The Entity Path Hierarchy

Entity paths

As mentioned in the Entity Component overview, all entities within Rerun have a unique entity path.

The first argument to the log() function is this path. Each time you log to a specific entity path you will update the entity, i.e. log a new instance of it along the timeline.

It is possible to log multiple types of archetypes on the same entity path, but you should generally avoid mixing different kinds of geometric primitive. For example, logging a Points3D point cloud on an entity path where a Mesh3D was previously logged would overwrite the mesh's Position3D component with the point cloud's, but would leave the MeshProperties component untouched. The Rerun viewer would likely be unable to display the result. See the Entity Component section for more information.

There are valid reasons to logs different kinds of archetypes to the same entity path, though. For example, it's common to log a Transform3D along with some geometry it relates to (see the Spaces and Transforms for more info).

Rerun treats entity paths as being arranged in a hierarchy with the / character acting as a separator between path elements. The conventional path semantics including concepts of root and parent/child generally apply.

When writing paths in logging APIs the leading / is usually omitted.

In the file path analogy, each entity is a folder, and a component is a file. This implies that any entity in a hierarchy can contain components.

For example (this uses the Python SDK but the same applies for all supported languages):

rr.log("image", rr.Image(img)) rr.log("image/points", rr.Points2D(points))

It is also acceptable to leave implicitly "empty" entities in your paths as well.

rr.log("camera/image", rr.Image(img)) rr.log("camera/image/detections/points", rr.Points2D(points))

Nothing needs to be explicitly logged to "camera" or "camera/image/detection" to make the above valid. In other words, the log call is akin to creating a folder with mkdir -p and then writing files (components) to it. Existing components of the same name will be overwritten.

Path parts

Each "part" of a path must be a non-empty string. Any character is allowed, but special characters need to be escaped using \. Characters that need NOT be escaped are letters, numbers, and underscore, dash, and dot (_, -, .). Any other character should be escaped, including symbols (\:, \$, …) and whitespace (\ , \n, \t, …).

You can an arbitrary unicode code point into an entity path using \u{262E}.

So for instance, world/3D/My\ Image.jpg/detection is a valid path (note the escaped space!).

⚠️ NOTE: even though entity paths are somewhat analogous to file paths, they are NOT the same. .. does not mean "parent folder", and you are NOT intended to pass a file path as an entity path (especially not on Windows, which use \ as a path separator).

Path hierarchy functions

Path hierarchy plays an important role in a number of different functions within Rerun:

  • With the Transform System the transform component logged to any entity always describes the relationship between that entity and its direct parent.
  • When resolving the meaning of ClassId and KeypointId components, Rerun uses the Annotation Context from the nearest ancestor in the hierarchy.
  • When adding data to Blueprints, it is common to add a path and all of its descendants.
  • When using rr.log("entity/path", rr.Clear(recursive=True)), it marks an entity and all of its descendants as being cleared.
  • In the future, it will also be possible to use path-hierarchy to set default-values for descendants (#1158).

Reserved paths

The path prefix rerun/ is considered reserved for use by the Rerun SDK itself and should not be used for logging user data. This is where Rerun will log additional information such as warnings.