<?xml version="1.0" ?>
<!-- 使用自包含的 SDF world，避免 Fortress 环境中找不到 sun / ground_plane 模型资源。 -->
<sdf version="1.8">
  <world name="default">
    <gravity>0 0 -9.8</gravity>

    <scene>
      <ambient>0.4 0.4 0.4 1.0</ambient>
      <background>0.8 0.8 0.8 1.0</background>
      <shadows>true</shadows>
    </scene>

    <light name="sun" type="directional">
      <cast_shadows>true</cast_shadows>
      <pose>0 0 10 0 0 0</pose>
      <diffuse>0.8 0.8 0.8 1.0</diffuse>
      <specular>0.2 0.2 0.2 1.0</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 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
        </collision>
        <visual name="visual">
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
          <material>
            <ambient>0.85 0.85 0.85 1.0</ambient>
            <diffuse>0.85 0.85 0.85 1.0</diffuse>
            <specular>0.1 0.1 0.1 1.0</specular>
          </material>
        </visual>
      </link>
    </model>
  </world>
</sdf>
