\qquad ① 创建模型目录
mkdir -p ~/.gazebo/models/my_robot
\qquad ② 创建模型配置文件
gedit ~/.gazebo/models/my_robot/model.config
\qquad 元数据（config）内容如下：
<?xml version="1.0"?>
<model>
<name>My Robot</name>
<version>1.0</version>
<sdf version='1.4'>model.sdf</sdf>
<author>
<name>My Name</name>
<email>me@my.email</email>
</author>
<description>
My awesome robot.
</description>
</model>
\qquad ② 创建模型配置文件
gedit ~/.gazebo/models/my_robot/model.sdf
\qquad 必要标记（sdf）内容如下：
<?xml version='1.0'?>
<sdf version='1.4'>
<model name="my_robot">
</model>
</sdf>
\qquad ① 令机器人模型静态
注意：在static标签后将会在link标签下生成对应部件，通过collision的name隔开，故在后代码展示中则会忽略一部分，请自行补充
<?xml version='1.0'?>
<sdf version='1.4'>
<model name="my_robot">
<static>true</static>
</model>
</sdf>
\qquad ② 创建长方体的底座
代码解释：
- box 标签，用于产生对应尺寸的长方体
- collision 标签，指定碰撞尺寸
- visual 标签，指定视觉尺寸，常见情况下与collision相同
<?xml version='1.0'?>
<sdf version='1.4'>
<model name="my_robot">
<static>true</static>
<link name='chassis'>
<pose>0 0 .1 0 0 0</pose>
<collision name='collision'>
<geometry>
<box>
<size>.4 .2 .1</size>
</box>
</geometry>
</collision>
<visual name='visual'>
<geometry>
<box>
<size>.4 .2 .1</size>
</box>
</geometry>
</visual>
</link>
</model>
</sdf>
\qquad ③ 创建脚轮（万向轮）
注意：脚轮固定在底座上，故二者同属一个link
<collision name='caster_collision'>
<pose>-0.15 0 -0.05 0 0 0</pose>
<geometry>
<sphere>
<radius>.05</radius>
</sphere>
</geometry>
<surface>
<friction>
<ode>
<mu>0</mu>
<mu2>0</mu2>
<slip1>1.0</slip1>
<slip2>1.0</slip2>
</ode>
</friction>
</surface>
</collision>
<visual name='caster_visual'>
<pose>-0.15 0 -0.05 0 0 0</pose>
<geometry>
<sphere>
<radius>.05</radius>
</sphere>
</geometry>
</visual>
</link>
\qquad ④ 创建前轮和后轮
注意：前轮和后轮分别创建了新的link
<link name="left_wheel">
<pose>0.1 0.13 0.1 0 1.5707 1.5707</pose>
<collision name="collision">
<geometry>
<cylinder>
<radius>.1</radius>
<length>.05</length>
</cylinder>
</geometry>
</collision>
<visual name="visual">
<geometry>
<cylinder>
<radius>.1</radius>
<length>.05</length>
</cylinder>
</geometry>
</visual>
</link>
<link name="right_wheel">
<pose>0.1 -0.13 0.1 0 1.5707 1.5707</pose>
<collision name="collision">
<geometry>
<cylinder>
<radius>.1</radius>
<length>.05</length>
</cylinder>
</geometry>
</collision>
<visual name="visual">
<geometry>
<cylinder>
<radius>.1</radius>
<length>.05</length>
</cylinder>
</geometry>
</visual>
</link>
\qquad ⑤ 导入Gazebo可视化模型
注意：修改SDF文件后，只需要删除原有模型重新插入就会更新模型
<static>false</static>
<joint type="revolute" name="left_wheel_hinge">
<pose>0 0 -0.03 0 0 0</pose>
<child>left_wheel</child>
<parent>chassis</parent>
<axis>
<xyz>0 1 0</xyz>
</axis>
</joint>
<joint type="revolute" name="right_wheel_hinge">
<pose>0 0 0.03 0 0 0</pose>
<child>right_wheel</child>
<parent>chassis</parent>
<axis>
<xyz>0 1 0</xyz>
</axis>
</joint>
.world文件： gedit velodyne.world
<?xml version="1.0" ?>
<sdf version="1.5">
<world name="default">
<!-- A global light source -->
<include>
<uri>model://sun</uri>
</include>
<!-- A ground plane -->
<include>
<uri>model://ground_plane</uri>
</include>
</world>
</sdf>
<model name="velodyne_hdl-32">
<!-- Give the base link a unique name -->
<link name="base">
<!-- Offset the base by half the lenght of the cylinder -->
<pose>0 0 0.029335 0 0 0</pose>
<collision name="base_collision">
<geometry>
<cylinder>
<!-- Radius and length provided by Velodyne -->
<radius>.04267</radius>
<length>.05867</length>
</cylinder>
</geometry>
</collision>
<!-- The visual is mostly a copy of the collision -->
<visual name="base_visual">
<geometry>
<cylinder>
<radius>.04267</radius>
<length>.05867</length>
</cylinder>
</geometry>
</visual>
</link>
<!-- Give the base link a unique name -->
<link name="top">
<!-- Vertically offset the top cylinder by the length of the bottom
cylinder and half the length of this cylinder. -->
<pose>0 0 0.095455 0 0 0</pose>
<collision name="top_collision">
<geometry>
<cylinder>
<!-- Radius and length provided by Velodyne -->
<radius>0.04267</radius>
<length>0.07357</length>
</cylinder>
</geometry>
</collision>
<!-- The visual is mostly a copy of the collision -->
<visual name="top_visual">
<geometry>
<cylinder>
<radius>0.04267</radius>
<length>0.07357</length>
</cylinder>
</geometry>
</visual>
</link>
</model>
cd ~/
gazebo velodyne.world -u
注意：紫色框对应关联的链接大小，此时模型没有惯性信息，故尺寸过大
在< link name=“base” >块中添加以下内容：
<link name="base">
<pose>0 0 0.029335 0 0 0</pose>
<inertial>
<mass>1.2</mass>
<inertia>
<ixx>0.001087473</ixx>
<iyy>0.001087473</iyy>
<izz>0.001092437</izz>
<ixy>0</ixy>
<ixz>0</ixz>
<iyz>0</iyz>
</inertia>
</inertial>
在< link name=“top” >块中添加以下内容：
<link name="top">
<pose>0 0 0.095455 0 0 0</pose>
<inertial>
<mass>0.1</mass>
<inertia>
<ixx>0.000090623</ixx>
<iyy>0.000090623</iyy>
<izz>0.000091036</izz>
<ixy>0</ixy>
<ixz>0</ixz>
<iyz>0</iyz>
</inertia>
</inertial>
最终效果如下：
<!-- Each joint must have a unique name -->
<joint type="revolute" name="joint">
<!-- Position the joint at the bottom of the top link -->
<pose>0 0 -0.036785 0 0 0</pose>
<!-- Use the base link as the parent of the joint -->
<parent>base</parent>
<!-- Use the top link as the child of the joint -->
<child>top</child>
<!-- The axis defines the joint's degree of freedom -->
<axis>
<!-- Revolve around the z-axis -->
<xyz>0 0 1</xyz>
<!-- Limit refers to the range of motion of the joint -->
<limit>
<!-- Use a very large number to indicate a continuous revolution -->
<lower>-10000000000000000</lower>
<upper>10000000000000000</upper>
</limit>
</axis>
</joint>
1. 启动Gazebo，右键单击模型，选择View->Joints，View->Transparent
2. 打开右面板，选择Velodyne模型。使用Force选项卡向关节施加较小的，可看到关节旋转即可
激光传感器，可以发出一个或多个光束，光束产生距离和强度数据，对应SDF文件中的< scan >和< range >，分别对应波束的布局、数量和限定束的性质，其中< scan >中包含< horizontal >和< vertical >两个块。< horizontal >组件定义在水平平面中发出的光线，该< vertical >组件定义在垂直平面中发出的光线，Velodyne传感器需要垂直射线，然后旋转。我们将其模拟为旋转的水平扇面。
<!-- Add a ray sensor, and give it a name -->
<sensor type="ray" name="sensor">
<!-- Position the ray sensor based on the specification. Also rotate
it by 90 degrees around the X-axis so that the <horizontal> rays
become vertical -->
<pose>0 0 -0.004645 1.5707 0 0</pose>
<!-- Enable visualization to see the rays in the GUI -->
<visualize>true</visualize>
<!-- Set the update rate of the sensor -->
<update_rate>30</update_rate>
<ray>
<!-- The scan element contains the horizontal and vertical beams.
We are leaving out the vertical beams for this tutorial. -->
<scan>
<!-- The horizontal beams -->
<horizontal>
<!-- The velodyne has 32 beams(samples) -->
<samples>32</samples>
<!-- Resolution is multiplied by samples to determine number of
simulated beams vs interpolated beams. See:
http://sdformat.org/spec?ver=1.6&elem=sensor#horizontal_resolution
-->
<resolution>1</resolution>
<!-- Minimum angle in radians -->
<min_angle>-0.53529248</min_angle>
<!-- Maximum angle in radians -->
<max_angle>0.18622663</max_angle>
</horizontal>
</scan>
<!-- Range defines characteristics of an individual beam -->
<range>
<!-- Minimum distance of the beam -->
<min>0.05</min>
<!-- Maximum distance of the beam -->
<max>70</max>
<!-- Linear resolution of the beam -->
<resolution>0.02</resolution>
</range>
</ray>
</sensor>
在< sensor >的子标签< ray >中添加如下代码：
<noise> <!-- Use gaussian noise --> <type>gaussian</type> <mean>0.0</mean> <stddev>0.1</stddev> </noise>效果如下：
