
Limitations

The following limitations apply when using TagSLAM:

1. No duplicate tag ids are allowed! A tag can only exist in the world once. You must make sure that there are no duplicate tags anywhere.
• To use odometry with TagSLAM, the odometry updates should preferably be synchronized with the tag detections, for example the odometry should be computed from the same camera that does the camera recording. Starting release 2.1 TagSLAM accepts approximately synced data as well. This means that TagSLAM first filters the data approximately by running a filter identical to the ROS ApproximateTime synchronizer. The frequency of the slowest sensor will determine the frequency of TagSLAM pose updates, and higher-frequency data inbetween will be dropped. If you want to have higher frequency data, you need to insert for instance empty tag detection messages. Note that by default the use_approximate_sync feature is disabled, so if you feed in unsynchronized data all of it will be dropped.
• No mixing of AprilTag families! For a single data set, all tags must be of the same family
• All tags must have the same number of border bits.
• Real-time usage is limited to situations where either the graph is so small that it can be solved quickly (maybe a thousand frames maximum!), or the pose of the tags can be determined beforehand, offline, with a “mapping run” that builds the full graph, and then stores the optimized tag poses for a subsequent real-time run. To get real-time performance, use the “amnesia” feature such that old information gets thrown away and the graph stays small.

Note: restrictions 3. and 4. are due to the tag detector, and if fixed there, TagSLAM should be able to handle it.