Users Manual

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"message": "string",
"value": "int16"
},
"tags": [
{
"id": "string",
"instance
_
id": "string",
"pose": {
"orientation": {
"w": "float64",
"x": "float64",
"y": "float64",
"z": "float64"
},
"position": {
"x": "float64",
"y": "float64",
"z": "float64"
}
},
"pose
_
frame": "string",
"size": "float64",
"timestamp": {
"nsec": "int32",
"sec": "int32"
}
}
],
"timestamp": {
"nsec": "int32",
"sec": "int32"
}
}
Request: tags is the list of tag IDs that the TagDetect component should detect. For QR codes, the ID is
the contained data. For AprilTags, it is “<family>_<id>”, so, e.g., for a tag of family 36h11 and ID
5, it is “36h11_5”. Naturally, the AprilTag component can only be triggered for AprilTags, and the
QR code component only for QR codes.
The tags list can also be left empty. In that case, all detected tags will be returned. This feature should
be used only during development and debugging of an application. Whenever possible, the concrete
tag IDs should be listed, on the one hand avoiding some false positives, on the other hand speeding up
tag detection by filtering tags not of interest.
For AprilTags, the user can not only specify concrete tags but also a complete family by setting the ID
to “<family>”, so, e.g., “36h11”. All tags of this family will then be detected. It is further possible to
specify multiple complete tag families or a combination of concrete tags and complete tag families;
for instance, triggering for “36h11”, “25h9_3”, and “36h10” at the same time.
In addition to the ID, the approximate size (±10%) of a tag can be set with the size parameter.
As described in Pose estimation, Section 7.3.3, this information helps to resolve ambiguities in pose
estimation that may arise in certain situations.
Response: timestamp is set to the timestamp of the image pair the tag detection ran on.
tags contains all detected tags. id is the ID of the tag, similar to id in the request. instance
_
id
is the random unique identifier of the tag assigned by tag re-identification. pose contains position
and orientation. The orientation is in quaternion format. pose
_
frame is set to the coordinate frame
above pose refers to. It will always be “camera”. size will be set to the estimated tag size in meters;
for AprilTags, the white border is not included.
return
_
code holds possible warnings or error codes in value, which are represented by a value
greater than or less than 0, respectively. The respective error message can be found in message. The
7.3. TagDetect 82