planning: fix reference line smoother by adding start point constraint

modules/planning/common/planning_gflags.cc

@@ -35,7 +35,7 @@ DEFINE_bool(publish_estop, false, "publish estop decision in planning");
 DEFINE_bool(enable_trajectory_stitcher, true, "enable stitching trajectory");
 
 DEFINE_double(
-    look_backward_distance, 30,
+    look_backward_distance, 10,
     "look backward this distance when creating reference line from routing");
 
 DEFINE_double(

modules/planning/reference_line/reference_line_smoother.cc

@@ -152,14 +152,12 @@ bool ReferenceLineSmoother::Sampling(const ReferenceLine& raw_reference_line) {
 
 bool ReferenceLineSmoother::ApplyConstraint(
     const ReferenceLine& raw_reference_line) {
-  const double t_length = t_knots_.back() - t_knots_.front();
   uint32_t constraint_num =
       std::max(static_cast<uint32_t>(raw_reference_line.Length() /
                                      smoother_config_.max_constraint_length()),
                3u);
-  double dt = t_length / constraint_num;
   std::vector<double> evaluated_t;
-  common::util::uniform_slice(0.0 + dt, t_length, constraint_num - 1,
+  common::util::uniform_slice(t_knots_.front(), t_knots_.back(), constraint_num,
                               &evaluated_t);
   std::vector<common::PathPoint> path_points;
   if (!ExtractEvaluatedPoints(raw_reference_line, evaluated_t, &path_points)) {

modules/planning/reference_line/reference_line_smoother_test.cc

@@ -71,7 +71,7 @@ TEST_F(ReferenceLineSmootherTest, smooth) {
   ReferenceLine smoothed_reference_line;
   EXPECT_FLOAT_EQ(153.87421, reference_line_->Length());
   EXPECT_TRUE(smoother_.Smooth(*reference_line_, &smoothed_reference_line));
-  EXPECT_FLOAT_EQ(154.66971, smoothed_reference_line.Length());
+  EXPECT_FLOAT_EQ(153.21724, smoothed_reference_line.Length());
 }
 
 }  // namespace planning