Addressed comments from Michel

src/backend/automotive_simulator.cc

@@ -177,8 +177,8 @@ const RoadGeometry* AutomotiveSimulator<T>::SetRoadGeometry(
 }
 
 template <typename T>
-const delphyne::AgentBase<T>& AutomotiveSimulator<T>::GetAgentById(
-    int agent_id) const {
+const delphyne::AgentBase<T>&
+AutomotiveSimulator<T>::GetAgentById(int agent_id) const {
   DELPHYNE_VALIDATE(agents_.count(agent_id) != 0, std::runtime_error,
                     "No agent found with the given ID.");
   return *agents_.at(agent_id);
@@ -348,9 +348,9 @@ void AutomotiveSimulator<T>::Build() {
   // Connects the PoseBundleToSimpleCarState_v input and output.
   builder_->Connect(
       aggregator_->get_output_port(0),
-      pose_bundle_to_simple_car_state_v_->get_pose_bundle_input_port());
+      pose_bundle_to_simple_car_state_v_->get_input_port(0));
   builder_->Connect(
-      pose_bundle_to_simple_car_state_v_->get_simple_car_state_v_output(),
+      pose_bundle_to_simple_car_state_v_->get_output_port(0),
       agents_state_publisher_system->get_input_port(0));
 
   diagram_ = builder_->Build();

src/translations/pose_bundle_to_simple_car_state_v.cc

@@ -8,55 +8,39 @@
 #include <drake/systems/rendering/pose_bundle.h>
 
 #include "delphyne/protobuf/simple_car_state_v.pb.h"
+#include "delphyne/protobuf/simple_car_state.pb.h"
+#include "translations/drake_to_ign.h"
 
 namespace delphyne {
 
-using drake::systems::rendering::PoseBundle;
+const unsigned int kPoseBundleVectorSize{0};
 
-PoseBundleToSimpleCarState_V::PoseBundleToSimpleCarState_V() {
-  const int kPoseBundleVectorSize{0};
-  // Declares input ports.
-  pose_bundle_input_port_index_ =
-      this->DeclareInputPort(drake::systems::kVectorValued,
-                             kPoseBundleVectorSize)
-          .get_index();
-  // Declares output port.
-  output_port_index_ =
-      this->DeclareAbstractOutputPort(
-              &PoseBundleToSimpleCarState_V::CalcSimpleCarState_V)
-          .get_index();
-}
-
-void PoseBundleToSimpleCarState_V::CalcSimpleCarState_V(
-    const drake::systems::Context<double>& context,
-    ignition::msgs::SimpleCarState_V* output) const {
-  // Obtains the input and output.
-  const PoseBundle<double>& pose_bundle =
-      drake::systems::System<double>::EvalAbstractInput(
-          context, pose_bundle_input_port_index_)
-          ->template GetValue<PoseBundle<double>>();
+void PoseBundleToSimpleCarState_V::DoDrakeToIgnTranslation(
+    const drake::systems::rendering::PoseBundle<double>& drake_message,
+    ignition::msgs::SimpleCarState_V* ign_message, int64_t time_ms) const {
 
-  // Clears the current SimpleCarState_V message from its previous content.
-  output->Clear();
+  // Clears state from the previous call.
+  // @see DrakeToIgn::DoDrakeToIgnTranslation
+  ign_message->Clear();
 
-  for (int i = 0; i < pose_bundle.get_num_poses(); ++i) {
+  for (int i = 0; i < drake_message.get_num_poses(); ++i) {
     // Gets the car's pose.
-    const drake::Isometry3<double>& pose = pose_bundle.get_pose(i);
+    const drake::Isometry3<double>& pose = drake_message.get_pose(i);
     // Translates pose from quaternion to euler.
-    const Eigen::Vector3d& euler_rotation =
+    const Eigen::Vector3d euler_rotation =
         pose.rotation().eulerAngles(0, 1, 2);
 
     // Calculates car's velocity.
-    const drake::systems::rendering::FrameVelocity<double>& velocity =
-        pose_bundle.get_velocity(i);
-    const drake::multibody::SpatialVelocity<double>& spatial_velocity =
+    const drake::systems::rendering::FrameVelocity<double> velocity =
+        drake_message.get_velocity(i);
+    const drake::multibody::SpatialVelocity<double> spatial_velocity =
         velocity.get_velocity();
-    const double& velocity_norm =
+    const double velocity_norm =
         static_cast<double>(spatial_velocity.translational().norm());
 
     // Appends a new state to the vector.
-    auto* current_state = output->add_states();
-    current_state->set_name("/agent/" + pose_bundle.get_name(i) + "/state");
+    ignition::msgs::SimpleCarState* current_state = ign_message->add_states();
+    current_state->set_name("/agent/" + drake_message.get_name(i) + "/state");
     current_state->set_x(pose.translation().x());
     current_state->set_y(pose.translation().y());
     current_state->set_heading(euler_rotation(2));

src/translations/pose_bundle_to_simple_car_state_v.h

@@ -2,43 +2,26 @@
 
 #pragma once
 
-#include <drake/systems/framework/leaf_system.h>
+#include <drake/systems/rendering/pose_bundle.h>
+
+#include <ignition/msgs.hh>
 
-#include "delphyne/protobuf/simple_car_state.pb.h"
 #include "delphyne/protobuf/simple_car_state_v.pb.h"
+#include "translations/drake_to_ign.h"
 
 namespace delphyne {
 
 /// @brief A system that takes a PoseBundle and generates an array of
 /// SimpleCarStates (SimpleCarState_V).
-class PoseBundleToSimpleCarState_V : public drake::systems::LeafSystem<double> {
- public:
-  PoseBundleToSimpleCarState_V();
-
-  /// @brief Returns the output port of the system.
-  const drake::systems::OutputPort<double>& get_simple_car_state_v_output()
-      const {
-    return this->get_output_port(output_port_index_);
-  }
-
-  /// @brief Returns the input port descriptor for the pose bundle. This port
-  /// expects a drake::sytems::rendering::PoseBundle<double>.
-  const drake::systems::InputPortDescriptor<double>&
-  get_pose_bundle_input_port() const {
-    return get_input_port(pose_bundle_input_port_index_);
-  }
-
+class PoseBundleToSimpleCarState_V
+    : public DrakeToIgn<drake::systems::rendering::PoseBundle<double>,
+                        ignition::msgs::SimpleCarState_V> {
  protected:
-  /// @brief Calculates the SimpleCarState_V message based on the given context.
-  void CalcSimpleCarState_V(const drake::systems::Context<double>& context,
-                            ignition::msgs::SimpleCarState_V* output) const;
-
- private:
-  // @brief The pose bundle input port index assigned by the system.
-  int pose_bundle_input_port_index_{};
-
-  // @brief The abstract output port index assigned by the system.
-  int output_port_index_{};
+  // @brief @see DrakeToIgn::DoDrakeToIgnTranslation.
+  void DoDrakeToIgnTranslation(
+      const drake::systems::rendering::PoseBundle<double>& drake_message,
+      ignition::msgs::SimpleCarState_V* ign_message,
+      int64_t time_ms) const override;
 };
 
 }  // namespace delphyne

test/regression/cpp/automotive_simulator_test.cc

@@ -225,6 +225,8 @@ TEST_F(AutomotiveSimulatorTest, TestPriusSimpleCar) {
       kStateMessagesCount, kTimeoutMs,
       [this, &simulator]() { simulator->StepBy(kSmallTimeStep); }));
 
+  EXPECT_TRUE(ign_monitor.get_last_message().states_size() > 0);
+
   ignition::msgs::SimpleCarState state_message =
       ign_monitor.get_last_message().states(0);
   EXPECT_LT(state_message.x(), 0.1);
@@ -264,12 +266,15 @@ TEST_F(AutomotiveSimulatorTest, TestPriusSimpleCarInitialState) {
       kStateMessagesCount, kTimeoutMs,
       [this, &simulator]() { simulator->StepBy(kSmallTimeStep); }));
 
+
+  EXPECT_TRUE(ign_monitor.get_last_message().states_size() > 0);
+
   const ignition::msgs::SimpleCarState state_message =
       ign_monitor.get_last_message().states(0);
 
-  // A very minimal loss of accuracy is produced during the conversion from the
-  // PoseBundle to the SimpleCarState. Hence, a small tolerance is allowed when
-  // comparing the values from the SimpleCarState with the expected values.
+  // Computations of SimpleCarState from a PoseBundle incur minimal numerical
+  // precision loss. Hence, a small tolerance is allowed when comparing the
+  // values from the SimpleCarState with the expected values.
   const double kAccuracy = 1e-15;
 
   EXPECT_EQ(state_message.x(), kX);