Interpolate coordinates in Mercator space for better accuracy

package.json

@@ -12,6 +12,7 @@
   "author": "",
   "license": "ISC",
   "dependencies": {
+    "@turf/turf": "^5.1.6",
     "axios": "^0.19.2",
     "color": "^3.1.2",
     "csv-parse": "^4.8.3",

src/tam/simulation.js

@@ -1,4 +1,5 @@
 const axios = require('axios');
+const turf = require('@turf/turf');
 const network = require('./network.json');
 
 const server = 'http://localhost:4321';
@@ -189,38 +190,46 @@ const updatePositions = (courses, time) =>
                 const previousNode = segment.points[nextNodeIndex - 1];
                 const nextNode = segment.points[nextNodeIndex];
 
+                const previousPoint = turf.toMercator([
+                    previousNode.lon,
+                    previousNode.lat
+                ]);
+
+                const nextPoint = turf.toMercator([
+                    nextNode.lon,
+                    nextNode.lat
+                ]);
+
                 const curLength = course.traveledDistance
                     - previousNode.distance;
                 const totalLength = nextNode.distance
                     - previousNode.distance;
-                const progression = curLength / totalLength;
+                const t = curLength / totalLength;
 
-                course.position = {
+                course.position = [
-                    lat: progression * nextNode.lat
+                    t * nextPoint[0] + (1 - t) * previousPoint[0],
-                        + (1 - progression) * previousNode.lat,
+                    t * nextPoint[1] + (1 - t) * previousPoint[1],
-                    lon: progression * nextNode.lon
+                ];
-                        + (1 - progression) * previousNode.lon,
-                };
             }
         }
         else
         {
-            const currentStop = network.stops[course.currentStop];
+            const currentNode = network.stops[course.currentStop];
-            course.position = {
+            course.position = turf.toMercator([
-                lat: currentStop.lat,
+                currentNode.lon,
-                lon: currentStop.lon,
+                currentNode.lat
-            };
+            ]);
         }
     }
 };
 
-const run = callback =>
+const start = () =>
 {
     const courses = {};
     let lastFrame = null;
     let lastUpdate = null;
 
-    const loop = () =>
+    const update = () =>
     {
         const now = Date.now();
 
@@ -233,12 +242,9 @@ const run = callback =>
         const time = lastFrame === null ? 0 : now - lastFrame;
         lastFrame = now;
         updatePositions(courses, time);
-
-        callback(courses);
     };
 
-    const interval = setInterval(loop, 24);
+    return {courses, update};
-    return () => clearInterval(interval);
 };
 
-exports.run = run;
+exports.start = start;