Issue 2342 - Handle when start and end are the same point in greatCircle (#2343)

* Handle when start and end are the same point

* Start populating CHANGELOG.md

* See if husky is running yet...

* prettier

* Update handling to match npoints

---------

Co-authored-by: James Beard <[email protected]>

Author: rowanwins

packages/turf-great-circle/README.md

@@ -6,7 +6,8 @@
 
 Calculate great circles routes as [LineString][1] or [MultiLineString][2].
 If the `start` and `end` points span the antimeridian, the resulting feature will
-be split into a `MultiLineString`.
+be split into a `MultiLineString`. If the `start` and `end` positions are the same
+then a `LineString` will be returned with duplicate coordinates the length of the `npoints` option.
 
 ### Parameters
 

packages/turf-great-circle/index.js

@@ -1,10 +1,12 @@
+import { lineString } from "@turf/helpers";
 import { getCoord } from "@turf/invariant";
 import { GreatCircle } from "./lib/arc.js";
 
 /**
  * Calculate great circles routes as {@link LineString} or {@link MultiLineString}.
  * If the `start` and `end` points span the antimeridian, the resulting feature will
- * be split into a `MultiLineString`.
+ * be split into a `MultiLineString`. If the `start` and `end` positions are the same
+ * then a `LineString` will be returned with duplicate coordinates the length of the `npoints` option.
  *
  * @function
  * @param {Coord} start source point feature
@@ -34,8 +36,16 @@ function greatCircle(start, end, options) {
 
   start = getCoord(start);
   end = getCoord(end);
+
   properties = properties || {};
   npoints = npoints || 100;
+
+  if (start[0] === end[0] && start[1] === end[1]) {
+    const arr = Array(npoints);
+    arr.fill([start[0], start[1]]);
+    return lineString(arr, properties);
+  }
+
   offset = offset || 10;
 
   var generator = new GreatCircle(

packages/turf-great-circle/test.ts

@@ -5,7 +5,7 @@ import { fileURLToPath } from "url";
 import { loadJsonFileSync } from "load-json-file";
 import { writeJsonFileSync } from "write-json-file";
 import { truncate } from "@turf/truncate";
-import { featureCollection } from "@turf/helpers";
+import { featureCollection, point, lineString } from "@turf/helpers";
 import { greatCircle } from "./index.js";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
@@ -39,3 +39,23 @@ test("turf-great-circle", (t) => {
   });
   t.end();
 });
+
+test("turf-great-circle with same input and output", (t) => {
+  const start = point([0, 0]);
+  const end = point([0, 0]);
+  const line = greatCircle(start, end, {
+    npoints: 4,
+  });
+
+  t.deepEquals(
+    lineString([
+      [0, 0],
+      [0, 0],
+      [0, 0],
+      [0, 0],
+    ]),
+    line
+  );
+
+  t.end();
+});