improve docs (#40)

* fix rules' flags

* add basic VIC controller doc

(cherry picked from commit 3bd70c6)

Author: tpoignonec

README.md

@@ -8,7 +8,7 @@ Set of cartesian controllers for ros2_control
 
 
 
-### Installation of the package
+# Installation of the package
 
 ```bash
 # Create a ros2 workspace with a source dir inside
@@ -40,7 +40,89 @@ colcon build --cmake-args -DCMAKE_BUILD_TYPE=Release --symlink-install
 source install/setup.bash
 ```
 
+## Code organization
+
+### Overview
+
+The following diagram describes the relation between packages:
+![UML class diagram](./cartesian_vic_controller/doc/UML_cartesian_vic_controllers.drawio.png)
+Note that this class diagram is NOT comprehensive and only features the main relations.
+
+The main core ROS dependencies are `ros_control`, `generate_parameters_library`, `kinematics__interface`.
+The VIC controller makes use of the [dynamics_interface](https://github.com/tpoignonec/dynamics_interface) package for dynamic model access (based on kinematics_interface).
+
+Additionally, the servo-based VIC implementation naturally requires the `moveit2` stack, including the latest `moveit_servo` package.
+
+__Packages:__
+- `cartesian_control_msgs`: definition of main messages for VIC controllers state and references. Additionally, messages representing the Cartesian state of a manipulator robot are defined here.
+- `cartesian_state_broadcaster`: simple controller to broadcast the cartesian state (pose + velocity + force).
+- `cartesian_vic_controller`: main repos, see following section.
+- `cartesian_vic_teleop_controller`: extension of `cartesian_vic_controller` to bilateral VIC-based teleoperation.
+- `cartesian_vic_servo`: alternative implementation for VIC (admittance controller only) using MoveIt2 servo as underlying Cartesian velocity controller.
+
+### Cartesian VIC controller
+
+This is the main package that defines the control logic and the default VIC controller (based on ros-control).
+As visible in the diagram class diagram, the main control logic (see details in [cartesian_vic_controller/README.md](./cartesian_vic_controller/README.md)) is provided by the `CartesianVicRule` class.
+
+```mermaid
+classDiagram
+    note for VicRule "Pluginlib plugin"
+    CartesianVicRule <|-- VicRuleImpl
+    class CartesianVicRule{
+        + init()*
+        + configure()*
+        + update()
+        + reset()*
+        + init_reference_frame_trajectory()
+        + update_compliant_frame_trajectory()
+        + controller_state_to_msg()
+        # compute_controls()*
+    }
+    class VicRuleImpl{
+        + init()*
+        + configure()*
+        + reset()*
+        # compute_controls()*
+    }
+```
+
+The base class `CartesianVicRule` provide the logic for robot state processing and packaging (see `VicInputData` class).
+It is also responsible for managing robot kinematic / dynamics  and measurement filtering.
+The `update()` function inernally calls the `compute_controls()`, a pure virtual function that has to be provided by actual VIC implementations.
+
+Each rule inherits from `CartesianVicRule` and provide an implementation of `compute_controls`, whose signature is as follows:
+
+```cpp
+bool CartesianVicRule::compute_controls(
+    double dt /*period in seconds*/,
+    const VicInputData & vic_input_data,
+    VicCommandData & vic_command_data);
+```
+
+The implementation compute VIC controls from the `VicInputData` and returns commands in the form of a `VicCommandData` object. For instance, if the implementation is based on position control (e.g., admittance control) the following is valid:
+
+```cpp
+// Set position reference
+vic_command_data.joint_command_position = <...>;
+
+// Set flags for available commands
+// - Cartesian space
+vic_command_data.has_twist_command = false;
+// - joint space
+vic_command_data.has_position_command = true;
+vic_command_data.has_velocity_command = false;
+vic_command_data.has_acceleration_command = false;
+vic_command_data.has_effort_command = false;
+```
+
+__Provided VIC rule implementations:__
+
+- `VanillaCartesianAdmittanceRule`: a basic admittance control law that returns position and velocity (__recommended!__) commands.
+- `VanillaCartesianImpedanceRule`: a basic impedance control law that returns torque (i.e., `EFFORT`) commands.
+- `TwistCmdCartesianAdmittanceRule`: Same as `VanillaCartesianAdmittanceRule`, but the inverse kinematics is not handled.
+Note: this plugin is not compatible with the nominal controller, it is designed for `cartesian_vic_servo`.
 
-### Examples
+## Examples
 
 See the repos [ICube-Robotics/cartesian_controllers_ros2_examples](https://github.com/ICube-Robotics/cartesian_controllers_ros2_examples).

cartesian_vic_controller/doc/UML_cartesian_vic_controllers.drawio.png

@@ -423,6 +423,7 @@ bool VanillaCartesianAdmittanceRule::compute_controls(
     vic_command_data.joint_command_velocity * dt;
 
   // Set flags for available commands
+  vic_command_data.has_twist_command = false;
   vic_command_data.has_position_command = true;
   vic_command_data.has_velocity_command = true;
   vic_command_data.has_acceleration_command = false;

cartesian_vic_controller/src/rules/vanilla_cartesian_admittance_rule.cpp

@@ -360,6 +360,7 @@ bool VanillaCartesianImpedanceRule::compute_controls(
 
   // Set flags for available commands
   // ------------------------------------------------
+  vic_command_data.has_twist_command = false;
   vic_command_data.has_position_command = false;
   vic_command_data.has_velocity_command = false;
   vic_command_data.has_acceleration_command = true;