From 1561e0c4d259877b04e399b04266b1e8435061bb Mon Sep 17 00:00:00 2001
From: vcoppe <vianney.coppe@gmail.com>
Date: Thu, 20 Jun 2024 18:27:22 +0200
Subject: [PATCH] prevent slope NaNs

---
 gpx/src/gpx.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gpx/src/gpx.ts b/gpx/src/gpx.ts
index 73845aad..cd763c69 100644
--- a/gpx/src/gpx.ts
+++ b/gpx/src/gpx.ts
@@ -688,7 +688,7 @@ export class TrackSegment extends GPXTreeLeaf {
     _computeSlope(): number[] {
         const points = this.trkpt;
 
-        return distanceWindowSmoothingWithDistanceAccumulator(points, 50, (accumulated, start, end) => 100 * (points[end].ele - points[start].ele) / accumulated);
+        return distanceWindowSmoothingWithDistanceAccumulator(points, 50, (accumulated, start, end) => 100 * ((points[end].ele ?? 0) - (points[start].ele ?? 0)) / (accumulated > 0 ? accumulated : 1));
     }
 
     getNumberOfTrackPoints(): number {
@@ -1159,7 +1159,7 @@ function distanceWindowSmoothing(points: ReadonlyArray<Readonly<TrackPoint>>, di
 
     let start = 0, end = 0, accumulated = 0;
     for (var i = 0; i < points.length; i++) {
-        while (start < i && distance(points[start].getCoordinates(), points[i].getCoordinates()) > distanceWindow) {
+        while (start + 1 < i && distance(points[start].getCoordinates(), points[i].getCoordinates()) > distanceWindow) {
             if (remove) {
                 accumulated -= remove(start);
             } else {