Note: This is a rather advanced topic. Feel free to understand how it works prior to configuring your own transformer.

When data is processed by your robotic system, there will usually be quite a number of transformations between different frames, e.g. between a laser scanner and the body-center of the robot. Rock’s transformer handles the processing of geometrical information, so that in each component, only the needed transformations have to be specified, while transformations specified in other components are made available during runtime.

Inside the bundle, the transformer file is located in config/transforms.rb.

Static transformations are declared as follows:

static_transform translation, rotation,
"source_frame_name" => "target_frame_name"

Translation and rotations are resp. specified with Eigen::Vector3d and Eigen::Quaternion. The very useful Eigen::Quaternion.from_axis(angle, axis) call is often used in these files. The translation or rotation can be omitted if they are identities.

Dynamic transformations are declared as follows:

dynamic_transform "producer_task_name.port_name",
"source_frame_name" => "target_frame_name",

Where producer_task_name and port_name refer to the data stream that defines the required transformation. If the task has only one RigidBodyState output port, the port name can be left empty.

An example for a configuration file might look as follows:

# The frame names in this file are arbitrary !
static_transform Eigen::Vector3d.new(0.3, 0, 0),
"Body" => "ServoFrom"
static_transform Eigen::Quaternion.from_angle_axis
(1, Eigen::Vector3d::UnitX),
"ServoTo" => "Lidar",
dynamic_transform "servo.transform_samples",
"ServoFrom" => "ServoTo",

As you can see, the transforms.rb file contains the global information about which transformation is specified in which task. Look here for more information about how transformations are specified in oroGen components.