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ar track alvar - how to detect custom IDs

asked 2014-02-11 01:32:53 -0600

psei gravatar image

Hello community!

I've got a question about tracking AR Tags with the "ar_track_alvar" package. I set up the package and subscrided to my kinect image topic. Everything runs fine. The tags, that come with the package (ID 0-20), are detected immediately and I see the corresponding TFs in rviz. So far, so good...

But now I wanted to create my own AR Tags, that carry additional information beyond a number called "ID" (e.g. the name/number of a room) to use them as landmarks. But as it turns out, the ar track alvar node seems to recognize just some of my custom AR tags. Tags that contain real text information like "Room G 301" aren't recognized at all, and even Tags that just contain a pure ID (e.g. "167") are not recognized. But in some cases (e.g. "200"), the ID is recognized.

I tried different sizes, distances, angles.... could not find a pattern. Does anyone know why the ar track alvar is so choosey in what it recognized and what not?

regards psei

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Hi, I'm a beginner in ROS that I need it for my project. Is there a tutorial that explains how to 1-connect camera to ROS in order to see the frames captured. 2-Identify the AR Tags I'm looking for some code examples. I only found one that deals with CUBE/SPHERE...etc. Nothing about codes that detects AR tags. Thank you

miloup gravatar image miloup  ( 2014-03-30 20:58:38 -0600 )edit

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answered 2014-02-15 10:09:13 -0600

sniekum gravatar image

I'm not sure how you are going about making your own AR tags, but the only supported way to make AR tags with ar_track_alvar is the included executable that produces them from given parameters. AR tags are not a single monolithic standard, so I'm assuming you are trying to use some protocol that you've seen with other types of AR tags to encode the information. ar_track_alvar only supports encoded ID numbers and those are produced through the included executable.

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Even with the ros node that creates the markers, most of them are not detectable. Say you add a string with the ar tag. It is not able to detect it

hc gravatar image hc  ( 2016-09-08 05:18:43 -0600 )edit

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Asked: 2014-02-11 01:32:53 -0600

Seen: 1,658 times

Last updated: Mar 30 '14