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# Commandeering Gazebo Simulation
"Containing all the needs to build a gazebo simulation"
For better look check this note, please visit [HackMD.io](https://hackmd.io/@libernormous/commandeering-gaebo)
by:
[Liber Normous](https://hackmd.io/@libernormous)
---
# Tutorial from scratch part 1
* {%youtube 8ckSl4MbZLg%}
* {%youtube q01dDxeHTMs%}
* http://gazebosim.org/tutorials/?tut=ros_control
* 
* 1. Create gazebo simulation package.
* 2. Create `gazebo_launch.launch` file that includes:
* Setting some parameters.
* Passing that parameter to open `world` file.
* Put in a single `.launch` file.
*
---
# Creating parts using FreeCAD
**STEPS:**
1. Create model.
2. Add center of mass tools.
* 
4. Move the origin of the object to center of mass.
5. Add `FCInfo` to FreeCAD to analyze Inertia etc. https://www.youtube.com/watch?v=gThQk-4p1CY
* 
* Tools Mebu Bar
* Addon manager
* Macros TAB
* Install FCInfo
* Macros Menu Bar
* FCInfo.FCMacro
* Execute
* Set the object density ($\rho(kg/l)$)
* Check `Moment of inertia with mass`
6. Save to spreadsheed 
---
# Create URDF File
**TEMPLATE:**
* https://github.com/ros-simulation/gazebo_ros_demos/blob/kinetic-devel/rrbot_description/urdf/rrbot.xacro
**Tutorial:**
* http://gazebosim.org/tutorials/?tut=ros_urdf
* http://wiki.ros.org/urdf/Tutorials/Building%20a%20Visual%20Robot%20Model%20with%20URDF%20from%20Scratch
* http://gazebosim.org/tutorials?tut=import_mesh
**NOTE:**
* `MESH` needs `FILENAME` attributes. `<mesh filename="/media/zee/53FC06C50A4891B9/Project/m-43-commadeering_gazebo/obstacles-box.dae"/>`
**Check teh URDF FILE:**
```bash=
sudo apt-get install liburdfdom-tools
check_urdf FILE.urdf
```
**Example of URDF file, 1 object, no joints:**
```xml=
<?xml version="1.0"?>
<!-- Simple BOX -->
<robot name="box1" xmlns:xacro="http://www.ros.org/wiki/xacro">
<!-- Base Link -->
<link name="link1">
<collision>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<mesh filename="/media/zee/53FC06C50A4891B9/Project/m-43-commadeering_gazebo/obstacles-box.dae"/>
</geometry>
</collision>
<visual>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<mesh filename="/media/zee/53FC06C50A4891B9/Project/m-43-commadeering_gazebo/obstacles-box.dae"/>
</geometry>
<material name="orange"/>
</visual>
<inertial>
<origin xyz="0 0 0" rpy="0 0 0"/>
<mass value="0.525"/>
<inertia
ixx="7109.374999999998" ixy="0.0" ixz="0.0"
iyy="16296.874999999998" iyz="0.0"
izz="12687.500000000002"/>
</inertial>
</link>
</robot>
```
---
# Create SDF file (does not work on RVIZ)
**Template and Tutorial:** http://gazebosim.org/tutorials?tut=build_model
---
# Terminal functionality
## Spawning object using `gazebo` package
[**Services: Create and destroy models in simulation**
](http://gazebosim.org/tutorials/?tut=ros_comm)
**NOTE:**
* `model_xml` is the file. not the path
```bash=
rosservice call /gazebo/spawn_urdf_model "model_name: 'box1'
model_xml: '$(cat /media/zee/53FC06C50A4891B9/Project/m-43-commadeering_gazebo/box1.urdf)'
robot_namespace: ''
initial_pose:
position: {x: 0.0, y: 0.0, z: 0.0}
orientation: {x: 0.0, y: 0.0, z: 0.0, w: 0.0}
reference_frame: ''"
```
---
## Deleting object `gazebo` package
[**Services: Create and destroy models in simulation**
](http://gazebosim.org/tutorials/?tut=ros_comm)
```bash=
rosservice call /gazebo/delete_model "model_name: 'box1'"
```
---
## Teleporting object to other location
**NOTE:**
* This is affecting the odometry reading!
* Set the position and orientation. Not the TWIST. Twist will be overwritten by `/cmd_vel`
```bash
rosservice call /gazebo/set_model_state "model_state:
model_name: 'neuronbot2'
pose:
position:
x: -3
y: 1.0
z: 0.0
orientation:
x: 0.0
y: 0.0
z: 0.0
w: 0.0
twist:
linear:
x: 0.0
y: 0.0
z: 0.0
angular:
x: 0.0
y: 0.0
z: 0.0
reference_frame: ''"
```
---
# MATLAB add, delete, move, getting states of models
**NOTE**:
* This methods are inside a class. That is why we have `obj.` on every variables.
* `model_state` input is in format of $[x\ \ y\ \ \theta]$
## Add model
**Preparing variables:**
```c=
obj.add_srv_cli = rossvcclient('/gazebo/spawn_urdf_model');
obj.add_srv_msg = rosmessage(obj.add_srv_cli);
```
**Calling a ROS service:"**
* Object is always drop from 1m above for simplicity
```c=
function obj = add_model(obj,model_name, model_state, urdf_string)
% assign message
obj.add_srv_msg.ModelName = model_name;
obj.add_srv_msg.ModelXml = urdf_string;
obj.add_srv_msg.InitialPose.Position.X = model_state(1);
obj.add_srv_msg.InitialPose.Position.Y = model_state(2);
obj.add_srv_msg.InitialPose.Position.Z = 1;
% OUTPUT: Q, is an N-by-4 matrix containing N quaternions.
% Each quaternion is of the form q = [w x y z], with w as the
% scalar number.
% INPUT: By default, the ZYX axis order will be used.
Q = eul2quat([model_state(3) 0 0]);
obj.add_srv_msg.InitialPose.Orientation.W = Q(1);
obj.add_srv_msg.InitialPose.Orientation.X = Q(2);
obj.add_srv_msg.InitialPose.Orientation.Y = Q(3);
obj.add_srv_msg.InitialPose.Orientation.Z = Q(4);
%call service
call(obj.add_srv_cli, obj.add_srv_msg);
end
```
**How to read URDF file into string in MATLAB**
```c=
% reading urdf
f_id = fopen('/media/zee/53FC06C50A4891B9/Project/m-43-commadeering_gazebo/urdf/box1.urdf');
% Read all lines & collect in cell array
urdf_txt = fscanf(f_id,'%c');
```
## Delete a model
**Preparing variables:**
```c=
% delete model sservice
obj.del_srv_cli = rossvcclient('/gazebo/delete_model');
obj.del_srv_msg = rosmessage(obj.del_srv_cli);
```
**Calling a ROS service:"**
```c=
function obj = del_model(obj,model_name)
% assign message
obj.del_srv_msg.ModelName = model_name;
%call service
call(obj.del_srv_cli, obj.del_srv_msg);
end
```
## Get model states
**NOTE:**
* We Get states not from ***service***. But from Subscribing into a ***topic***.
* This is done because we need to update the states everytime and the easiest way is using `callback` function.
* Callback function will update the states whenever there is a state change.
* Iside the callback function `delay` or `pause` is necessary. `¯\_(ツ)_/¯
`.
**Preparing variables:**
```c=
% subscribe to model states
disp('subscribing /gazebo/model_states: pause 2s');
obj.model_states_msg = rosmessage('gazebo_msgs/ModelStates');
pause(2);
obj.model_states_sub = rossubscriber('/gazebo/model_states',@obj.model_states_cb);
```
**Extracting message from the topic:**
```c=
function state_val = get_state(obj,model_name)
index = strcmp(obj.model_names,model_name);
state_X = obj.model_states_msg.Pose(index).Position.X;
state_Y = obj.model_states_msg.Pose(index).Position.Y;
state_roll = obj.model_states_msg.Pose(index).Orientation.X;
state_pitch = obj.model_states_msg.Pose(index).Orientation.Y;
state_yaw = obj.model_states_msg.Pose(index).Orientation.Z;
state_mag = obj.model_states_msg.Pose(index).Orientation.W;
% INPUT: The default rotation sequence is q = [w x y z]
% OUTPUT: The default rotation sequence is 'ZYX'
eul = quat2eul([state_mag state_roll state_pitch state_yaw]);
state_val=[state_X state_Y eul(1)];
end
```
**Call back function:**
```c=
function obj = model_states_cb(obj,~,message)
obj.model_states_msg = message;
obj.model_names = obj.model_states_msg.Name;
pause(0.05);
end
```
## Move a model
**NOTE**
* Moving here is limited to $[X\ \ Y\ \ \theta]$ dirrection for simplicity.
* To move, we need to know the current $Z$ axis position value.
* We get $Z$ axis position value from subscribing to `'/gazebo/model_states'`.
*
**Preparing variables:**
```c=
% set state model service
obj.set_srv_cli = rossvcclient('/gazebo/set_model_state');
obj.set_srv_msg = rosmessage(obj.set_srv_cli);
```
**Calling a ROS service:"**
```c=
function obj = set_state(obj, model_name, model_state)
index = strcmp(obj.model_names,model_name);
% assign message
obj.set_srv_msg.ModelState.ModelName = model_name;
% assign message
obj.set_srv_msg.ModelState.ModelName = model_name;
obj.set_srv_msg.ModelState.Pose.Position.X = model_state(1);
obj.set_srv_msg.ModelState.Pose.Position.Y = model_state(2);
obj.set_srv_msg.ModelState.Pose.Position.Z = obj.model_states_msg.Pose(index).Position.Z;
% OUTPUT: Q, is an N-by-4 matrix containing N quaternions.
% Each quaternion is of the form q = [w x y z], with w as the
% scalar number.
% INPUT: By default, the ZYX axis order will be used.
Q = eul2quat([model_state(3) 0 0]);
obj.set_srv_msg.ModelState.Pose.Orientation.W = Q(1);
obj.set_srv_msg.ModelState.Pose.Orientation.X = Q(2);
obj.set_srv_msg.ModelState.Pose.Orientation.Y = Q(3);
obj.set_srv_msg.ModelState.Pose.Orientation.Z = Q(4);
%call service
call(obj.set_srv_cli, obj.set_srv_msg);
end
```
---
###### tags: `Web Clipper`
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