Annotate object links
With the object linking feature you can annotate relations or links between objects in the scene. These links can also contain link attributes.
The format of the link annotations in the exported label attributes is documented here.
Enable the object linking feature
Navigate to the dataset settings and go to the "Labeling" section. At the bottom of the page, check the option "Use object linking". If the option is not present, it means that the dataset is not compatible yet (see limitations above).
Enable category restrictions
With the "Enable category restrictions" flag disabled, links can be created between any two objects. With the flag enabled (default), links can only be created between whitelisted categories. These categories need to be configured in the categories editor.
Configure link attributes and category restrictions
Link attributes and category restrictions can be configured in the category editor.
Category restrictions
Configure which categories can be linked to the current category by adding them in the "Allow linking with these categories" input field. If a category can be linked to itself, it should also be added in the list. Since links have a direction, pay attention to which categories are added to each configuration.
Link attributes
Once the feature is activated, it's possible (but not required) to configure link attributes for each category.
Note that a link has a direction, from one object to another one. The attributes that will appear when annotating a link from one object to another one are determined by the from category.
Link attributes can also be configured programmatically.
Link two objects and edit link attributes
The tool bar has a new button to activate the object linking tool.
The below video shows how to link two objects, in this case a traffic light and a lane:
Select an object
Activate the object linking tool
Click on the other object you want to link it to
The link is now shown in the right sidebar. You can also set the link attributes here.
Unlink two objects
The following video shows how to delete a link:
Select the object
Select the object linking tool
Click on the other object to break the link
Alternatively a link can be deleted by clicking the trash bin icon in the sidebar next to the link.
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