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Robot localization and Landmarks

asked 2017-01-24 14:29:36 -0500

haelannaleah gravatar image

updated 2017-01-31 21:06:13 -0500

I am using the robot_localization package on a turtlebot running ROS Indigo. I would like the turtlebot to autonomously navigate a space and update it's position based on AprilTag landmarks. It seems that the way to do this is to take advantage of a map frame. However, when I publish landmark data, the map frame does not update in the discrete jumps I am hoping for. Perhaps I am doing something wrong with the launch file or with the way I am publishing tag data? How do you make sure robot_localization pays attention to the tags? Should I be using the set_pose service instead, or is that only meant to set initial position?

EDIT: Ideally, I would like the map frame to be updated discontinuously when it encounters a landmark, much as the GPS package in robot_localization allows the map frame to be discretely updated. The data published on the apriltags topic is relative to the map frame. There is not currently a transform between the apriltags frame and odom (I am a bit uncertain as to how to approach this). Will publishing a transform as well give discrete updates to position?

FINAL EDIT: Looks like figuring out the tf transformation is the key. I added a tf.TransformBroadcaster to go along with the apriltags publisher, and there were discrete updates; however, it doesn't seem to do what I want with non-zero data. If I publish a zeroed out message and a zeroed out transform, it zeros out the turtlebot. But if I do anything else, the map doesn't update.

My launch file looks like this:

<launch>

<!-- Set up the odom frame (local, continuous navigation) --> 
<node pkg="robot_localization" type="ekf_localization_node" name="ekf_localization_imu" respawn="true" output="screen">
    <param name="map_frame" value="map"/>
    <param name="odom_frame" value="odom"/>
    <param name="base_link_frame" value="base_footprint"/>      
    <param name="world_frame" value="odom"/>                
    <param name="two_d_mode" value="true"/>

    <param name="imu0" value="imu_data"/>
    <rosparam param="imu0_config">
        [false, false, false,
        false, false, true,
        false, false, false,
        false, false, true,
        true, false, false]
    </rosparam>
    <param name="imu0_differential" value="false"/>

    <param name="odom0" value="odom"/>
    <rosparam param="odom0_config">
        [false, false, false,
        false, false, false,
        true, true, false,
        false, false, true,
        false, false, false]
    </rosparam>
    <param name="odom0_differential" value="true"/>

</node>

<!-- Set up the map frame (global, includes jumps) --> 
<node pkg="robot_localization" type="ekf_localization_node" name="ekf_localization_map" respawn="true" output="screen">
    <param name="map_frame" value="map"/>
    <param name="odom_frame" value="odom"/>
    <param name="base_link_frame" value="base_footprint"/>      
    <param name="world_frame" value="map"/>                
    <param name="two_d_mode" value="true"/>

    <param name="imu0" value="imu_data"/>
    <rosparam param="imu0_config">
        [false, false, false,
        false, false, true,
        false, false, false,
        false, false, true,
        true, false, false]
    </rosparam>
    <param name="imu0_differential" value="false"/>

    <param name="odom0" value="odom"/>
    <rosparam param="odom0_config">
        [false, false, false,
        false, false, false,
        true, true, false,
        false, false, true,
        false, false, false]
    </rosparam>
    <param name="odom0_differential" value="true"/>

    <param name="pose0" value = "apriltags"/>
    <rosparam param="pose0_config">
        [true, true, false, 
        false, false, false, 
        false, false, false, 
        false, false, false]
    </rosparam>
    <param name="pose0_differential" value ...
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Comments

Are you certain that the apriltags data is in the map frame, and not relative to the robot? How do you define the global pose of every apriltag? Is there some database that says what their poses in the map frame are?

Tom Moore gravatar imageTom Moore ( 2017-02-01 07:19:35 -0500 )edit

I'm manually publishing the topic, so I know that I intend for it to be in the global frame. The raw tag data is relative to the robot base, but I've been converting it manually for the time being. I need the tag data to tell me where the robot is, so there's an offset from the tag to the robot base

haelannaleah gravatar imagehaelannaleah ( 2017-02-02 13:23:36 -0500 )edit

As to the position of the april tag in the map frame, yes, there is a database containing that information.

haelannaleah gravatar imagehaelannaleah ( 2017-02-02 13:30:48 -0500 )edit

Can you post either a bag file or the code you're using to generate the apriltags -> map transform?

Tom Moore gravatar imageTom Moore ( 2017-03-01 04:09:38 -0500 )edit

Would you like to say the name of the package the you have used ?

Ned gravatar imageNed ( 2018-08-07 04:34:42 -0500 )edit

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answered 2017-01-26 03:08:31 -0500

Tom Moore gravatar image

Your apriltags messages are in the apriltags frame (see the frame_id). Have you provided a transform from apriltags to odom? What is the apriltags frame? Is it relative to the camera? If the filter can't transform the data, it will ignore it. Also, the filter will adjust the measurement covariances to some small epsilon, but you should fill those out.

The set_pose service is not meant to be used for fusion. It's just a way to reset the filter to a specific state.

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Asked: 2017-01-24 14:29:36 -0500

Seen: 734 times

Last updated: Jan 31 '17