voxel_grid_nodes

This is the design document for the voxel_grid_nodes package.

Purpose / Use cases

This package generally instantiates the objects and classes defined in the voxel_grid package for use with node constructs and general interprocess communication.

In short, this package exists to connect the voxel_grid family of objects to the larger ROS 2 infrastructure.

More concretely, the functionality in this package is needed because it allows us to downsample large point clouds into smaller point clouds, while still retaining a large amount of representational power.

Design

This package has 3 parts:

1. Base "algorithm" classes for interacting with an underlying voxel grid through the lens of the PointCloud2 messages
2. Instances of the base "algorithm" classes for different kinds of voxel grids, e.g. Approximate or Centroid
3. A node wrapper around the PointCloud2 algorithm class

The use of a base "algorithm" class is motivated by the fact that the underlying VoxelGrid class is templated, and has a template-dependent API (insofar as types are concerned). This means in order to get runtime dispatching/polymorphism (to keep the code base lighter and usage simpler), we must wrap the data structure in a polymorphic base class.

Assumptions / Known limits

The following limitations are present:

• The node allocates memory during runtime due to the following elements:
  • Underlying VoxelGrid data structure
  • Copying PointCloud2 header (due to a string frame_id)
  • General pub/sub allocates memory

Inputs / Outputs / API

The "algorithm" API is generally straightforward, with a single method for input and a single method for outputs. See the following API docs for more details:

• VoxelCloudBase

As a node, `VoxelCloudNode` has a standard set of public facing methods.

The inputs are a single PointCloud2 topic, and the outputs are another PointCloud2 topic.

Error detection and handling

Exceptions are generally thrown on errors.

The functionality in this package generally does not have error handling, as error handling is delegated to the underlying data structure.

Security considerations

TBD by a security specialist

References / External links

Future extensions / Unimplemented parts

• Memory allocation must be cleaned up
• Integration tests should be added

Related issues