consolidation of various example repos/gists

typescript/geo/radiusToPolygon/helpers.ts

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+import { Point } from "./point";
+
+/**
+ * Converts an angle in radians to an angle in degrees by multiplying with 180 and dividing by 180
+ * @param angleInRadians
+ */
+export const radiansToDegrees = (angleInRadians: number) => {
+  return (angleInRadians * 180) / Math.PI;
+};
+
+/**
+ * Convert an angle in degrees to an angle in radians by multiplying by PI and dividing the result by 180
+ * https://www.mathwarehouse.com/trigonometry/radians/convert-degee-to-radians.php
+ * @param angleInDegrees
+ */
+export const degreesToRadians = (angleInDegrees: number) => {
+  return (angleInDegrees * Math.PI) / 180;
+};
+
+/**
+ * Convert a point object to an array of longitude,latitude
+ * @param point
+ */
+export const pointToLongLatArray = (point: Point) => {
+  return [point.longitude, point.latitude];
+};
+
+/**
+ * Get a new point given a point, distance and bearing
+ * https://www.igismap.com/formula-to-find-bearing-or-heading-angle-between-two-points-latitude-longitude/#:~:text=Here%20is%20the%20formula%20to,%E2%80%93%20sin%20la1%20*%20sin%20la2)
+ */
+export const getRelativePointByDistance = (
+  point: Point,
+  distance: number,
+  bearing: number
+): Point => {
+  const latitude = Math.asin(
+    Math.sin(point.latitude) * Math.cos(distance) +
+      Math.cos(point.latitude) * Math.sin(distance) * Math.cos(bearing)
+  );
+  const longitude =
+    point.longitude +
+    Math.atan2(
+      Math.sin(bearing) * Math.sin(distance) * Math.cos(point.latitude),
+      Math.cos(distance) - Math.sin(point.latitude) * Math.sin(latitude)
+    );
+
+  return {
+    latitude: radiansToDegrees(latitude),
+    longitude: radiansToDegrees(longitude),
+  };
+};

typescript/geo/radiusToPolygon/index.ts

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+import {
+  degreesToRadians,
+  getRelativePointByDistance,
+  pointToLongLatArray,
+} from "./helpers";
+import { Point } from "./point";
+
+/**
+ *
+ */
+const options = {
+  /**
+   * IERS Equatorial Radius of the earth
+   * https://en.wikipedia.org/wiki/Earth_ellipsoid
+   */
+  equatorialRadiusInMeters: 6378136.6,
+
+  /**
+   * Number of edges to create in the polygon
+   * Use 360 to get a true circle
+   */
+  numberOfEdges: 64,
+};
+
+const input = {
+  center: { latitude: 51.7543453, longitude: 5.5526647 } as Point,
+  radius: 2000,
+};
+
+const coordinates = [];
+for (var i = 0; i < options.numberOfEdges; ++i) {
+  const newPoint = getRelativePointByDistance(
+    {
+      latitude: degreesToRadians(input.center.latitude),
+      longitude: degreesToRadians(input.center.longitude),
+    },
+    input.radius / options.equatorialRadiusInMeters,
+    // find bearing https://www.igismap.com/formula-to-find-bearing-or-heading-angle-between-two-points-latitude-longitude/
+    (2 * Math.PI * -i) / options.numberOfEdges
+  );
+  coordinates.push(pointToLongLatArray(newPoint));
+}
+// make sure the circle is closed by pushing a copy of the first element
+coordinates.push(coordinates[0]);
+
+console.log(
+  JSON.stringify(
+    {
+      type: "Polygon",
+      coordinates: [coordinates],
+    },
+    null,
+    2
+  )
+);

typescript/geo/radiusToPolygon/point.ts

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+export interface Point {
+  latitude: number;
+  longitude: number;
+}