solar_system.cc

#include "drake/examples/scene_graph/solar_system.h"

#include <memory>
#include <string>
#include <utility>
#include <vector>

#include "drake/common/find_resource.h"
#include "drake/geometry/frame_kinematics_vector.h"
#include "drake/geometry/geometry_frame.h"
#include "drake/geometry/geometry_instance.h"
#include "drake/geometry/geometry_roles.h"
#include "drake/systems/framework/continuous_state.h"
#include "drake/systems/framework/discrete_values.h"

namespace drake {
namespace examples {
namespace solar_system {

using Eigen::AngleAxisd;
using Eigen::Translation3d;
using Eigen::Vector3d;
using Eigen::Vector4d;
using geometry::Box;
using geometry::Capsule;
using geometry::Convex;
using geometry::Cylinder;
using geometry::FrameId;
using geometry::FramePoseVector;
using geometry::GeometryFrame;
using geometry::GeometryId;
using geometry::GeometryInstance;
using geometry::IllustrationProperties;
using geometry::SceneGraph;
using geometry::Mesh;
using geometry::SourceId;
using geometry::Sphere;
using math::RigidTransformd;
using systems::BasicVector;
using systems::Context;
using systems::ContinuousState;
using systems::DiscreteValues;
using std::make_unique;
using std::unique_ptr;

template <typename Shape, typename... ShapeArgs>
unique_ptr<GeometryInstance> MakeShape(const RigidTransformd& pose,
                                       const std::string& name,
                                       const Vector4d& diffuse,
                                       ShapeArgs&&... args) {
  auto instance = make_unique<GeometryInstance>(
      pose, make_unique<Shape>(std::forward<ShapeArgs>(args)...), name);
  IllustrationProperties properties;
  properties.AddProperty("phong", "diffuse", diffuse);
  instance->set_illustration_properties(properties);
  return instance;
}

template <typename T>
SolarSystem<T>::SolarSystem(SceneGraph<T>* scene_graph) {
  DRAKE_DEMAND(scene_graph);
  source_id_ = scene_graph->RegisterSource("solar_system");

  this->DeclareContinuousState(kBodyCount /* num_q */, kBodyCount /* num_v */,
                               0 /* num_z */);

  AllocateGeometry(scene_graph);

  // Now that frames have been registered, allocate the output port.
  geometry_pose_port_ =
      this->DeclareAbstractOutputPort(&SolarSystem::CalcFramePoseOutput,
                                      {this->configuration_ticket()})
          .get_index();
}

template <typename T>
const systems::OutputPort<T>& SolarSystem<T>::get_geometry_pose_output_port()
    const {
  return systems::System<T>::get_output_port(geometry_pose_port_);
}

template <typename T>
void SolarSystem<T>::SetDefaultState(const systems::Context<T>&,
                                     systems::State<T>* state) const {
  DRAKE_DEMAND(state != nullptr);
  ContinuousState<T>& xc = state->get_mutable_continuous_state();
  VectorX<T> initial_state;
  initial_state.resize(kBodyCount * 2);
  // clang-format off
  initial_state << 0,               // Earth initial position
                   M_PI / 2,        // moon initial position
                    7 * M_PI / 6,   // convexsat initial position
                   11 * M_PI / 6,   // boxsat initial position
                   M_PI / 6,        // capsulesat initial position
                   M_PI / 2,        // Mars initial position
                   0,               // phobos initial position
                   2 * M_PI / 5,    // Earth revolution lasts 5 seconds.
                   2 * M_PI,        // moon revolution lasts 1 second.
                   2 * M_PI,        // convexsat revolution lasts 1 second.
                   2 * M_PI,        // boxsat revolution lasts 1 second.
                   2 * M_PI,        // capsulesat revolution lasts 1 second.
                   2 * M_PI / 6,    // Mars revolution lasts 6 seconds.
                   2 * M_PI / 1.1;  // phobos revolution lasts 1.1 seconds.
  // clang-format on
  DRAKE_DEMAND(xc.size() == initial_state.size());
  xc.SetFromVector(initial_state);
  DiscreteValues<T>& xd = state->get_mutable_discrete_state();
  for (int i = 0; i < xd.num_groups(); i++) {
    BasicVector<T>& s = xd.get_mutable_vector(i);
    s.SetFromVector(VectorX<T>::Zero(s.size()));
  }
}

// Registers geometry to form an L-shaped arm onto the given frame. The arm is
// defined as shown below:
//
//                        ◯          ← z = height
//   x = 0                │
//   ↓                    │ height
//   ─────────────────────┘          ← z = 0
//                        ↑
//                        x = length
//
// The arm's horizontal length is oriented with the x-axis. The vertical length
// is oriented with the z-axis. The origin of the arm is defined at the local
// origin, and the top of the arm is positioned at the given height.
template <class ParentId>
void MakeArm(SourceId source_id, ParentId parent_id, double length,
             double height, double radius, const Vector4d& material,
             SceneGraph<double>* scene_graph) {
  // tilt it horizontally
  const math::RigidTransform<double> arm_pose(
      AngleAxisd(M_PI / 2, Vector3d::UnitY()), Vector3d(length / 2, 0, 0));
  scene_graph->RegisterGeometry(
      source_id, parent_id,
      MakeShape<Cylinder>(arm_pose, "HorzArm", material, radius, length));

  const math::RigidTransform<double> post_pose(Vector3d(length, 0, height / 2));
  scene_graph->RegisterGeometry(
      source_id, parent_id,
      MakeShape<Cylinder>(post_pose, "VertArm", material, radius, height));
}

template <typename T>
void SolarSystem<T>::AllocateGeometry(SceneGraph<T>* scene_graph) {
  body_ids_.reserve(kBodyCount);
  body_offset_.reserve(kBodyCount);
  axes_.reserve(kBodyCount);

  Vector4d post_material(0.3, 0.15, 0.05, 1);
  const double orrery_bottom = -1.5;
  const double pipe_radius = 0.05;

  // Allocate the sun.
  // NOTE: we don't store the id of the sun geometry because we have no need
  // for subsequent access (the same is also true for dynamic geometries).
  scene_graph->RegisterAnchoredGeometry(
      source_id_, MakeShape<Sphere>(RigidTransformd::Identity(), "Sun",
                                    Vector4d(1, 1, 0, 1), 1.0 /* radius */));

  // The fixed post on which Sun sits and around which all planets rotate.
  const double post_height = 1;
  const RigidTransformd post_pose(
      Translation3d{0, 0, orrery_bottom + post_height / 2});
  scene_graph->RegisterAnchoredGeometry(
      source_id_, MakeShape<Cylinder>(post_pose, "Post", post_material,
                                      pipe_radius, post_height));

  // Allocate the "celestial bodies": two planets orbiting on different planes,
  // each with a moon.

  // For the full description of the frame labels, see solar_system.h.

  // Earth's orbital frame Oe lies directly *below* the sun (to account for the
  // orrery arm).
  const double kEarthBottom = orrery_bottom + 0.25;
  const RigidTransformd X_SOe{Translation3d{0, 0, kEarthBottom}};
  FrameId planet_id =
      scene_graph->RegisterFrame(source_id_, GeometryFrame("EarthOrbit"));
  body_ids_.push_back(planet_id);
  body_offset_.push_back(X_SOe);
  axes_.push_back(Vector3d::UnitZ());

  // The geometry is rigidly affixed to Earth's orbital frame so that it moves
  // in a circular path.
  const double kEarthOrbitRadius = 3.0;
  RigidTransformd X_OeE{Translation3d{kEarthOrbitRadius, 0, -kEarthBottom}};
  scene_graph->RegisterGeometry(
      source_id_, planet_id,
      MakeShape<Sphere>(X_OeE, "Earth", Vector4d(0, 0, 1, 1), 0.25));
  // Earth's orrery arm.
  MakeArm(source_id_, planet_id, kEarthOrbitRadius, -kEarthBottom, pipe_radius,
          post_material, scene_graph);

  // Luna's orbital frame Ol is at the center of Earth's geometry (E).
  // So, X_OeOl = X_OeE.
  const RigidTransformd& X_OeOl = X_OeE;
  FrameId luna_id = scene_graph->RegisterFrame(
      source_id_, planet_id, GeometryFrame("LunaOrbit"));
  body_ids_.push_back(luna_id);
  body_offset_.push_back(X_OeOl);
  const Vector3d luna_axis_Oe{1, 1, 1};
  axes_.push_back(luna_axis_Oe.normalized());

  // The geometry is rigidly affixed to Luna's orbital frame so that it moves
  // in a circular path.
  const double kLunaOrbitRadius = 0.35;
  // Pick a position at kLunaOrbitRadius distance from the Earth's origin on
  // the plane _perpendicular_ to the moon's normal (<1, 1, 1>).
  // luna_position.dot(luna_axis_Oe) will be zero.
  Vector3d luna_position =
      Vector3d(-1, 0.5, 0.5).normalized() * kLunaOrbitRadius;
  RigidTransformd X_OlL{Translation3d{luna_position}};
  scene_graph->RegisterGeometry(
      source_id_, luna_id,
      MakeShape<Sphere>(X_OlL, "Luna", Vector4d(0.5, 0.5, 0.35, 1.0), 0.075));

  // Convex satellite orbits Earth in the same revolution as Luna but with
  // different initial position. See SetDefaultState().
  FrameId convexsat_id = scene_graph->RegisterFrame(
      source_id_, planet_id, GeometryFrame("ConvexSatelliteOrbit"));
  body_ids_.push_back(convexsat_id);
  body_offset_.push_back(X_OeOl);
  axes_.push_back(luna_axis_Oe.normalized());

  std::string convexsat_absolute_path =
      FindResourceOrThrow("drake/examples/scene_graph/cuboctahedron.obj");
  scene_graph->RegisterGeometry(
      source_id_, convexsat_id,
      MakeShape<Convex>(X_OlL, "ConvexSatellite", Vector4d(1, 1, 0, 1),
                        convexsat_absolute_path, 0.075));

  // Box satellite orbits Earth in the same revolution as Luna but with
  // different initial position. See SetDefaultState().
  FrameId boxsat_id = scene_graph->RegisterFrame(
      source_id_, planet_id, GeometryFrame("BoxSatelliteOrbit"));
  body_ids_.push_back(boxsat_id);
  body_offset_.push_back(X_OeOl);
  axes_.push_back(luna_axis_Oe.normalized());

  scene_graph->RegisterGeometry(
      source_id_, boxsat_id,
      MakeShape<Box>(X_OlL, "BoxSatellite", Vector4d(1, 0, 1, 1), 0.15, 0.15,
                     0.15));

  // Capsule satellite orbits Earth in the same revolution as Luna but with
  // different initial position. See SetDefaultState().
  FrameId capsulesat_id = scene_graph->RegisterFrame(
      source_id_, planet_id, GeometryFrame("CapsuleSatelliteOrbit"));
  body_ids_.push_back(capsulesat_id);
  body_offset_.push_back(X_OeOl);
  axes_.push_back(luna_axis_Oe.normalized());

  scene_graph->RegisterGeometry(
      source_id_, capsulesat_id,
      MakeShape<Capsule>(X_OlL, "CapsuleSatellite", Vector4d(0, 1, 1, 1), 0.075,
                         0.2));

  // Mars's orbital frame Om lies directly *below* the sun (to account for the
  // orrery arm).
  RigidTransformd X_SOm{Translation3d{0, 0, orrery_bottom}};
  planet_id =
      scene_graph->RegisterFrame(source_id_, GeometryFrame("MarsOrbit"));
  body_ids_.push_back(planet_id);
  body_offset_.push_back(X_SOm);
  Vector3d mars_axis_S{0, 0.1, 1};
  axes_.push_back(mars_axis_S.normalized());

  // The geometry is rigidly affixed to Mars's orbital frame so that it moves
  // in a circular path.
  const double kMarsOrbitRadius = 5.0;
  const double kMarsSize = 0.24;
  RigidTransformd X_OmM{
      Translation3d{kMarsOrbitRadius, 0, -orrery_bottom}};
  GeometryId mars_geometry_id = scene_graph->RegisterGeometry(
      source_id_, planet_id,
      MakeShape<Sphere>(X_OmM, "Mars", Vector4d(0.9, 0.1, 0, 1), kMarsSize));

  std::string rings_absolute_path =
      FindResourceOrThrow("drake/examples/scene_graph/planet_rings.obj");
  Vector3d axis = Vector3d(1, 1, 1).normalized();
  RigidTransformd X_MR(AngleAxisd(M_PI / 3, axis), Vector3d{0, 0, 0});
  scene_graph->RegisterGeometry(
      source_id_, mars_geometry_id,
      MakeShape<Mesh>(X_MR, "MarsRings", Vector4d(0.45, 0.9, 0, 1),
                      rings_absolute_path, kMarsSize));

  // Mars's orrery arm.
  MakeArm(source_id_, planet_id, kMarsOrbitRadius, -orrery_bottom, pipe_radius,
          post_material, scene_graph);

  // Phobos's orbital frame Op is at the center of Mars (M).
  // So, X_OmOp = X_OmM. The normal of the plane is negated so it orbits in the
  // opposite direction.
  const RigidTransformd& X_OmOp = X_OmM;
  FrameId phobos_id = scene_graph->RegisterFrame(source_id_, planet_id,
                                                 GeometryFrame("PhobosOrbit"));
  body_ids_.push_back(phobos_id);
  body_offset_.push_back(X_OmOp);
  mars_axis_S << 0, 0, -1;
  axes_.push_back(mars_axis_S.normalized());

  // The geometry is displaced from the Phobos's frame so that it orbits.
  const double kPhobosOrbitRadius = 0.34;
  const RigidTransformd X_OpP{Translation3d{kPhobosOrbitRadius, 0, 0}};
  scene_graph->RegisterGeometry(
      source_id_, phobos_id,
      MakeShape<Sphere>(X_OpP, "Phobos", Vector4d(0.65, 0.6, 0.8, 1), 0.06));

  DRAKE_DEMAND(static_cast<int>(body_ids_.size()) == kBodyCount);
}

template <typename T>
void SolarSystem<T>::CalcFramePoseOutput(const Context<T>& context,
                                         FramePoseVector<T>* poses) const {
  const BasicVector<T>& state = get_state(context);
  poses->clear();
  for (int i = 0; i < kBodyCount; ++i) {
    math::RigidTransform<T> pose(body_offset_[i]);
    // Frames only revolve around their origin; it is only necessary to set the
    // rotation value.
    T rotation{state[i]};
    pose.set_rotation(AngleAxis<T>(rotation, axes_[i]));
    poses->set_value(body_ids_[i], pose);
  }
}

template <typename T>
void SolarSystem<T>::DoCalcTimeDerivatives(
    const MyContext& context, MyContinuousState* derivatives) const {
  const BasicVector<T>& state = get_state(context);
  BasicVector<T>& derivative_vector = get_mutable_state(derivatives);
  derivative_vector.SetZero();
  derivative_vector.get_mutable_value().head(kBodyCount) =
      state.get_value().tail(kBodyCount);
}

template class SolarSystem<double>;

}  // namespace solar_system
}  // namespace examples
}  // namespace drake