refactor(geo): define shared distance contract

src/annotations/annotationEngine.js

@@ -1,5 +1,6 @@
 import { defaultGeospatial } from '../search/defaults.js';
 import * as Cesium from 'cesium';
+import { greatCircleMeters } from '../geoDistance.js';
 import {
   holdContinuousRender,
   releaseContinuousRender,
@@ -1530,16 +1531,7 @@ async function fetchRoute(coordPairs, mode, signal, service) {
 }
 
 function greatCircleM(a, b) {
-  const R = 6371000;
-  const toRad = (deg) => (deg * Math.PI) / 180;
-  const dLat = toRad(b.lat - a.lat);
-  const dLon = toRad(b.lon - a.lon);
-  const la1 = toRad(a.lat);
-  const la2 = toRad(b.lat);
-  const h =
-    Math.sin(dLat / 2) ** 2 +
-    Math.cos(la1) * Math.cos(la2) * Math.sin(dLon / 2) ** 2;
-  return 2 * R * Math.asin(Math.min(1, Math.sqrt(h)));
+  return greatCircleMeters(a, b);
 }
 
 function formatDistance(m) {

src/annotations/drawMode.js

@@ -18,6 +18,8 @@
  * `drawTool.js`.
  */
 
+import { greatCircleMeters } from '../geoDistance.js';
+
 export const DRAW_SHAPES = Object.freeze(['area', 'line', 'pin']);
 export const MIN_VERTICES = Object.freeze({ area: 3, line: 2, pin: 1 });
 /**
@@ -47,14 +49,7 @@ export function createDrawSession(shape = 'area') {
 
 /** Great-circle distance in metres between two {lon, lat} points. */
 export function greatCircleM(a, b) {
-  const R = 6371000;
-  const toRad = (d) => (d * Math.PI) / 180;
-  const dLat = toRad(b.lat - a.lat);
-  const dLon = toRad(b.lon - a.lon);
-  const h =
-    Math.sin(dLat / 2) ** 2 +
-    Math.cos(toRad(a.lat)) * Math.cos(toRad(b.lat)) * Math.sin(dLon / 2) ** 2;
-  return 2 * R * Math.asin(Math.sqrt(Math.min(1, h)));
+  return greatCircleMeters(a, b);
 }
 
 /**