Thanks I really appreciate your response. This solution worked to address that error. However, I am facing a new issue now. After sourcing the setup.bash file in devel_isolated and running the launch file (continuous_detection.launch), I get the following warning

[WARN} : remove_duplicates parameter not provided. Defaulting to true.

After I run rqt_image_view to the see the camera feed and detection, the /tag_detections_image topic (or other topics such as tag_Detections_image/compressed or tag_detections_image/compressedDepth or tag_detections_image/theora) shows a grey blurred static image and even I show a marker at the raspberry pi camera of the turtlebot nothing gets detected.

Could you please let me know what I might be doing wrong?

Thanks again for your time and help

I'm not really sure about this, are you sure your camera is working, do you see the image on rviz? Also did you add the tag definitions in the tags.yaml file? ( apriltag_ros/config/tags.yaml )

yes, the camera does work but the tags.yaml seems to be empty bunch of lines commented (starts with #) and just two more things in there (below) standalone_tags: [ ] tag_bundles: [ ]

Could you suggest what to add in there if I would like to detect april tag 36h11 tags?

also i just noticed that settings.yaml has details regarding tag family

You would have to specify the tags in the yaml file. I'd recommend going through the tutorials [http://wiki.ros.org/apriltag_ros]

I do have exactly what they have in the repository file which is the following

(contents of tags.yaml)

# Definitions of tags to detect

#

## General remarks

#

- All length in meters

- Ellipsis (...) signifies that the previous element can be repeated multiple times.

#

## Standalone tag definitions

### Remarks

#

- name is optional

#

### Syntax

#

standalone_tags:

[

{id: ID, size: SIZE, name: NAME},

...

]

standalone_tags: [ ]

## Tag bundle definitions

### Remarks

#

- name is optional

- x, y, z have default values of 0 thus they are optional

- qw has default value of 1 and qx, qy, qz have default values of 0 thus they are optional

#

### Syntax

#

tag_bundles:

[

{

name: 'CUSTOM_BUNDLE_NAME',

layout:

[

{id: ID, size: SIZE, x: X_POS, y: Y_POS, z: Z_POS, qw: QUAT_W_VAL, qx: QUAT_X_VAL, qy: QUAT_Y_VAL, qz: QUAT_Z_VAL},

...

]

},

...

]

tag_bundles: [ ]

You actually have to define tags for them to be detected, If you don't specify the id and size it wouldn't know what to look for.

standalone_tags:
  [
    {id: 0, size: .1524},
    {id: 1, size: .1524},
    {id: 2, size: .1524},
  ]

Hey is this issue resolved? Even I am facing the same issue. 1) I added the standalone tags in the tags.yaml but in the rqt_image_view tab I can see the image but it is not showing up in the rviz. 2) Even the raspi_cam node is free in the rqt graph, it is not subscribing to the tag_detection_image topic.