<?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>
<!--##################################################################################-->
<!-- ######## cylinder ######### -->
<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>
<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>
<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>
<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>
<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>
<!--##################################################################################-->
<!-- 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>
<!--##################################################################################-->
</link>
<!--##################################################################################-->
<!-- 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>
<!--##################################################################################-->
</model>
</world>
</sdf>
1. 傳感器
傳感器的添加，以激光傳感器velodynelidar爲例，gazebo中的激光傳感器可以發出一個或多個光束，這些光束會產生距離以及可能的強度數據。
在sdf文件中，該傳感器由<scan>和<range>兩個部分組成，<scan>定義波束的佈局和數量，<range>限定一個單獨的束的性質
<scan>中包含<horizontal>和<vertical>兩個塊。<horizontal>組件定義在水平平面中發出的光線，該<vertical>組件定義在垂直平面中發出的光線。
2. 關節測試
打開右面板可設置力、位置、速度等參數，單擊開始方針即可看到效果。
右面板的打開：點擊右側豎着的
.....，並向左拖動，即可打開默認隱藏的右面板！
Ctrl+R復原world環境
3. 模型外觀
需要的工具：freecad、blender
sudo apt-get install freecad
sudo apt-get install blender
具體設置參考這兒：http://gazebosim.org/tutorials?cat=guided_i&tut=guided_i2
最終效果如下：
4. 傳感器噪聲
內置高斯噪聲～
Ctrl+T打開topic visualization
在<sensor>的子標籤<ray>中添加如下代碼：
<noise>
<!-- Use gaussian noise -->
<type>gaussian</type>
<mean>0.0</mean>
<stddev>0.1</stddev>
</noise>
通過<mean>、<stddev>即可修改噪聲幅度。
重新加載，發現信號不在圓滑！
參考文獻：