Hello, 
I'm not sure whether this is better asked at answers.ros.org, but since it looks like a bug I'm sending it here 

I'm using the tf package and specifically the tf.TransformerROS class in Python. 
If I try calling its methods transformPose or transformPointCloud it returns a LookupException 

    tf.LookupException: Frame id /map does not exist! When trying to transform between /base_link and /map. 

However if I try running the tf_monitor right after that I see that tf has knowledge of the frame 

    ~>rosrun tf tf_monitor base_link map 
    Waiting for transform chain to become available between /base_link and /map 

    RESULTS: for /base_link to /map 
    Chain is: /base_link -> /base_footprint -> /odom_combined -> /map 
    Net delay     avg = 0.00684423: max = 0.054 

    Frames: 
    Frame: /base_footprint published by /robot_pose_ekf Average Delay: 0.0185 Max Delay: 0.026 
    Frame: /base_link published by /robot_state_publisher Average Delay: 0.0075 Max Delay: 0.008 
    Frame: /odom_combined published by /slam_gmapping Average Delay: 0 Max Delay: 0 

    All Broadcasters: 
    Node: /robot_pose_ekf 33.5196 Hz, Average Delay: 0.0185 Max Delay: 0.026 
    Node: /robot_state_publisher 55.5556 Hz, Average Delay: 0.0075 Max Delay: 0.008 
    Node: /slam_gmapping 25 Hz, Average Delay: 0 Max Delay: 0 

I'm running gazebo simulation and have ROBOT=sim set. 

Best, 
Dimitar