attempt to fix infinite loop in isochrones generation (valhalla#4547)

.github/workflows/syntax.yml → .github/workflows/lint.yml

@@ -1,4 +1,4 @@
-name: syntax
+name: lint
 on: [pull_request]
 
 jobs:

CHANGELOG.md

@@ -33,6 +33,7 @@
    * FIXED: Config singleton multiple instantiation issue [#4521](https://github.com/valhalla/valhalla/pull/4521)
    * FIXED: Prevent GetShortcut to run into an infinite loop [#4532](https://github.com/valhalla/valhalla/pull/4532)
    * FIXED: fix config generator with thor.costmatrix_allow_second_pass [#4567](https://github.com/valhalla/valhalla/pull/4567)
+   * FIXED: infinite loop or other random corruption in isochrones when retrieving partial shape of an edge [#4547](https://github.com/valhalla/valhalla/pull/4547)
 * **Enhancement**
    * UPDATED: French translations, thanks to @xlqian [#4159](https://github.com/valhalla/valhalla/pull/4159)
    * CHANGED: -j flag for multithreaded executables to override mjolnir.concurrency [#4168](https://github.com/valhalla/valhalla/pull/4168)

src/thor/isochrone.cc

@@ -17,10 +17,18 @@ constexpr float METRIC_PADDING = 10.f;
 template <typename PrecisionT>
 std::vector<GeoPoint<PrecisionT>> OriginEdgeShape(const std::vector<GeoPoint<PrecisionT>>& pts,
                                                   double distance_along) {
+  // just the endpoint really
+  if (distance_along == 0)
+    return {pts.back(), pts.back()};
+
+  // consume shape until we reach the desired distance
   double suffix_len = 0;
   for (auto from = std::next(pts.rbegin()), to = pts.rbegin(); from != pts.rend(); ++from, ++to) {
+    // add whatever this segment of shape contributes to the overall distance
     PrecisionT len = from->Distance(*to);
     suffix_len += len;
+
+    // we have enough distance now, lets find the exact stopping point along the geom
     if (suffix_len >= distance_along) {
       auto interpolated = from->PointAlongSegment(*to, (suffix_len - distance_along) / len);
       std::vector<GeoPoint<PrecisionT>> res(pts.rbegin(), from);
@@ -29,6 +37,8 @@ std::vector<GeoPoint<PrecisionT>> OriginEdgeShape(const std::vector<GeoPoint<Pre
       return res;
     }
   }
+
+  // we got through the whole shape didnt reach the distance, floating point noise probably
   return pts;
 }