Rviz reporting no fixed frame

edit

I'm trying to complete the robot state publisher tutorial, but when I run:

roslaunch myrobot_description myrobot_rviz.launch

Rviz shows no model and in the left-hand panel reports the error "Fixed Frame [map] does not exist".

myrobot.urdf.xarco:

<?xml version="1.0"?>
<robot name="myrobot"
    xmlns:xacro="http://www.ros.org/wiki/xacro">

    <xacro:macro name="default_inertial" params="mass">
        <inertial>
                <mass value="${mass}" />
                <inertia
                    ixx="1.0" ixy="0.0" ixz="0.0"
                    iyy="1.0" iyz="0.0" izz="1.0" />
        </inertial>
    </xacro:macro>

    <xacro:include filename="$(find myrobot_description)/urdf/materials.urdf.xacro" />

    <!-- width in meters -->
    <property name="torso_x_size" value="0.1" />

    <!-- length in meters -->
    <property name="torso_y_size" value="0.205" />

    <!-- height in meters -->
    <property name="torso_z_size" value="0.03" />

    <!-- torso mass (not including legs) in kg -->
    <property name="torso_mass" value="0.920" />

    <!-- mass of a single upper leg piece in kg -->
    <property name="upper_leg_mass" value="0.010" />

    <link name="base_link">
        <visual>
            <geometry>
                <box size="${torso_x_size} ${torso_y_size} ${torso_z_size}" />
            </geometry>
            <material name="red"/>
        </visual>
        <collision>
            <geometry>
                <box size="${torso_x_size} ${torso_y_size} ${torso_z_size}" />
            </geometry>
        </collision>
        <xacro:default_inertial mass="${torso_mass}"/>
    </link>
    <xacro:macro name="leg" params="name reflect_x reflect_y">
        <link name="${name}">
            <visual>
                <geometry>
                    <box size="0.003 0.04 0.005" />
                </geometry>
                <origin xyz="0 0.04 0" rpy="0 0 0"/>
                <material name="blue" />
            </visual>
            <collision>
                <geometry>
                    <box size="0.003 0.04 0.005" />
                </geometry>
                <origin xyz="0 0.04 0" rpy="0 0 0"/>
            </collision>
            <xacro:default_inertial mass="${upper_leg_mass}"/>
        </link>
        <joint name="torso_to_${name}" type="fixed">
            <parent link="base_link"/>
            <child link="${name}"/>
            <origin xyz="${torso_x_size/2*reflect_x} ${torso_y_size/2*reflect_y} 0" />
            <axis xyz="0 1 0" rpy="0 0 0" />
        </joint>
    </xacro:macro>
    <xacro:leg name="front_right_leg" reflect_x="1" reflect_y="1" />
</robot>

myrobot_rviz.launch:

<launch>
  <param name="robot_description" command="$(find xacro)/xacro.py '$(find myrobot_description)/urdf/myrobot.urdf.xacro'" />

  <!-- source that publishes the joint positions as a sensor_msgs/JointState -->
  <param name="use_gui" value="true"/>
  <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" />

  <!-- robot visualization -->
  <node name="rviz" pkg="rviz" type="rviz" required="true" />

  <!-- publish all the frames to TF -->
  <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher">
    <param name="publish_frequency" value="50"/> <!-- Hz -->
  </node>
</launch>

I googled that error, and other pages claim the it means there's no base_link defined in my model, but there clearly is. What am I doing wrong?

Edit: I changed my launch file to:

<launch>
    <arg name="model" />
    <arg name="gui" default="True" />
    <param name="robot_description" command="$(find xacro)/xacro.py $(arg model)" />
    <param name="use_gui" value="$(arg gui)"/>
    <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" />
    <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher">
        <param name="publish_frequency" value="50"/> <!-- Hz -->
    </node>
    <node name="rviz" pkg="rviz" type="rviz" args="-d $(find myrobot_description)/urdf.rviz" required="true" />
</launch>

and now call it like:

roslaunch myrobot_description myrobot_rviz.launch model:='$(find myrobot_description)/urdf/myrobot.urdf.xacro'

and that makes the model show in Rviz, but it doesn't look any different from a the other xacrodisplay launches the tutorial goes over. Is the tutorial incomplete, or am I ... (more)