Flatten simple geometry collections (#42)

* Add failing test for GeometryCollection simplifcation

* Simplify GeometryCollections containing a single Polygon

GeoJSONLint complains about these types of features:

> GeometryCollection with a single geometry should be avoided in favor
> of single part or a single object of multi-part type

This simultaneously expands (`GeometryCollection | Polygon`) and narrows
(`GeometryCollection<Polygon | LineString>`) the type of GeoJSON
features created from isolines.

* Update CHANGELOG

* 1.2.0

CHANGELOG.md

@@ -1,4 +1,13 @@
-# 1.1.0
+# Changes
+
+## 1.2.0
+
+### ✨ Features and improvements
+
+- Generate individual Polygons rather than GeometryCollections when isoline features contain single
+  geometries
+
+## 1.1.0
 
 ### ✨ Features and improvements
 

README.md

@@ -266,11 +266,13 @@ const featureCollections = calculateRoutesResponseToFeatureCollections(response)
 
 ### calculateIsolinesResponseToFeatureCollection
 
-This converts a CalculateIsolineResponse from the standalone Routes SDK to a GeoJSON FeatureCollection which contains one Feature for each isoline
-in the response. Isolines can contain both polygons for isoline regions and lines for connectors between regions
-(such as ferry travel), so each Feature is a GeometryCollection that can contain a mix of Polygons and LineStrings.
-The `flattenProperties` option will flatten the nested response data into a flat properties list.
-This option is enabled by default, as it makes the data easier to use from within MapLibre expressions.
+This converts a CalculateIsolineResponse from the standalone Routes SDK to a GeoJSON
+FeatureCollection which contains one Feature for each isoline in the response. Isolines can contain
+both polygons for isoline regions and lines for connectors between regions (such as ferry travel),
+so each Feature contains either a GeometryCollection with a mix of Polygons and LineStrings or a
+single Polygon. The `flattenProperties` option will flatten the nested response data into a flat
+properties list. This option is enabled by default, as it makes the data easier to use from within
+MapLibre expressions.
 
 Any feature that is missing its geometry in the response or has invalid geometry will throw an Error().
 

package.json

@@ -2,7 +2,7 @@
   "name": "@aws/amazon-location-utilities-datatypes",
   "description": "Amazon Location Utilities - Data Types for JavaScript",
   "license": "Apache-2.0",
-  "version": "1.1.0",
+  "version": "1.2.0",
   "keywords": [],
   "author": {
     "name": "Amazon Web Services",

src/to-geojson/georoutes-converter.test.ts

@@ -1710,6 +1710,59 @@ describe("calculateIsolinesResponseToFeatureCollection", () => {
 
     expect(calculateIsolinesResponseToFeatureCollection(input, { flattenProperties: true })).toEqual(expectedResult);
   });
+
+  it("should return a Polygon (not a GeometryCollection) if no LineString is produced", () => {
+    const input: CalculateIsolinesResponse = {
+      IsolineGeometryFormat: "FlexiblePolyline",
+      PricingBucket: "bucket",
+      Isolines: [
+        {
+          Connections: [],
+          Geometries: [
+            {
+              PolylinePolygon: [
+                encodeFromLngLatArray([
+                  [0, 0],
+                  [10, 0],
+                  [10, 10],
+                  [0, 10],
+                  [0, 0],
+                ]),
+              ],
+            },
+          ],
+          TimeThreshold: 1000,
+        },
+      ],
+    };
+
+    const expectedResult: FeatureCollection = {
+      type: "FeatureCollection",
+      features: [
+        {
+          type: "Feature",
+          id: 0,
+          geometry: {
+            type: "Polygon",
+            coordinates: [
+              [
+                [0, 0],
+                [10, 0],
+                [10, 10],
+                [0, 10],
+                [0, 0],
+              ],
+            ],
+          },
+          properties: {
+            TimeThreshold: 1000,
+          },
+        },
+      ],
+    };
+
+    expect(calculateIsolinesResponseToFeatureCollection(input, { flattenProperties: false })).toEqual(expectedResult);
+  });
 });
 
 describe("optimizeWaypointsResponseToFeatureCollection", () => {

src/to-geojson/georoutes-converter.ts

@@ -343,7 +343,8 @@ const defaultCalculateIsolinesResponseOptions = defaultBaseGeoRoutesOptions;
 /**
  * This converts a CalculateIsolineResponse to a GeoJSON FeatureCollection which contains one Feature for each isoline
  * in the response. Isolines can contain both polygons for isoline regions and lines for connectors between regions
- * (such as ferry travel), so each Feature is a GeometryCollection that can contain a mix of Polygons and LineStrings.
+ * (such as ferry travel), so each Feature contains either a GeometryCollection with a mix of Polygons and LineStrings
+ * or a single Polygon.
  *
  * Any feature that is missing its geometry in the response or has invalid geometry will throw an Error.
  *
@@ -405,11 +406,11 @@ const defaultCalculateIsolinesResponseOptions = defaultBaseGeoRoutesOptions;
 export function calculateIsolinesResponseToFeatureCollection(
   isolinesResponse: CalculateIsolinesResponse,
   options?: CalculateIsolinesResponseOptions,
-): FeatureCollection<GeometryCollection> {
+): FeatureCollection<GeometryCollection<Polygon | LineString> | Polygon> {
   // Set any options that weren't passed in to the default values.
   options = { ...defaultCalculateIsolinesResponseOptions, ...options };
 
-  const isolines: FeatureCollection<GeometryCollection> = {
+  const isolines: FeatureCollection<GeometryCollection<Polygon | LineString> | Polygon> = {
     type: "FeatureCollection",
     features: [],
   };
@@ -420,7 +421,7 @@ export function calculateIsolinesResponseToFeatureCollection(
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     const { Geometries, Connections, ...properties } = isoline;
 
-    const feature: Feature<GeometryCollection> = {
+    const feature: Feature<GeometryCollection<Polygon | LineString>> = {
       type: "Feature",
       id: isolines.features.length,
       properties: options.flattenProperties ? flattenProperties(properties, "") : properties,
@@ -448,7 +449,20 @@ export function calculateIsolinesResponseToFeatureCollection(
 
     // As long as this feature has at least one polygon or line, add it to the result set.
     if (feature.geometry.geometries.length > 0) {
-      isolines.features.push(feature);
+      if (feature.geometry.geometries.length === 1 && feature.geometry.geometries[0].type === "Polygon") {
+        // GeometryCollections containing single geometries trigger GeoJSONLint warnings:
+        //     GeometryCollection with a single geometry should be avoided in favor of single part
+        //     or a single object of multi-part type
+        // in practice, the geometry type for single-geometry isolines is Polygon; LineStrings are
+        // supplemental and appear when multiple polygons are present, representing the connection
+        // between those areas
+        isolines.features.push({
+          ...feature,
+          geometry: feature.geometry.geometries[0],
+        });
+      } else {
+        isolines.features.push(feature);
+      }
     }
   }