RelativeMap: fixed a bug in navigator due to curvature downsampling.

The curvature  is positive at the left turn and negative at the right turn. The previous downsampling strategy didn't consider the right turn scenario.

modules/map/relative_map/tools/navigator.cc

@@ -153,16 +153,16 @@ bool GetNavigationPathFromFile(const std::string& filename,
       auto json_obj = json::parse(line_str);
       current_sampled_s = json_obj["s"];
       current_kappa = json_obj["kappa"];
-      diff_s = current_sampled_s - last_sampled_s;
+      diff_s = std::fabs(current_sampled_s - last_sampled_s);
       bool not_down_sampling =
           FLAGS_navigator_down_sample
               ? diff_s >= kStraightSampleInterval ||
                     (diff_s >= kSmallKappaSampleInterval &&
-                     current_kappa > kSmallKappa) ||
+                     std::fabs(current_kappa) > kSmallKappa) ||
                     (diff_s >= kMiddleKappaSampleInterval &&
-                     current_kappa > kMiddleKappa) ||
+                     std::fabs(current_kappa) > kMiddleKappa) ||
                     (diff_s >= kLargeKappaSampleInterval &&
-                     current_kappa > kLargeKappa)
+                     std::fabs(current_kappa) > kLargeKappa)
               : true;
       if (not_down_sampling) {
         last_sampled_s = current_sampled_s;