLine.getShellPoints.head ++ Seq(westernLine.getShellPoints.head.head)
+
+        geometryAPI.geometry(vertices, POLYGON)
+
+    }
+
+    /**
+      * Generate a pole-safe and antimeridian-safe H3 geometry. This method is
+      * not generalizable for arbitrary polygons.
+      *
+      * @param coordinates
+      *   A collection of [[GeoCoord]]s to be used to create a
+      *   [[MosaicGeometry]].
+      * @param geometryAPI
+      *   An instance of [[GeometryAPI]] to be used to create a
+      *   [[MosaicGeometry]].
+      * @return
+      *   A [[MosaicGeometry]] instance.
+      */
+    private def makeSafeGeometry(coordinates: mutable.Buffer[GeoCoord], geometryAPI: GeometryAPI): MosaicGeometry = {
+
+        val unsafeGeometry = makeUnsafeGeometry(coordinates, geometryAPI)
+
+        if (crossesAntiMeridian(unsafeGeometry)) {
+            val shiftedGeometry = unsafeGeometry.mapXY(shiftEast)
+            val westGeom = shiftedGeometry.intersection(makeEastBBox(geometryAPI: GeometryAPI))
+            val eastGeom = shiftedGeometry.intersection(makeShiftedWestBBox(geometryAPI: GeometryAPI)).mapXY(shiftWest)
+            westGeom.union(eastGeom)
+        } else {
+            unsafeGeometry
+        }
+    }
+
 }

src/test/scala/com/databricks/labs/mosaic/core/index/H3IndexSystemTest.scala

@@ -1,15 +1,20 @@
 package com.databricks.labs.mosaic.core.index
 
-import com.databricks.labs.mosaic.core.geometry.api.{ESRI, JTS}
+import com.databricks.labs.mosaic.core.geometry.api.{ESRI, GeometryAPI, JTS}
 import com.databricks.labs.mosaic.core.geometry.{MosaicGeometryESRI, MosaicGeometryJTS}
+import com.databricks.labs.mosaic.core.index.H3IndexSystem.indexToGeometry
 import com.databricks.labs.mosaic.core.types.model.GeometryTypeEnum.{LINESTRING, MULTILINESTRING, MULTIPOINT, MULTIPOLYGON, POINT, POLYGON}
 import com.databricks.labs.mosaic.core.types.model.GeometryTypeEnum
+import com.uber.h3core.H3Core
 import org.apache.spark.sql.types.{BooleanType, LongType, StringType}
 import org.apache.spark.unsafe.types.UTF8String
+import org.scalactic.Tolerance
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers._
 
-class H3IndexSystemTest extends AnyFunSuite {
+import scala.jdk.CollectionConverters.collectionAsScalaIterableConverter
+
+class H3IndexSystemTest extends AnyFunSuite with Tolerance {
 
     test("H3IndexSystem auxiliary methods") {
         val indexRes = H3IndexSystem.pointToIndex(10, 10, 10)
@@ -129,4 +134,32 @@ class H3IndexSystemTest extends AnyFunSuite {
         H3IndexSystem.coerceChipGeometry(geomsWKTs4.map(MosaicGeometryESRI.fromWKT)).isEmpty shouldBe true
     }
 
+    test("indexToGeometry should return valid and correct geometries") {
+        val h3: H3Core = H3Core.newInstance()
+
+        val esriGeomAPI: GeometryAPI = GeometryAPI("ESRI")
+        val jtsGeomAPI: GeometryAPI = GeometryAPI("JTS")
+        val apis = Seq(esriGeomAPI, jtsGeomAPI)
+
+        val baseCells = h3.getRes0Indexes.asScala.toList
+        val lvl1Cells = baseCells.flatMap(h3.h3ToChildren(_, 1).asScala)
+        val testCells = Seq(baseCells, lvl1Cells)
+
+        val baseCellsStr = baseCells.map(h3.h3ToString(_))
+        val lvl1CellsStr = lvl1Cells.map(h3.h3ToString(_))
+        val testCellsStr = Seq(baseCellsStr, lvl1CellsStr)
+
+        apis.foreach(api => {
+            testCells.foreach(cells => {
+                val geoms = cells.map(indexToGeometry(_, api))
+                geoms.foreach(geom => geom.isValid shouldBe true)
+                geoms.foldLeft(0.0)((acc, geom) => acc + geom.getArea) shouldBe ((180.0 * 360.0) +- 0.0001)
+            })
+            testCellsStr.foreach(cells => {
+                val geoms = cells.map(indexToGeometry(_, api))
+                geoms.foreach(geom => geom.isValid shouldBe true)
+                geoms.foldLeft(0.0)((acc, geom) => acc + geom.getArea) shouldBe ((180.0 * 360.0) +- 0.0001)
+            })
+        })
+    }
 }