add function to convert neo4j native point(s) to WKT format (#409)

Author: Andy2003

src/main/java/org/neo4j/gis/spatial/Constants.java

@@ -69,4 +69,6 @@ public interface Constants {
 	int GTYPE_MULTILINESTRING = 5;
 	int GTYPE_MULTIPOLYGON = 6;
 
+	int SRID_COORDINATES_2D = 4326;
+	int SRID_COORDINATES_3D = 4979;
 }

src/main/java/org/neo4j/gis/spatial/encoders/neo4j/Neo4jCRS.java

@@ -19,6 +19,7 @@
  */
 package org.neo4j.gis.spatial.encoders.neo4j;
 
+import org.neo4j.gis.spatial.Constants;
 import org.neo4j.values.storable.CoordinateReferenceSystem;
 
 public class Neo4jCRS implements org.neo4j.graphdb.spatial.CRS {
@@ -51,7 +52,7 @@ public int dimensions() {
 	public static Neo4jCRS findCRS(String crs) {
 		return switch (crs) {      // name in Neo4j CRS table
 			case "WGS-84", "WGS84(DD)" ->   // name in geotools crs library
-					makeCRS(4326);
+					makeCRS(Constants.SRID_COORDINATES_2D);
 			case "Cartesian" -> makeCRS(7203);
 			default -> throw new IllegalArgumentException("Cypher type system does not support CRS: " + crs);
 		};

src/main/java/org/neo4j/gis/spatial/functions/SpatialFunctions.java

@@ -20,14 +20,22 @@
 
 package org.neo4j.gis.spatial.functions;
 
+import static org.neo4j.gis.spatial.Constants.SRID_COORDINATES_2D;
+import static org.neo4j.gis.spatial.Constants.SRID_COORDINATES_3D;
+
+import java.util.Arrays;
+import java.util.Collection;
+import org.locationtech.jts.geom.Coordinate;
 import org.locationtech.jts.geom.Geometry;
 import org.locationtech.jts.io.ParseException;
 import org.locationtech.jts.io.WKTReader;
+import org.locationtech.jts.io.WKTWriter;
 import org.neo4j.gis.spatial.Layer;
 import org.neo4j.gis.spatial.procedures.SpatialProcedures.GeometryResult;
 import org.neo4j.gis.spatial.utilities.GeoJsonUtils;
 import org.neo4j.gis.spatial.utilities.SpatialApiBase;
 import org.neo4j.graphdb.Node;
+import org.neo4j.graphdb.spatial.Point;
 import org.neo4j.procedure.Description;
 import org.neo4j.procedure.Name;
 import org.neo4j.procedure.UserFunction;
@@ -58,7 +66,6 @@ public Object asGeometry(@Name("geometry") Object geometry) {
 		return toNeo4jGeometry(null, geometry);
 	}
 
-
 	@UserFunction("spatial.wktToGeoJson")
 	@Description("Converts a WKT to GeoJson structure")
 	public Object wktToGeoJson(@Name("wkt") String wkt) throws ParseException {
@@ -69,4 +76,38 @@ public Object wktToGeoJson(@Name("wkt") String wkt) throws ParseException {
 		Geometry geometry = wktReader.read(wkt);
 		return GeoJsonUtils.toGeoJsonStructure(geometry);
 	}
+
+	@UserFunction("spatial.neo4jGeometryToWkt")
+	@Description("Converts a point or point array to WKT")
+	public String nativeToWkt(@Name("data") Object object) {
+		if (object instanceof Point point) {
+			var coordinate = convertToCoordinate(point);
+			return WKTWriter.toPoint(coordinate);
+		}
+		if (object instanceof Point[] points) {
+			var coordinates = Arrays.stream(points).map(SpatialFunctions::convertToCoordinate)
+					.toArray(Coordinate[]::new);
+			return WKTWriter.toLineString(coordinates);
+		}
+		if (object instanceof Collection<?> points) {
+			var coordinates = points.stream()
+					.filter(Point.class::isInstance)
+					.map(Point.class::cast)
+					.map(SpatialFunctions::convertToCoordinate)
+					.toArray(Coordinate[]::new);
+			return WKTWriter.toLineString(coordinates);
+		}
+		throw new IllegalArgumentException("Unsupported type: " + object.getClass());
+	}
+
+	private static Coordinate convertToCoordinate(Point point) {
+		double[] coordinate = point.getCoordinate().getCoordinate();
+		if (point.getCRS().getCode() == SRID_COORDINATES_3D) {
+			return new Coordinate(coordinate[0], coordinate[1], coordinate[2]);
+		} else if (point.getCRS().getCode() == SRID_COORDINATES_2D) {
+			return new Coordinate(coordinate[0], coordinate[1]);
+		} else {
+			throw new IllegalArgumentException("Unsupported CRS: " + point.getCRS().getCode());
+		}
+	}
 }

src/main/java/org/neo4j/gis/spatial/utilities/GeotoolsAdapter.java

@@ -27,6 +27,7 @@
 import org.geotools.api.referencing.crs.CoordinateReferenceSystem;
 import org.geotools.referencing.CRS;
 import org.geotools.referencing.ReferencingFactoryFinder;
+import org.neo4j.gis.spatial.Constants;
 import org.neo4j.gis.spatial.SpatialDatabaseException;
 
 /**
@@ -54,8 +55,8 @@ public static CoordinateReferenceSystem getCRS(String crsText) {
 
 	public static Integer getEPSGCode(CoordinateReferenceSystem crs) {
 		try {
-			// TODO: upgrade geotools to avoid Java11 failures on CRS.lookupEpsgCode
-			return (crs == WGS84) ? Integer.valueOf(4326) : (crs == GENERIC_2D) ? null : CRS.lookupEpsgCode(crs, true);
+			return (crs == WGS84) ? Integer.valueOf(Constants.SRID_COORDINATES_2D)
+					: (crs == GENERIC_2D) ? null : CRS.lookupEpsgCode(crs, true);
 		} catch (FactoryException e) {
 			System.err.println("Failed to lookup CRS: " + e.getMessage());
 			return null;

src/test/java/org/neo4j/gis/spatial/functions/SpatialFunctionsTest.java

@@ -311,4 +311,19 @@ public void testGeometryCollection() {
 			)));
 		}
 	}
+
+	@Test
+	public void testPointToWkt() {
+		Object wkt = executeObject("return spatial.neo4jGeometryToWkt(point({longitude: 1, latitude: 2})) as wkt",
+				"wkt");
+		assertThat(wkt, equalTo("POINT ( 1 2 )"));
+	}
+
+	@Test
+	public void testPointArrayToWkt() {
+		Object wkt = executeObject(
+				"return spatial.neo4jGeometryToWkt([point({longitude: 1, latitude: 2}), point({longitude: 3, latitude: 4}) ]) as wkt",
+				"wkt");
+		assertThat(wkt, equalTo("LINESTRING (1 2, 3 4)"));
+	}
 }