Cannot find node robot_pose_ekf ?

edit

I installed robot_pose_ekf according to http://wiki.ros.org/robot_pose_ekf , but when I run the launch file, thisi is the errer I receive

SUMMARY
========

PARAMETERS
 * /robot_pose_ekf/base_footprint_frame: base_footprint
 * /robot_pose_ekf/freq: 30.0
 * /robot_pose_ekf/imu_used: True
 * /robot_pose_ekf/odom_used: True
 * /robot_pose_ekf/output_frame: odom_combined
 * /robot_pose_ekf/sensor_timeout: 1.0
 * /robot_pose_ekf/vo_used: True
 * /rosdistro: indigo
 * /rosversion: 1.11.21

NODES
  /
    robot_pose_ekf (robot_pose_ekf/robot_pose_ekf)

auto-starting new master
process[master]: started with pid [64634]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to 7023c802-54c3-11e7-8be4-14feb5de14ae
process[rosout-1]: started with pid [64647]
started core service [/rosout]
ERROR: cannot launch node of type [robot_pose_ekf/robot_pose_ekf]: can't locate node [robot_pose_ekf] in package [robot_pose_ekf]

How do I debug thsi error?