diff --git a/examples/worlds/shapes_population.sdf b/examples/worlds/3k_shapes.sdf
similarity index 100%
rename from examples/worlds/shapes_population.sdf
rename to examples/worlds/3k_shapes.sdf
diff --git a/examples/worlds/actors_population.sdf b/examples/worlds/actors_population.sdf
deleted file mode 100644
index a89325da0e..0000000000
--- a/examples/worlds/actors_population.sdf
+++ /dev/null
@@ -1,2841 +0,0 @@
-<?xml version="1.0" ?>
-<!--
-  To generate sdf file using this erb template, run `erb -T 1 actors_population.sdf.erb > actors_population.sdf`
--->
-<sdf version="1.6">
-  <world name="actors">
-    <plugin
-      filename="libignition-gazebo-physics-system.so"
-      name="ignition::gazebo::systems::Physics">
-    </plugin>
-    <plugin
-      filename="libignition-gazebo-user-commands-system.so"
-      name="ignition::gazebo::systems::UserCommands">
-    </plugin>
-    <plugin
-      filename="libignition-gazebo-scene-broadcaster-system.so"
-      name="ignition::gazebo::systems::SceneBroadcaster">
-    </plugin>
-
-    <gui fullscreen="0">
-      <!-- 3D scene -->
-      <plugin filename="GzScene3D" name="3D View">
-        <ignition-gui>
-          <title>3D View</title>
-          <property type="bool" key="showTitleBar">false</property>
-          <property type="string" key="state">docked</property>
-        </ignition-gui>
-
-        <engine>ogre2</engine>
-        <scene>scene</scene>
-        <ambient_light>0.4 0.4 0.4</ambient_light>
-        <background_color>0.8 0.8 0.8</background_color>
-        <camera_pose>-6 0 6 0 0.5 0</camera_pose>
-      </plugin>
-
-      <!-- World control -->
-      <plugin filename="WorldControl" name="World control">
-        <ignition-gui>
-          <title>World control</title>
-          <property type="bool" key="showTitleBar">false</property>
-          <property type="bool" key="resizable">false</property>
-          <property type="double" key="height">72</property>
-          <property type="double" key="width">121</property>
-          <property type="double" key="z">1</property>
-
-          <property type="string" key="state">floating</property>
-          <anchors target="3D View">
-            <line own="left" target="left"/>
-            <line own="bottom" target="bottom"/>
-          </anchors>
-        </ignition-gui>
-
-        <play_pause>true</play_pause>
-        <step>true</step>
-        <start_paused>true</start_paused>
-        <service>/world/actors/control</service>
-        <stats_topic>/world/actors/stats</stats_topic>
-
-      </plugin>
-
-      <!-- World statistics -->
-      <plugin filename="WorldStats" name="World stats">
-        <ignition-gui>
-          <title>World stats</title>
-          <property type="bool" key="showTitleBar">false</property>
-          <property type="bool" key="resizable">false</property>
-          <property type="double" key="height">110</property>
-          <property type="double" key="width">290</property>
-          <property type="double" key="z">1</property>
-
-          <property type="string" key="state">floating</property>
-          <anchors target="3D View">
-            <line own="right" target="right"/>
-            <line own="bottom" target="bottom"/>
-          </anchors>
-        </ignition-gui>
-
-        <sim_time>true</sim_time>
-        <real_time>true</real_time>
-        <real_time_factor>true</real_time_factor>
-        <iterations>true</iterations>
-        <topic>/world/actors/stats</topic>
-
-      </plugin>
-
-      <!-- Entity tree -->
-      <plugin filename="EntityTree" name="Entity tree">
-        <ignition-gui>
-          <property type="bool" key="showTitleBar">false</property>
-          <property type="string" key="state">docked</property>
-        </ignition-gui>
-      </plugin>
-
-    </gui>
-
-    <light type="directional" name="sun">
-      <cast_shadows>true</cast_shadows>
-      <pose>0 0 10 0 0 0</pose>
-      <diffuse>0.8 0.8 0.8 1</diffuse>
-      <specular>0.2 0.2 0.2 1</specular>
-      <attenuation>
-        <range>1000</range>
-        <constant>0.9</constant>
-        <linear>0.01</linear>
-        <quadratic>0.001</quadratic>
-      </attenuation>
-      <direction>-0.5 0.1 -0.9</direction>
-    </light>
-
-    <model name="ground_plane">
-      <static>true</static>
-      <link name="link">
-        <collision name="collision">
-          <geometry>
-            <plane>
-              <normal>0.0 0.0 1</normal>
-            </plane>
-          </geometry>
-        </collision>
-        <visual name="visual">
-          <geometry>
-            <plane>
-              <normal>0.0 0.0 1</normal>
-              <size>100 100</size>
-            </plane>
-          </geometry>
-          <material>
-            <ambient>0.8 0.8 0.8 1</ambient>
-            <diffuse>0.8 0.8 0.8 1</diffuse>
-            <specular>0.8 0.8 0.8 1</specular>
-          </material>
-        </visual>
-      </link>
-    </model>
-
-    <include>
-      <uri>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor</uri>
-    </include>
-
-    
-    <actor name="actor_1">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="1" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>-3 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>-3 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_2">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="2" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>-1 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>-1 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_3">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="3" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>1 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>1 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_4">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="4" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>3 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>3 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_5">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="5" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>5 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>5 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_6">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="6" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>7 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>7 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_7">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="7" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>9 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>9 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_8">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="8" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>11 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>11 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_9">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="9" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>13 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>13 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_10">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="10" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>15 5 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>15 5 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_11">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="11" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>-3 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>-3 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_12">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="12" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>-1 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>-1 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_13">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="13" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>1 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>1 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_14">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="14" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>3 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>3 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_15">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="15" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>5 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>5 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_16">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="16" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>7 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>7 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_17">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="17" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>9 3 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>9 3 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_18">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
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-            <time>30</time>
-            <pose>7 -11 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_87">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="87" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>9 -11 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>9 -11 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_88">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="88" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>11 -11 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>11 -11 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_89">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="89" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>13 -11 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>13 -11 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_90">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="90" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>15 -11 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>15 -11 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_91">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="91" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>-3 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>-3 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_92">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="92" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>-1 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>-1 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_93">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="93" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>1 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>1 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_94">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="94" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>3 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>3 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_95">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="95" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>5 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>5 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_96">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="96" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>7 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>7 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_97">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="97" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>9 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>9 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_98">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="98" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>11 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>11 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_99">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="99" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>13 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>13 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-    
-    <actor name="actor_100">
-      <skin>
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>1.0</scale>
-      </skin>
-      <animation name="talk_b">
-        <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
-        <scale>0.055</scale>
-        <interpolate_x>true</interpolate_x>
-      </animation>
-      <script>
-        <loop>true</loop>
-        <auto_start>true</auto_start>
-        <trajectory id="100" type="talk_b">
-          <waypoint>
-            <time>0</time>
-            <pose>15 -13 1.0 0 0 0</pose>
-          </waypoint>
-          <waypoint>
-            <time>30</time>
-            <pose>15 -13 1.0 0 0 0</pose>
-          </waypoint>
-        </trajectory>
-      </script>
-    </actor>
-
-      </world>
-</sdf>
diff --git a/examples/worlds/actors_population.sdf.erb b/examples/worlds/actors_population.sdf.erb
index 1394a51754..855d89f2ba 100644
--- a/examples/worlds/actors_population.sdf.erb
+++ b/examples/worlds/actors_population.sdf.erb
@@ -1,6 +1,10 @@
 <?xml version="1.0" ?>
 <!--
-  To generate sdf file using this erb template, run `erb -T 1 actors_population.sdf.erb > actors_population.sdf`
+  To generate sdf file using this erb template,
+  run `erb actors_population.sdf.erb > actors_population.sdf`
+  To specify number of actors,
+  run `erb r=10 c=10 actors_population.sdf.erb > actors_population.sdf`
+  where `r` means row, `c` means column, and population = r * c.
 -->
 <sdf version="1.6">
   <world name="actors">
@@ -133,18 +137,27 @@
       </link>
     </model>
 
-    <include>
-      <uri>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor</uri>
-    </include>
-
     <%
-      # number of population
-      total = 10
-      for i in (0..total-1)
-        for j in (1..total)
+      vars = ARGV.take_while {|arg| arg[/^\w+=/]}
+      ARGV.slice!(0, vars.size)
+      vars.each do |var|
+      k, v = var.split('=', 2)
+      TOPLEVEL_BINDING.eval %Q(#{k} = "#{v}")
+      end
+      # population = column * row, default to 100 actors
+      column = 10
+      row = 10
+      if (defined? c)
+        column = c.to_i
+      end
+      for j in (0..column-1)
+        if (defined? r)
+          row = r.to_i
+        end
+        for i in (0..row-1)
     %>
 
-    <actor name="actor_<%= 10*i+j %>">
+    <actor name="actor_<%= j*column + i %>">
       <skin>
         <filename>https://fuel.ignitionrobotics.org/1.0/Mingfei/models/actor/tip/files/meshes/talk_b.dae</filename>
         <scale>1.0</scale>
@@ -157,14 +170,14 @@
       <script>
         <loop>true</loop>
         <auto_start>true</auto_start>
-        <trajectory id="<%= 10*i+j %>" type="talk_b">
+        <trajectory id="<%= j*column + i %>" type="talk_b">
           <waypoint>
             <time>0</time>
-            <pose><%= -5 + 2*j %> <%= 5 + -2*i %> 1.0 0 0 0</pose>
+            <pose><%= -(row/2) + i %> <%= j %> 1.0 0 0 0</pose>
           </waypoint>
           <waypoint>
             <time>30</time>
-            <pose><%= -5 + 2*j %> <%= 5 + -2*i %> 1.0 0 0 0</pose>
+            <pose><%= -(row/2) + i %> <%= j %> 1.0 0 0 0</pose>
           </waypoint>
         </trajectory>
       </script>