Increase latitude accuracy level

src/api/coords-to-vector-3.ts

@@ -2,14 +2,44 @@ import { MathUtils, Vector3Tuple } from 'three';
 import { Coords } from './coords';
 import { earthRadius } from "../core/earth-radius";
 
+
+const mercatorScaleLookup: { [key: number]: number } = {};
+
+function getMercatorScale(lat: number): number {
+ const index = Math.round(lat * 1000);
+ if (mercatorScaleLookup[index] === undefined) {
+ mercatorScaleLookup[index] = 1 / Math.cos(lat * MathUtils.DEG2RAD);
+ }
+ return mercatorScaleLookup[index];
+}
+
+export function averageMercatorScale(originLat: number, pointLat: number, steps = 10): number {
+ let totalScale = 0;
+ const latStep = (pointLat - originLat) / steps;
+ for (let i = 0; i <= steps; i++) {
+ const lat = originLat + latStep * i;
+ totalScale += getMercatorScale(lat);
+ }
+ return totalScale / (steps + 1);
+}
+
 export function coordsToVector3(point: Coords, origin: Coords): Vector3Tuple {
  const latitudeDiff = (point.latitude - origin.latitude) * MathUtils.DEG2RAD;
  const longitudeDiff = (point.longitude - origin.longitude) * MathUtils.DEG2RAD;
  const altitudeDiff = (point.altitude || 0) - (origin.altitude || 0);
 
  const x = longitudeDiff * earthRadius * Math.cos(origin.latitude * MathUtils.DEG2RAD);
  const y = altitudeDiff;
- const z = -latitudeDiff * earthRadius;
+ const zOld = -latitudeDiff * earthRadius;
+
+ // dynamic step size based on latitude difference. calculate the mercator unit scale at origin
+ // and the scale average along the line to the point for better accuracy far from origin
+ const steps = Math.ceil(Math.abs(point.latitude - origin.latitude)) * 100 + 1;
+ const absOriginLat = Math.abs(origin.latitude); // use abs values for scale calculation (same scale for north and south)
+ const absPointLat = Math.abs(point.latitude);
+ const avgScale = averageMercatorScale(absOriginLat, absPointLat, steps);
+
+ const z = (zOld / getMercatorScale(absOriginLat)) * avgScale;
 
  return [x, y, z] as Vector3Tuple;
-}
+}

src/core/earth-radius.ts

@@ -1 +1 @@
-export const earthRadius = 6378137;
+export const earthRadius = 6371008.8;